[PATCH 00/34] nd/multiple-work-trees reroll

[PATCH 00/34] nd/multiple-work-trees reroll

[Nguyễn Thái Ngọc Duy]

This is rebased so the diff below (against the version on Junio's
repo) is only approximate. Changes include test fixes for Windows
port, $GIT_COMMON_DIR and $GIT_DIR/modules problems with submodules.
Patch 03/34 is rewritten to touch less in refs.c to reduce conflicts.
A lot of changes there are just revert.

diff --git a/Documentation/gitrepository-layout.txt b/Documentation/gitrepository-layout.txt
index 2b30a92..7173b38 100644
--- a/Documentation/gitrepository-layout.txt
+++ b/Documentation/gitrepository-layout.txt
@@ -248,9 +248,7 @@ commondir::
 	incomplete without the repository pointed by "commondir".
 
 modules::
-	Contains the git-repositories of the submodules. This
-	directory is ignored if $GIT_COMMON_DIR is set and
-	"$GIT_COMMON_DIR/modules" will be used instead.
+	Contains the git-repositories of the submodules.
 
 worktrees::
 	Contains worktree specific information of linked
diff --git a/builtin/checkout.c b/builtin/checkout.c
index 01d0f2f..e70e66c 100644
--- a/builtin/checkout.c
+++ b/builtin/checkout.c
@@ -865,7 +865,7 @@ static int prepare_linked_checkout(const struct checkout_opts *opts,
 
 	if (!new->commit)
 		die(_("no branch specified"));
-	if (file_exists(path))
+	if (file_exists(path) && !is_empty_dir(path))
 		die(_("'%s' already exists"), path);
 
 	len = strlen(path);
@@ -1207,7 +1207,7 @@ static int parse_branchname_arg(int argc, const char **argv,
 	if (new->path && !force_detach && !*new_branch) {
 		unsigned char sha1[20];
 		int flag;
-		char *head_ref = resolve_refdup("HEAD", sha1, 0, &flag);
+		char *head_ref = resolve_refdup("HEAD", 0, sha1, &flag);
 		if (head_ref &&
 		    (!(flag & REF_ISSYMREF) || strcmp(head_ref, new->path)))
 			check_linked_checkouts(new);
diff --git a/environment.c b/environment.c
index d5b0788..8351007 100644
--- a/environment.c
+++ b/environment.c
@@ -101,6 +101,7 @@ const char * const local_repo_env[] = {
 	NO_REPLACE_OBJECTS_ENVIRONMENT,
 	GIT_PREFIX_ENVIRONMENT,
 	GIT_SHALLOW_FILE_ENVIRONMENT,
+	GIT_COMMON_DIR_ENVIRONMENT,
 	NULL
 };
 
diff --git a/path.c b/path.c
index 35d498e..a5c51a3 100644
--- a/path.c
+++ b/path.c
@@ -92,7 +92,7 @@ static void replace_dir(struct strbuf *buf, int len, const char *newdir)
 }
 
 static const char *common_list[] = {
-	"/branches", "/hooks", "/info", "!/logs", "/lost-found", "/modules",
+	"/branches", "/hooks", "/info", "!/logs", "/lost-found",
 	"/objects", "/refs", "/remotes", "/worktrees", "/rr-cache", "/svn",
 	"config", "!gc.pid", "packed-refs", "shallow",
 	NULL
diff --git a/refs.c b/refs.c
index 3cefbd3..f7e48b0 100644
--- a/refs.c
+++ b/refs.c
@@ -1398,14 +1398,16 @@ static const char *handle_missing_loose_ref(const char *refname,
 }
 
 /* This function needs to return a meaningful errno on failure */
-const char *resolve_ref_unsafe(const char *refname, unsigned char *sha1, int reading, int *flag)
+static const char *resolve_ref_unsafe_1(const char *refname,
+					unsigned char *sha1,
+					int reading,
+					int *flags,
+					struct strbuf *sb_path)
 {
-	struct strbuf sb_path = STRBUF_INIT;
 	int depth = MAXDEPTH;
 	ssize_t len;
 	char buffer[256];
 	static char refname_buffer[256];
-	const char *ret;
 
 	if (flag)
 		*flag = 0;
@@ -1423,12 +1425,12 @@ const char *resolve_ref_unsafe(const char *refname, unsigned char *sha1, int rea
 
 		if (--depth < 0) {
 			errno = ELOOP;
-			goto fail;
+			return NULL;
 		}
 
-		strbuf_reset(&sb_path);
-		strbuf_git_path(&sb_path, "%s", refname);
-		path = sb_path.buf;
+		strbuf_reset(sb_path);
+		strbuf_git_path(sb_path, "%s", refname);
+		path = sb_path->buf;
 
 		/*
 		 * We might have to loop back here to avoid a race
@@ -1442,11 +1444,10 @@ const char *resolve_ref_unsafe(const char *refname, unsigned char *sha1, int rea
 	stat_ref:
 		if (lstat(path, &st) < 0) {
 			if (errno == ENOENT)
-				ret = handle_missing_loose_ref(refname, sha1,
-							       reading, flag);
+				return handle_missing_loose_ref(refname, sha1,
+								reading, flag);
 			else
-				ret = NULL;
-			goto done;
+				return NULL;
 		}
 
 		/* Follow "normalized" - ie "refs/.." symlinks by hand */
@@ -1457,7 +1458,7 @@ const char *resolve_ref_unsafe(const char *refname, unsigned char *sha1, int rea
 					/* inconsistent with lstat; retry */
 					goto stat_ref;
 				else
-					goto fail;
+					return NULL;
 			}
 			buffer[len] = 0;
 			if (starts_with(buffer, "refs/") &&
@@ -1473,7 +1474,7 @@ const char *resolve_ref_unsafe(const char *refname, unsigned char *sha1, int rea
 		/* Is it a directory? */
 		if (S_ISDIR(st.st_mode)) {
 			errno = EISDIR;
-			goto fail;
+			return NULL;
 		}
 
 		/*
@@ -1486,15 +1487,14 @@ const char *resolve_ref_unsafe(const char *refname, unsigned char *sha1, int rea
 				/* inconsistent with lstat; retry */
 				goto stat_ref;
 			else
-				goto fail;
+				return NULL;
 		}
-
 		len = read_in_full(fd, buffer, sizeof(buffer)-1);
 		if (len < 0) {
 			int save_errno = errno;
 			close(fd);
 			errno = save_errno;
-			goto fail;
+			return NULL;
 		}
 		close(fd);
 		while (len && isspace(buffer[len-1]))
@@ -1514,10 +1514,9 @@ const char *resolve_ref_unsafe(const char *refname, unsigned char *sha1, int rea
 				if (flag)
 					*flag |= REF_ISBROKEN;
 				errno = EINVAL;
-				goto fail;
+				return NULL;
 			}
-			ret = refname;
-			goto done;
+			return refname;
 		}
 		if (flag)
 			*flag |= REF_ISSYMREF;
@@ -1528,13 +1527,17 @@ const char *resolve_ref_unsafe(const char *refname, unsigned char *sha1, int rea
 			if (flag)
 				*flag |= REF_ISBROKEN;
 			errno = EINVAL;
-			goto fail;
+			return NULL;
 		}
 		refname = strcpy(refname_buffer, buf);
 	}
-fail:
-	ret = NULL;
-done:
+}
+
+const char *resolve_ref_unsafe(const char *refname, int reading,
+			       unsigned char *sha1, int *flags)
+{
+	struct strbuf sb_path = STRBUF_INIT;
+	const char *ret = resolve_ref_unsafe_1(refname, reading,, sha1, flags, &sb_path);
 	strbuf_release(&sb_path);
 	return ret;
 }
@@ -2844,62 +2847,66 @@ static int copy_msg(char *buf, const char *msg)
 }
 
 /* This function must set a meaningful errno on failure */
-int log_ref_setup(const char *refname, struct strbuf *logfile)
+int log_ref_setup(const char *refname, struct strbuf *sb_logfile)
 {
 	int logfd, oflags = O_APPEND | O_WRONLY;
+	char *logfile;
 
-	strbuf_git_path(logfile, "logs/%s", refname);
+	strbuf_git_path(sb_logfile, "logs/%s", refname);
+	logfile = sb_logfile->buf;
+	/* make sure the rest of the function can't change "logfile" */
+	sb_logfile = NULL;
 	if (log_all_ref_updates &&
 	    (starts_with(refname, "refs/heads/") ||
 	     starts_with(refname, "refs/remotes/") ||
 	     starts_with(refname, "refs/notes/") ||
 	     !strcmp(refname, "HEAD"))) {
-		if (safe_create_leading_directories(logfile->buf) < 0) {
+		if (safe_create_leading_directories(logfile) < 0) {
 			int save_errno = errno;
-			error("unable to create directory for %s", logfile->buf);
+			error("unable to create directory for %s", logfile);
 			errno = save_errno;
 			return -1;
 		}
 		oflags |= O_CREAT;
 	}
 
-	logfd = open(logfile->buf, oflags, 0666);
+	logfd = open(logfile, oflags, 0666);
 	if (logfd < 0) {
 		if (!(oflags & O_CREAT) && errno == ENOENT)
 			return 0;
 
 		if ((oflags & O_CREAT) && errno == EISDIR) {
-			if (remove_empty_directories(logfile->buf)) {
+			if (remove_empty_directories(logfile)) {
 				int save_errno = errno;
 				error("There are still logs under '%s'",
-				      logfile->buf);
+				      logfile);
 				errno = save_errno;
 				return -1;
 			}
-			logfd = open(logfile->buf, oflags, 0666);
+			logfd = open(logfile, oflags, 0666);
 		}
 
 		if (logfd < 0) {
 			int save_errno = errno;
-			error("Unable to append to %s: %s", logfile->buf,
+			error("Unable to append to %s: %s", logfile,
 			      strerror(errno));
 			errno = save_errno;
 			return -1;
 		}
 	}
 
-	adjust_shared_perm(logfile->buf);
+	adjust_shared_perm(logfile);
 	close(logfd);
 	return 0;
 }
 
-static int log_ref_write(const char *refname, const unsigned char *old_sha1,
-			 const unsigned char *new_sha1, const char *msg)
+static int log_ref_write_1(const char *refname, const unsigned char *old_sha1,
+			   const unsigned char *new_sha1, const char *msg,
+			   struct strbuf *sb_log_file)
 {
 	int logfd, result, written, oflags = O_APPEND | O_WRONLY;
 	unsigned maxlen, len;
 	int msglen;
-	struct strbuf sb_log_file = STRBUF_INIT;
 	const char *log_file;
 	char *logrec;
 	const char *committer;
@@ -2907,14 +2914,16 @@ static int log_ref_write(const char *refname, const unsigned char *old_sha1,
 	if (log_all_ref_updates < 0)
 		log_all_ref_updates = !is_bare_repository();
 
-	result = log_ref_setup(refname, &sb_log_file);
+	result = log_ref_setup(refname, sb_log_file);
 	if (result)
-		goto done;
-	log_file = sb_log_file.buf;
+		return result;
+	log_file = sb_log_file->buf;
+	/* make sure the rest of the function can't change "log_file" */
+	sb_log_file = NULL;
 
 	logfd = open(log_file, oflags);
 	if (logfd < 0)
-		goto done;
+		return 0;
 	msglen = msg ? strlen(msg) : 0;
 	committer = git_committer_info(0);
 	maxlen = strlen(committer) + msglen + 100;
@@ -2932,19 +2941,24 @@ static int log_ref_write(const char *refname, const unsigned char *old_sha1,
 		close(logfd);
 		error("Unable to append to %s", log_file);
 		errno = save_errno;
-		result = -1;
-		goto done;
+		return -1;
 	}
 	if (close(logfd)) {
 		int save_errno = errno;
 		error("Unable to append to %s", log_file);
 		errno = save_errno;
-		result = -1;
-		goto done;
+		return -1;
 	}
-done:
-	strbuf_release(&sb_log_file);
-	return result;
+	return 0;
+}
+
+static int log_ref_write(const char *refname, const unsigned char *old_sha1,
+			 const unsigned char *new_sha1, const char *msg)
+{
+	struct strbuf sb = STRBUF_INIT;
+	int ret = log_ref_write_1(refname, old_sha1, new_sha1, msg, &sb);
+	strbuf_release(&sb);
+	return ret;
 }
 
 int is_branch(const char *refname)
diff --git a/t/t1501-worktree.sh b/t/t1501-worktree.sh
index e6ac7a4..4df7a2f 100755
--- a/t/t1501-worktree.sh
+++ b/t/t1501-worktree.sh
@@ -366,7 +366,7 @@ test_expect_success 'GIT_DIR set (1)' '
 
 test_expect_success 'GIT_DIR set (2)' '
 	echo "gitdir: repo.git/repos/foo" >gitfile &&
-	echo "$TRASH_DIRECTORY/repo.git" >repo.git/repos/foo/commondir &&
+	echo "$(pwd)/repo.git" >repo.git/repos/foo/commondir &&
 	(
 		cd work &&
 		GIT_DIR=../gitfile git rev-parse --git-common-dir >actual &&
diff --git a/t/t2025-checkout-to.sh b/t/t2025-checkout-to.sh
index eddd325..915b506 100755
--- a/t/t2025-checkout-to.sh
+++ b/t/t2025-checkout-to.sh
@@ -13,10 +13,15 @@ test_expect_success 'checkout --to not updating paths' '
 '
 
 test_expect_success 'checkout --to an existing worktree' '
-	mkdir existing &&
+	mkdir -p existing/subtree &&
 	test_must_fail git checkout --detach --to existing master
 '
 
+test_expect_success 'checkout --to an existing empty worktree' '
+	mkdir existing_empty &&
+	git checkout --detach --to existing_empty master
+'
+
 test_expect_success 'checkout --to refuses to checkout locked branch' '
 	test_must_fail git checkout --to zere master &&
 	! test -d zere &&
diff --git a/t/t2026-prune-linked-checkouts.sh b/t/t2026-prune-linked-checkouts.sh
index 3622800..170aefe 100755
--- a/t/t2026-prune-linked-checkouts.sh
+++ b/t/t2026-prune-linked-checkouts.sh
@@ -57,7 +57,7 @@ test_expect_success 'prune directories with invalid gitdir' '
 test_expect_success 'prune directories with gitdir pointing to nowhere' '
 	mkdir -p .git/worktrees/def/abc &&
 	: >.git/worktrees/def/def &&
-	echo "$TRASH_DIRECTORY"/nowhere >.git/worktrees/def/gitdir &&
+	echo "$(pwd)"/nowhere >.git/worktrees/def/gitdir &&
 	git prune --worktrees --verbose >actual &&
 	test_i18ngrep "Removing worktrees/def: gitdir file points to non-existent location" actual &&
 	! test -d .git/worktrees/def &&
@@ -76,7 +76,7 @@ test_expect_success 'not prune recent checkouts' '
 	test_when_finished rm -r .git/worktrees
 	mkdir zz &&
 	mkdir -p .git/worktrees/jlm &&
-	echo "$TRASH_DIRECTORY"/zz >.git/worktrees/jlm/gitdir &&
+	echo "$(pwd)"/zz >.git/worktrees/jlm/gitdir &&
 	git prune --worktrees --verbose --expire=2.days.ago &&
 	test -d .git/worktrees/jlm
 '
diff --git a/t/t7410-submodule-checkout-to.sh b/t/t7410-submodule-checkout-to.sh
new file mode 100755
index 0000000..8f30aed
--- /dev/null
+++ b/t/t7410-submodule-checkout-to.sh
@@ -0,0 +1,50 @@
+#!/bin/sh
+
+test_description='Combination of submodules and multiple workdirs'
+
+. ./test-lib.sh
+
+base_path=$(pwd -P)
+
+test_expect_success 'setup: make origin' \
+    'mkdir -p origin/sub && ( cd origin/sub && git init &&
+	echo file1 >file1 &&
+	git add file1 &&
+	git commit -m file1 ) &&
+    mkdir -p origin/main && ( cd origin/main && git init &&
+	git submodule add ../sub &&
+	git commit -m "add sub" ) &&
+    ( cd origin/sub &&
+	echo file1updated >file1 &&
+	git add file1 &&
+	git commit -m "file1 updated" ) &&
+    ( cd origin/main/sub && git pull ) &&
+    ( cd origin/main &&
+	git add sub &&
+	git commit -m "sub updated" )'
+
+test_expect_success 'setup: clone' \
+    'mkdir clone && ( cd clone &&
+	git clone --recursive "$base_path/origin/main")'
+
+rev1_hash_main=$(git --git-dir=origin/main/.git show --pretty=format:%h -q "HEAD~1")
+rev1_hash_sub=$(git --git-dir=origin/sub/.git show --pretty=format:%h -q "HEAD~1")
+
+test_expect_success 'checkout main' \
+    'mkdir default_checkout &&
+    (cd clone/main &&
+	git checkout --to "$base_path/default_checkout/main" "$rev1_hash_main")'
+
+test_expect_failure 'can see submodule diffs just after checkout' \
+    '(cd default_checkout/main && git diff --submodule master"^!" | grep "file1 updated")'
+
+test_expect_success 'checkout main and initialize independed clones' \
+    'mkdir fully_cloned_submodule &&
+    (cd clone/main &&
+	git checkout --to "$base_path/fully_cloned_submodule/main" "$rev1_hash_main") &&
+    (cd fully_cloned_submodule/main && git submodule update)'
+
+test_expect_success 'can see submodule diffs after independed cloning' \
+    '(cd fully_cloned_submodule/main && git diff --submodule master"^!" | grep "file1 updated")'
+
+test_done

[PATCH 01/34] path.c: make get_pathname() return strbuf instead of static buffer

[Nguyễn Thái Ngọc Duy]

We've been avoiding PATH_MAX whenever possible. This patch makes
get_pathname() return a strbuf and updates the callers to take
advantage of this. The code is simplified as we no longer need to
worry about buffer overflow.

vsnpath() behavior is changed slightly: previously it always clears
the buffer before writing, now it just appends. Fortunately this is a
static function and all of its callers prepare the buffer properly:
git_path() gets the buffer from get_pathname() which resets the
buffer, the remaining call sites start with STRBUF_INIT'd buffer.

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
---
 path.c | 120 ++++++++++++++++++++++++++++-------------------------------------
 1 file changed, 51 insertions(+), 69 deletions(-)

diff --git a/path.c b/path.c
index f68df0c..015c0e4 100644
--- a/path.c
+++ b/path.c
@@ -16,11 +16,15 @@ static int get_st_mode_bits(const char *path, int *mode)
 
 static char bad_path[] = "/bad-path/";
 
-static char *get_pathname(void)
+static struct strbuf *get_pathname(void)
 {
-	static char pathname_array[4][PATH_MAX];
+	static struct strbuf pathname_array[4] = {
+		STRBUF_INIT, STRBUF_INIT, STRBUF_INIT, STRBUF_INIT
+	};
 	static int index;
-	return pathname_array[3 & ++index];
+	struct strbuf *sb = &pathname_array[3 & ++index];
+	strbuf_reset(sb);
+	return sb;
 }
 
 static char *cleanup_path(char *path)
@@ -34,6 +38,13 @@ static char *cleanup_path(char *path)
 	return path;
 }
 
+static void strbuf_cleanup_path(struct strbuf *sb)
+{
+	char *path = cleanup_path(sb->buf);
+	if (path > sb->buf)
+		strbuf_remove(sb, 0, path - sb->buf);
+}
+
 char *mksnpath(char *buf, size_t n, const char *fmt, ...)
 {
 	va_list args;
@@ -49,85 +60,70 @@ char *mksnpath(char *buf, size_t n, const char *fmt, ...)
 	return cleanup_path(buf);
 }
 
-static char *vsnpath(char *buf, size_t n, const char *fmt, va_list args)
+static void vsnpath(struct strbuf *buf, const char *fmt, va_list args)
 {
 	const char *git_dir = get_git_dir();
-	size_t len;
-
-	len = strlen(git_dir);
-	if (n < len + 1)
-		goto bad;
-	memcpy(buf, git_dir, len);
-	if (len && !is_dir_sep(git_dir[len-1]))
-		buf[len++] = '/';
-	len += vsnprintf(buf + len, n - len, fmt, args);
-	if (len >= n)
-		goto bad;
-	return cleanup_path(buf);
-bad:
-	strlcpy(buf, bad_path, n);
-	return buf;
+	strbuf_addstr(buf, git_dir);
+	if (buf->len && !is_dir_sep(buf->buf[buf->len - 1]))
+		strbuf_addch(buf, '/');
+	strbuf_vaddf(buf, fmt, args);
+	strbuf_cleanup_path(buf);
 }
 
 char *git_snpath(char *buf, size_t n, const char *fmt, ...)
 {
-	char *ret;
+	struct strbuf sb = STRBUF_INIT;
 	va_list args;
 	va_start(args, fmt);
-	ret = vsnpath(buf, n, fmt, args);
+	vsnpath(&sb, fmt, args);
 	va_end(args);
-	return ret;
+	if (sb.len >= n)
+		strlcpy(buf, bad_path, n);
+	else
+		memcpy(buf, sb.buf, sb.len + 1);
+	strbuf_release(&sb);
+	return buf;
 }
 
 char *git_pathdup(const char *fmt, ...)
 {
-	char path[PATH_MAX], *ret;
+	struct strbuf path = STRBUF_INIT;
 	va_list args;
 	va_start(args, fmt);
-	ret = vsnpath(path, sizeof(path), fmt, args);
+	vsnpath(&path, fmt, args);
 	va_end(args);
-	return xstrdup(ret);
+	return strbuf_detach(&path, NULL);
 }
 
 char *mkpathdup(const char *fmt, ...)
 {
-	char *path;
 	struct strbuf sb = STRBUF_INIT;
 	va_list args;
-
 	va_start(args, fmt);
 	strbuf_vaddf(&sb, fmt, args);
 	va_end(args);
-	path = xstrdup(cleanup_path(sb.buf));
-
-	strbuf_release(&sb);
-	return path;
+	strbuf_cleanup_path(&sb);
+	return strbuf_detach(&sb, NULL);
 }
 
 char *mkpath(const char *fmt, ...)
 {
 	va_list args;
-	unsigned len;
-	char *pathname = get_pathname();
-
+	struct strbuf *pathname = get_pathname();
 	va_start(args, fmt);
-	len = vsnprintf(pathname, PATH_MAX, fmt, args);
+	strbuf_vaddf(pathname, fmt, args);
 	va_end(args);
-	if (len >= PATH_MAX)
-		return bad_path;
-	return cleanup_path(pathname);
+	return cleanup_path(pathname->buf);
 }
 
 char *git_path(const char *fmt, ...)
 {
-	char *pathname = get_pathname();
+	struct strbuf *pathname = get_pathname();
 	va_list args;
-	char *ret;
-
 	va_start(args, fmt);
-	ret = vsnpath(pathname, PATH_MAX, fmt, args);
+	vsnpath(pathname, fmt, args);
 	va_end(args);
-	return ret;
+	return pathname->buf;
 }
 
 void home_config_paths(char **global, char **xdg, char *file)
@@ -160,41 +156,27 @@ void home_config_paths(char **global, char **xdg, char *file)
 
 char *git_path_submodule(const char *path, const char *fmt, ...)
 {
-	char *pathname = get_pathname();
-	struct strbuf buf = STRBUF_INIT;
+	struct strbuf *buf = get_pathname();
 	const char *git_dir;
 	va_list args;
-	unsigned len;
-
-	len = strlen(path);
-	if (len > PATH_MAX-100)
-		return bad_path;
 
-	strbuf_addstr(&buf, path);
-	if (len && path[len-1] != '/')
-		strbuf_addch(&buf, '/');
-	strbuf_addstr(&buf, ".git");
+	strbuf_addstr(buf, path);
+	if (buf->len && buf->buf[buf->len - 1] != '/')
+		strbuf_addch(buf, '/');
+	strbuf_addstr(buf, ".git");
 
-	git_dir = read_gitfile(buf.buf);
+	git_dir = read_gitfile(buf->buf);
 	if (git_dir) {
-		strbuf_reset(&buf);
-		strbuf_addstr(&buf, git_dir);
+		strbuf_reset(buf);
+		strbuf_addstr(buf, git_dir);
 	}
-	strbuf_addch(&buf, '/');
-
-	if (buf.len >= PATH_MAX)
-		return bad_path;
-	memcpy(pathname, buf.buf, buf.len + 1);
-
-	strbuf_release(&buf);
-	len = strlen(pathname);
+	strbuf_addch(buf, '/');
 
 	va_start(args, fmt);
-	len += vsnprintf(pathname + len, PATH_MAX - len, fmt, args);
+	strbuf_vaddf(buf, fmt, args);
 	va_end(args);
-	if (len >= PATH_MAX)
-		return bad_path;
-	return cleanup_path(pathname);
+	strbuf_cleanup_path(buf);
+	return buf->buf;
 }
 
 int validate_headref(const char *path)
-- 
2.1.0.rc0.78.gc0d8480

[PATCH 02/34] path.c: make get_pathname() call sites return const char *

[Nguyễn Thái Ngọc Duy]

Before the previous commit, get_pathname returns an array of PATH_MAX
length. Even if git_path() and similar functions does not use the
whole array, git_path() caller can, in theory.

After the commit, get_pathname() may return a buffer that has just
enough room for the returned string and git_path() caller should never
write beyond that.

Make git_path(), mkpath() and git_path_submodule() return a const
buffer to make sure callers do not write in it at all.

This could have been part of the previous commit, but the "const"
conversion is too much distraction from the core changes in path.c.

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
---
 builtin/checkout.c     | 2 +-
 builtin/clone.c        | 9 +++++----
 builtin/fetch.c        | 5 +++--
 builtin/fsck.c         | 4 ++--
 builtin/receive-pack.c | 2 +-
 builtin/remote.c       | 2 +-
 builtin/repack.c       | 8 +++++---
 cache.h                | 6 +++---
 fast-import.c          | 2 +-
 notes-merge.c          | 6 +++---
 path.c                 | 6 +++---
 refs.c                 | 8 ++++----
 run-command.c          | 4 ++--
 run-command.h          | 2 +-
 sha1_file.c            | 2 +-
 15 files changed, 36 insertions(+), 32 deletions(-)

diff --git a/builtin/checkout.c b/builtin/checkout.c
index 5410dac..c600ec1 100644
--- a/builtin/checkout.c
+++ b/builtin/checkout.c
@@ -589,7 +589,7 @@ static void update_refs_for_switch(const struct checkout_opts *opts,
 			if (opts->new_branch_log && !log_all_ref_updates) {
 				int temp;
 				char log_file[PATH_MAX];
-				char *ref_name = mkpath("refs/heads/%s", opts->new_orphan_branch);
+				const char *ref_name = mkpath("refs/heads/%s", opts->new_orphan_branch);
 
 				temp = log_all_ref_updates;
 				log_all_ref_updates = 1;
diff --git a/builtin/clone.c b/builtin/clone.c
index d5e7532..a9af3f2 100644
--- a/builtin/clone.c
+++ b/builtin/clone.c
@@ -290,16 +290,17 @@ static void copy_alternates(struct strbuf *src, struct strbuf *dst,
 	struct strbuf line = STRBUF_INIT;
 
 	while (strbuf_getline(&line, in, '\n') != EOF) {
-		char *abs_path, abs_buf[PATH_MAX];
+		char *abs_path;
 		if (!line.len || line.buf[0] == '#')
 			continue;
 		if (is_absolute_path(line.buf)) {
 			add_to_alternates_file(line.buf);
 			continue;
 		}
-		abs_path = mkpath("%s/objects/%s", src_repo, line.buf);
-		normalize_path_copy(abs_buf, abs_path);
-		add_to_alternates_file(abs_buf);
+		abs_path = mkpathdup("%s/objects/%s", src_repo, line.buf);
+		normalize_path_copy(abs_path, abs_path);
+		add_to_alternates_file(abs_path);
+		free(abs_path);
 	}
 	strbuf_release(&line);
 	fclose(in);
diff --git a/builtin/fetch.c b/builtin/fetch.c
index 7b84d35..cb54936 100644
--- a/builtin/fetch.c
+++ b/builtin/fetch.c
@@ -587,7 +587,8 @@ static int store_updated_refs(const char *raw_url, const char *remote_name,
 	struct strbuf note = STRBUF_INIT;
 	const char *what, *kind;
 	struct ref *rm;
-	char *url, *filename = dry_run ? "/dev/null" : git_path("FETCH_HEAD");
+	char *url;
+	const char *filename = dry_run ? "/dev/null" : git_path("FETCH_HEAD");
 	int want_status;
 
 	fp = fopen(filename, "a");
@@ -821,7 +822,7 @@ static void check_not_current_branch(struct ref *ref_map)
 
 static int truncate_fetch_head(void)
 {
-	char *filename = git_path("FETCH_HEAD");
+	const char *filename = git_path("FETCH_HEAD");
 	FILE *fp = fopen(filename, "w");
 
 	if (!fp)
diff --git a/builtin/fsck.c b/builtin/fsck.c
index a27515a..b92aeff 100644
--- a/builtin/fsck.c
+++ b/builtin/fsck.c
@@ -225,12 +225,12 @@ static void check_unreachable_object(struct object *obj)
 			printf("dangling %s %s\n", typename(obj->type),
 			       sha1_to_hex(obj->sha1));
 		if (write_lost_and_found) {
-			char *filename = git_path("lost-found/%s/%s",
+			const char *filename = git_path("lost-found/%s/%s",
 				obj->type == OBJ_COMMIT ? "commit" : "other",
 				sha1_to_hex(obj->sha1));
 			FILE *f;
 
-			if (safe_create_leading_directories(filename)) {
+			if (safe_create_leading_directories_const(filename)) {
 				error("Could not create lost-found");
 				return;
 			}
diff --git a/builtin/receive-pack.c b/builtin/receive-pack.c
index 32fc540..3b8f420 100644
--- a/builtin/receive-pack.c
+++ b/builtin/receive-pack.c
@@ -869,7 +869,7 @@ static void run_update_post_hook(struct command *commands)
 	int argc;
 	const char **argv;
 	struct child_process proc = CHILD_PROCESS_INIT;
-	char *hook;
+	const char *hook;
 
 	hook = find_hook("post-update");
 	for (argc = 0, cmd = commands; cmd; cmd = cmd->next) {
diff --git a/builtin/remote.c b/builtin/remote.c
index 7f28f92..4ce396f 100644
--- a/builtin/remote.c
+++ b/builtin/remote.c
@@ -582,7 +582,7 @@ static int migrate_file(struct remote *remote)
 {
 	struct strbuf buf = STRBUF_INIT;
 	int i;
-	char *path = NULL;
+	const char *path = NULL;
 
 	strbuf_addf(&buf, "remote.%s.url", remote->name);
 	for (i = 0; i < remote->url_nr; i++)
diff --git a/builtin/repack.c b/builtin/repack.c
index 2845620..9c04e1d 100644
--- a/builtin/repack.c
+++ b/builtin/repack.c
@@ -284,7 +284,8 @@ int cmd_repack(int argc, const char **argv, const char *prefix)
 	failed = 0;
 	for_each_string_list_item(item, &names) {
 		for (ext = 0; ext < ARRAY_SIZE(exts); ext++) {
-			char *fname, *fname_old;
+			const char *fname_old;
+			char *fname;
 			fname = mkpathdup("%s/pack-%s%s", packdir,
 						item->string, exts[ext].name);
 			if (!file_exists(fname)) {
@@ -312,7 +313,8 @@ int cmd_repack(int argc, const char **argv, const char *prefix)
 	if (failed) {
 		struct string_list rollback_failure = STRING_LIST_INIT_DUP;
 		for_each_string_list_item(item, &rollback) {
-			char *fname, *fname_old;
+			const char *fname_old;
+			char *fname;
 			fname = mkpathdup("%s/%s", packdir, item->string);
 			fname_old = mkpath("%s/old-%s", packdir, item->string);
 			if (rename(fname_old, fname))
@@ -365,7 +367,7 @@ int cmd_repack(int argc, const char **argv, const char *prefix)
 	/* Remove the "old-" files */
 	for_each_string_list_item(item, &names) {
 		for (ext = 0; ext < ARRAY_SIZE(exts); ext++) {
-			char *fname;
+			const char *fname;
 			fname = mkpath("%s/old-%s%s",
 					packdir,
 					item->string,
diff --git a/cache.h b/cache.h
index 99ed096..dbee0a3 100644
--- a/cache.h
+++ b/cache.h
@@ -687,9 +687,9 @@ extern char *mkpathdup(const char *fmt, ...)
 	__attribute__((format (printf, 1, 2)));
 
 /* Return a statically allocated filename matching the sha1 signature */
-extern char *mkpath(const char *fmt, ...) __attribute__((format (printf, 1, 2)));
-extern char *git_path(const char *fmt, ...) __attribute__((format (printf, 1, 2)));
-extern char *git_path_submodule(const char *path, const char *fmt, ...)
+extern const char *mkpath(const char *fmt, ...) __attribute__((format (printf, 1, 2)));
+extern const char *git_path(const char *fmt, ...) __attribute__((format (printf, 1, 2)));
+extern const char *git_path_submodule(const char *path, const char *fmt, ...)
 	__attribute__((format (printf, 2, 3)));
 
 /*
diff --git a/fast-import.c b/fast-import.c
index d0bd285..3018130 100644
--- a/fast-import.c
+++ b/fast-import.c
@@ -405,7 +405,7 @@ static void dump_marks_helper(FILE *, uintmax_t, struct mark_set *);
 
 static void write_crash_report(const char *err)
 {
-	char *loc = git_path("fast_import_crash_%"PRIuMAX, (uintmax_t) getpid());
+	const char *loc = git_path("fast_import_crash_%"PRIuMAX, (uintmax_t) getpid());
 	FILE *rpt = fopen(loc, "w");
 	struct branch *b;
 	unsigned long lu;
diff --git a/notes-merge.c b/notes-merge.c
index 7eb9d7a..f39e906 100644
--- a/notes-merge.c
+++ b/notes-merge.c
@@ -280,7 +280,7 @@ static void check_notes_merge_worktree(struct notes_merge_options *o)
 				    "(%s exists).", git_path("NOTES_MERGE_*"));
 		}
 
-		if (safe_create_leading_directories(git_path(
+		if (safe_create_leading_directories_const(git_path(
 				NOTES_MERGE_WORKTREE "/.test")))
 			die_errno("unable to create directory %s",
 				  git_path(NOTES_MERGE_WORKTREE));
@@ -295,8 +295,8 @@ static void write_buf_to_worktree(const unsigned char *obj,
 				  const char *buf, unsigned long size)
 {
 	int fd;
-	char *path = git_path(NOTES_MERGE_WORKTREE "/%s", sha1_to_hex(obj));
-	if (safe_create_leading_directories(path))
+	const char *path = git_path(NOTES_MERGE_WORKTREE "/%s", sha1_to_hex(obj));
+	if (safe_create_leading_directories_const(path))
 		die_errno("unable to create directory for '%s'", path);
 	if (file_exists(path))
 		die("found existing file at '%s'", path);
diff --git a/path.c b/path.c
index 015c0e4..a7ceea2 100644
--- a/path.c
+++ b/path.c
@@ -106,7 +106,7 @@ char *mkpathdup(const char *fmt, ...)
 	return strbuf_detach(&sb, NULL);
 }
 
-char *mkpath(const char *fmt, ...)
+const char *mkpath(const char *fmt, ...)
 {
 	va_list args;
 	struct strbuf *pathname = get_pathname();
@@ -116,7 +116,7 @@ char *mkpath(const char *fmt, ...)
 	return cleanup_path(pathname->buf);
 }
 
-char *git_path(const char *fmt, ...)
+const char *git_path(const char *fmt, ...)
 {
 	struct strbuf *pathname = get_pathname();
 	va_list args;
@@ -154,7 +154,7 @@ void home_config_paths(char **global, char **xdg, char *file)
 	free(to_free);
 }
 
-char *git_path_submodule(const char *path, const char *fmt, ...)
+const char *git_path_submodule(const char *path, const char *fmt, ...)
 {
 	struct strbuf *buf = get_pathname();
 	const char *git_dir;
diff --git a/refs.c b/refs.c
index 5ff457e..23617e0 100644
--- a/refs.c
+++ b/refs.c
@@ -1351,7 +1351,7 @@ static int resolve_gitlink_ref_recursive(struct ref_cache *refs,
 {
 	int fd, len;
 	char buffer[128], *p;
-	char *path;
+	const char *path;
 
 	if (recursion > MAXDEPTH || strlen(refname) > MAXREFLEN)
 		return -1;
@@ -2229,7 +2229,7 @@ static struct ref_lock *lock_ref_sha1_basic(const char *refname,
 					    const struct string_list *skip,
 					    int flags, int *type_p)
 {
-	char *ref_file;
+	const char *ref_file;
 	const char *orig_refname = refname;
 	struct ref_lock *lock;
 	int last_errno = 0;
@@ -2303,7 +2303,7 @@ static struct ref_lock *lock_ref_sha1_basic(const char *refname,
 		lock->force_write = 1;
 
  retry:
-	switch (safe_create_leading_directories(ref_file)) {
+	switch (safe_create_leading_directories_const(ref_file)) {
 	case SCLD_OK:
 		break; /* success */
 	case SCLD_VANISHED:
@@ -2743,7 +2743,7 @@ static int rename_tmp_log(const char *newrefname)
 	int attempts_remaining = 4;
 
  retry:
-	switch (safe_create_leading_directories(git_path("logs/%s", newrefname))) {
+	switch (safe_create_leading_directories_const(git_path("logs/%s", newrefname))) {
 	case SCLD_OK:
 		break; /* success */
 	case SCLD_VANISHED:
diff --git a/run-command.c b/run-command.c
index a476999..c4a62aa 100644
--- a/run-command.c
+++ b/run-command.c
@@ -794,9 +794,9 @@ int finish_async(struct async *async)
 #endif
 }
 
-char *find_hook(const char *name)
+const char *find_hook(const char *name)
 {
-	char *path = git_path("hooks/%s", name);
+	const char *path = git_path("hooks/%s", name);
 	if (access(path, X_OK) < 0)
 		path = NULL;
 
diff --git a/run-command.h b/run-command.h
index 2137315..892892d 100644
--- a/run-command.h
+++ b/run-command.h
@@ -52,7 +52,7 @@ int start_command(struct child_process *);
 int finish_command(struct child_process *);
 int run_command(struct child_process *);
 
-extern char *find_hook(const char *name);
+extern const char *find_hook(const char *name);
 LAST_ARG_MUST_BE_NULL
 extern int run_hook_le(const char *const *env, const char *name, ...);
 extern int run_hook_ve(const char *const *env, const char *name, va_list args);
diff --git a/sha1_file.c b/sha1_file.c
index d7f1838..1ed74f9 100644
--- a/sha1_file.c
+++ b/sha1_file.c
@@ -405,7 +405,7 @@ void add_to_alternates_file(const char *reference)
 {
 	struct lock_file *lock = xcalloc(1, sizeof(struct lock_file));
 	int fd = hold_lock_file_for_append(lock, git_path("objects/info/alternates"), LOCK_DIE_ON_ERROR);
-	char *alt = mkpath("%s\n", reference);
+	const char *alt = mkpath("%s\n", reference);
 	write_or_die(fd, alt, strlen(alt));
 	if (commit_lock_file(lock))
 		die("could not close alternates file");
-- 
2.1.0.rc0.78.gc0d8480

[PATCH 03/34] git_snpath(): retire and replace with strbuf_git_path()

[Nguyễn Thái Ngọc Duy]

In the previous patch, git_snpath() is modified to allocate a new
strbuf buffer because vsnpath() needs that. But that makes it
awkward because git_snpath() receives a pre-allocated buffer from
outside and has to copy data back. Rename it to strbuf_git_path()
and make it receive strbuf directly.

Using git_path() in update_refs_for_switch() which used to call
git_snpath() is safe because that function and all of its callers do
not keep any pointer to the round-robin buffer pool allocated by
get_pathname().

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
---
 builtin/checkout.c | 13 ++++++++-----
 cache.h            |  4 ++--
 path.c             | 11 ++---------
 refs.c             | 51 ++++++++++++++++++++++++++++++++++++++++++---------
 refs.h             |  2 +-
 5 files changed, 55 insertions(+), 26 deletions(-)

diff --git a/builtin/checkout.c b/builtin/checkout.c
index c600ec1..195aca7 100644
--- a/builtin/checkout.c
+++ b/builtin/checkout.c
@@ -588,18 +588,21 @@ static void update_refs_for_switch(const struct checkout_opts *opts,
 		if (opts->new_orphan_branch) {
 			if (opts->new_branch_log && !log_all_ref_updates) {
 				int temp;
-				char log_file[PATH_MAX];
-				const char *ref_name = mkpath("refs/heads/%s", opts->new_orphan_branch);
+				struct strbuf log_file = STRBUF_INIT;
+				int ret;
+				const char *ref_name;
 
+				ref_name = mkpath("refs/heads/%s", opts->new_orphan_branch);
 				temp = log_all_ref_updates;
 				log_all_ref_updates = 1;
-				if (log_ref_setup(ref_name, log_file, sizeof(log_file))) {
+				ret = log_ref_setup(ref_name, &log_file);
+				log_all_ref_updates = temp;
+				strbuf_release(&log_file);
+				if (ret) {
 					fprintf(stderr, _("Can not do reflog for '%s'\n"),
 					    opts->new_orphan_branch);
-					log_all_ref_updates = temp;
 					return;
 				}
-				log_all_ref_updates = temp;
 			}
 		}
 		else
diff --git a/cache.h b/cache.h
index dbee0a3..56643cf 100644
--- a/cache.h
+++ b/cache.h
@@ -679,8 +679,8 @@ extern int check_repository_format(void);
 
 extern char *mksnpath(char *buf, size_t n, const char *fmt, ...)
 	__attribute__((format (printf, 3, 4)));
-extern char *git_snpath(char *buf, size_t n, const char *fmt, ...)
-	__attribute__((format (printf, 3, 4)));
+extern void strbuf_git_path(struct strbuf *sb, const char *fmt, ...)
+	__attribute__((format (printf, 2, 3)));
 extern char *git_pathdup(const char *fmt, ...)
 	__attribute__((format (printf, 1, 2)));
 extern char *mkpathdup(const char *fmt, ...)
diff --git a/path.c b/path.c
index a7ceea2..47753aa 100644
--- a/path.c
+++ b/path.c
@@ -70,19 +70,12 @@ static void vsnpath(struct strbuf *buf, const char *fmt, va_list args)
 	strbuf_cleanup_path(buf);
 }
 
-char *git_snpath(char *buf, size_t n, const char *fmt, ...)
+void strbuf_git_path(struct strbuf *sb, const char *fmt, ...)
 {
-	struct strbuf sb = STRBUF_INIT;
 	va_list args;
 	va_start(args, fmt);
-	vsnpath(&sb, fmt, args);
+	vsnpath(sb, fmt, args);
 	va_end(args);
-	if (sb.len >= n)
-		strlcpy(buf, bad_path, n);
-	else
-		memcpy(buf, sb.buf, sb.len + 1);
-	strbuf_release(&sb);
-	return buf;
 }
 
 char *git_pathdup(const char *fmt, ...)
diff --git a/refs.c b/refs.c
index 23617e0..5ed991b 100644
--- a/refs.c
+++ b/refs.c
@@ -1444,7 +1444,11 @@ static int resolve_missing_loose_ref(const char *refname,
 }
 
 /* This function needs to return a meaningful errno on failure */
-const char *resolve_ref_unsafe(const char *refname, int resolve_flags, unsigned char *sha1, int *flags)
+static const char *resolve_ref_unsafe_1(const char *refname,
+					int resolve_flags,
+					unsigned char *sha1,
+					int *flags,
+					struct strbuf *sb_path)
 {
 	int depth = MAXDEPTH;
 	ssize_t len;
@@ -1475,7 +1479,7 @@ const char *resolve_ref_unsafe(const char *refname, int resolve_flags, unsigned
 		bad_name = 1;
 	}
 	for (;;) {
-		char path[PATH_MAX];
+		const char *path;
 		struct stat st;
 		char *buf;
 		int fd;
@@ -1485,7 +1489,9 @@ const char *resolve_ref_unsafe(const char *refname, int resolve_flags, unsigned
 			return NULL;
 		}
 
-		git_snpath(path, sizeof(path), "%s", refname);
+		strbuf_reset(sb_path);
+		strbuf_git_path(sb_path, "%s", refname);
+		path = sb_path->buf;
 
 		/*
 		 * We might have to loop back here to avoid a race
@@ -1612,6 +1618,16 @@ const char *resolve_ref_unsafe(const char *refname, int resolve_flags, unsigned
 	}
 }
 
+const char *resolve_ref_unsafe(const char *refname, int resolve_flags,
+			       unsigned char *sha1, int *flags)
+{
+	struct strbuf sb_path = STRBUF_INIT;
+	const char *ret = resolve_ref_unsafe_1(refname, resolve_flags,
+					       sha1, flags, &sb_path);
+	strbuf_release(&sb_path);
+	return ret;
+}
+
 char *resolve_refdup(const char *ref, int resolve_flags, unsigned char *sha1, int *flags)
 {
 	const char *ret = resolve_ref_unsafe(ref, resolve_flags, sha1, flags);
@@ -2941,11 +2957,15 @@ static int copy_msg(char *buf, const char *msg)
 }
 
 /* This function must set a meaningful errno on failure */
-int log_ref_setup(const char *refname, char *logfile, int bufsize)
+int log_ref_setup(const char *refname, struct strbuf *sb_logfile)
 {
 	int logfd, oflags = O_APPEND | O_WRONLY;
+	char *logfile;
 
-	git_snpath(logfile, bufsize, "logs/%s", refname);
+	strbuf_git_path(sb_logfile, "logs/%s", refname);
+	logfile = sb_logfile->buf;
+	/* make sure the rest of the function can't change "logfile" */
+	sb_logfile = NULL;
 	if (log_all_ref_updates &&
 	    (starts_with(refname, "refs/heads/") ||
 	     starts_with(refname, "refs/remotes/") ||
@@ -2990,22 +3010,26 @@ int log_ref_setup(const char *refname, char *logfile, int bufsize)
 	return 0;
 }
 
-static int log_ref_write(const char *refname, const unsigned char *old_sha1,
-			 const unsigned char *new_sha1, const char *msg)
+static int log_ref_write_1(const char *refname, const unsigned char *old_sha1,
+			   const unsigned char *new_sha1, const char *msg,
+			   struct strbuf *sb_log_file)
 {
 	int logfd, result, written, oflags = O_APPEND | O_WRONLY;
 	unsigned maxlen, len;
 	int msglen;
-	char log_file[PATH_MAX];
+	const char *log_file;
 	char *logrec;
 	const char *committer;
 
 	if (log_all_ref_updates < 0)
 		log_all_ref_updates = !is_bare_repository();
 
-	result = log_ref_setup(refname, log_file, sizeof(log_file));
+	result = log_ref_setup(refname, sb_log_file);
 	if (result)
 		return result;
+	log_file = sb_log_file->buf;
+	/* make sure the rest of the function can't change "log_file" */
+	sb_log_file = NULL;
 
 	logfd = open(log_file, oflags);
 	if (logfd < 0)
@@ -3038,6 +3062,15 @@ static int log_ref_write(const char *refname, const unsigned char *old_sha1,
 	return 0;
 }
 
+static int log_ref_write(const char *refname, const unsigned char *old_sha1,
+			 const unsigned char *new_sha1, const char *msg)
+{
+	struct strbuf sb = STRBUF_INIT;
+	int ret = log_ref_write_1(refname, old_sha1, new_sha1, msg, &sb);
+	strbuf_release(&sb);
+	return ret;
+}
+
 int is_branch(const char *refname)
 {
 	return !strcmp(refname, "HEAD") || starts_with(refname, "refs/heads/");
diff --git a/refs.h b/refs.h
index 2bc3556..1f88220 100644
--- a/refs.h
+++ b/refs.h
@@ -210,7 +210,7 @@ extern void unlock_ref(struct ref_lock *lock);
 /*
  * Setup reflog before using. Set errno to something meaningful on failure.
  */
-int log_ref_setup(const char *refname, char *logfile, int bufsize);
+int log_ref_setup(const char *refname, struct strbuf *logfile);
 
 /** Reads log for the value of ref during at_time. **/
 extern int read_ref_at(const char *refname, unsigned int flags,
-- 
2.1.0.rc0.78.gc0d8480

[PATCH 04/34] path.c: rename vsnpath() to do_git_path()

[Nguyễn Thái Ngọc Duy]

The name vsnpath() gives an impression that this is general path
handling function. It's not. This is the underlying implementation of
git_path(), git_pathdup() and strbuf_git_path() which will prefix
$GIT_DIR in the result string.

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
---
 path.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/path.c b/path.c
index 47753aa..6991103 100644
--- a/path.c
+++ b/path.c
@@ -60,7 +60,7 @@ char *mksnpath(char *buf, size_t n, const char *fmt, ...)
 	return cleanup_path(buf);
 }
 
-static void vsnpath(struct strbuf *buf, const char *fmt, va_list args)
+static void do_git_path(struct strbuf *buf, const char *fmt, va_list args)
 {
 	const char *git_dir = get_git_dir();
 	strbuf_addstr(buf, git_dir);
@@ -74,7 +74,7 @@ void strbuf_git_path(struct strbuf *sb, const char *fmt, ...)
 {
 	va_list args;
 	va_start(args, fmt);
-	vsnpath(sb, fmt, args);
+	do_git_path(sb, fmt, args);
 	va_end(args);
 }
 
@@ -83,7 +83,7 @@ char *git_pathdup(const char *fmt, ...)
 	struct strbuf path = STRBUF_INIT;
 	va_list args;
 	va_start(args, fmt);
-	vsnpath(&path, fmt, args);
+	do_git_path(&path, fmt, args);
 	va_end(args);
 	return strbuf_detach(&path, NULL);
 }
@@ -114,7 +114,7 @@ const char *git_path(const char *fmt, ...)
 	struct strbuf *pathname = get_pathname();
 	va_list args;
 	va_start(args, fmt);
-	vsnpath(pathname, fmt, args);
+	do_git_path(pathname, fmt, args);
 	va_end(args);
 	return pathname->buf;
 }
-- 
2.1.0.rc0.78.gc0d8480

[PATCH 05/34] path.c: group git_path(), git_pathdup() and strbuf_git_path() together

[Nguyễn Thái Ngọc Duy]

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
---
 path.c | 20 ++++++++++----------
 1 file changed, 10 insertions(+), 10 deletions(-)

diff --git a/path.c b/path.c
index 6991103..df0f75b 100644
--- a/path.c
+++ b/path.c
@@ -78,6 +78,16 @@ void strbuf_git_path(struct strbuf *sb, const char *fmt, ...)
 	va_end(args);
 }
 
+const char *git_path(const char *fmt, ...)
+{
+	struct strbuf *pathname = get_pathname();
+	va_list args;
+	va_start(args, fmt);
+	do_git_path(pathname, fmt, args);
+	va_end(args);
+	return pathname->buf;
+}
+
 char *git_pathdup(const char *fmt, ...)
 {
 	struct strbuf path = STRBUF_INIT;
@@ -109,16 +119,6 @@ const char *mkpath(const char *fmt, ...)
 	return cleanup_path(pathname->buf);
 }
 
-const char *git_path(const char *fmt, ...)
-{
-	struct strbuf *pathname = get_pathname();
-	va_list args;
-	va_start(args, fmt);
-	do_git_path(pathname, fmt, args);
-	va_end(args);
-	return pathname->buf;
-}
-
 void home_config_paths(char **global, char **xdg, char *file)
 {
 	char *xdg_home = getenv("XDG_CONFIG_HOME");
-- 
2.1.0.rc0.78.gc0d8480

[PATCH 06/34] git_path(): be aware of file relocation in $GIT_DIR

[Nguyễn Thái Ngọc Duy]

We allow the user to relocate certain paths out of $GIT_DIR via
environment variables, e.g. GIT_OBJECT_DIRECTORY, GIT_INDEX_FILE and
GIT_GRAFT_FILE. Callers are not supposed to use git_path() or
git_pathdup() to get those paths. Instead they must use
get_object_directory(), get_index_file() and get_graft_file()
respectively. This is inconvenient and could be missed in review (for
example, there's git_path("objects/info/alternates") somewhere in
sha1_file.c).

This patch makes git_path() and git_pathdup() understand those
environment variables. So if you set GIT_OBJECT_DIRECTORY to /foo/bar,
git_path("objects/abc") should return /foo/bar/abc. The same is done
for the two remaining env variables.

"git rev-parse --git-path" is the wrapper for script use.

This patch kinda reverts a0279e1 (setup_git_env: use git_pathdup
instead of xmalloc + sprintf - 2014-06-19) because using git_pathdup
here would result in infinite recursion:

  setup_git_env() -> git_pathdup("objects") -> .. -> adjust_git_path()
  -> get_object_directory() -> oops, git_object_directory is NOT set
  yet -> setup_git_env()

I wanted to make git_pathdup_literal() that skips adjust_git_path().
But that won't work because later on when $GIT_COMMON_DIR is
introduced, git_pathdup_literal("objects") needs adjust_git_path() to
replace $GIT_DIR with $GIT_COMMON_DIR.

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
---
 Documentation/git-rev-parse.txt |  7 ++++++
 builtin/rev-parse.c             |  7 ++++++
 cache.h                         |  1 +
 environment.c                   | 19 +++++++++++-----
 path.c                          | 49 +++++++++++++++++++++++++++++++++++++++--
 t/t0060-path-utils.sh           | 19 ++++++++++++++++
 6 files changed, 95 insertions(+), 7 deletions(-)

diff --git a/Documentation/git-rev-parse.txt b/Documentation/git-rev-parse.txt
index d6de42f..2103bbf 100644
--- a/Documentation/git-rev-parse.txt
+++ b/Documentation/git-rev-parse.txt
@@ -233,6 +233,13 @@ print a message to stderr and exit with nonzero status.
 	repository.  If <path> is a gitfile then the resolved path
 	to the real repository is printed.
 
+--git-path <path>::
+	Resolve "$GIT_DIR/<path>" and takes other path relocation
+	variables such as $GIT_OBJECT_DIRECTORY,
+	$GIT_INDEX_FILE... into account. For example, if
+	$GIT_OBJECT_DIRECTORY is set to /foo/bar then "git rev-parse
+	--git-path objects/abc" returns /foo/bar/abc.
+
 --show-cdup::
 	When the command is invoked from a subdirectory, show the
 	path of the top-level directory relative to the current
diff --git a/builtin/rev-parse.c b/builtin/rev-parse.c
index 35d3c43..4cd44aa 100644
--- a/builtin/rev-parse.c
+++ b/builtin/rev-parse.c
@@ -533,6 +533,13 @@ int cmd_rev_parse(int argc, const char **argv, const char *prefix)
 	for (i = 1; i < argc; i++) {
 		const char *arg = argv[i];
 
+		if (!strcmp(arg, "--git-path")) {
+			if (!argv[i + 1])
+				die("--git-path requires an argument");
+			puts(git_path("%s", argv[i + 1]));
+			i++;
+			continue;
+		}
 		if (as_is) {
 			if (show_file(arg, output_prefix) && as_is < 2)
 				verify_filename(prefix, arg, 0);
diff --git a/cache.h b/cache.h
index 56643cf..7da2ffb 100644
--- a/cache.h
+++ b/cache.h
@@ -617,6 +617,7 @@ extern int fsync_object_files;
 extern int core_preload_index;
 extern int core_apply_sparse_checkout;
 extern int precomposed_unicode;
+extern int git_db_env, git_index_env, git_graft_env;
 
 /*
  * The character that begins a commented line in user-editable file
diff --git a/environment.c b/environment.c
index 565f652..fee12a6 100644
--- a/environment.c
+++ b/environment.c
@@ -83,6 +83,7 @@ static size_t namespace_len;
 
 static const char *git_dir;
 static char *git_object_dir, *git_index_file, *git_graft_file;
+int git_db_env, git_index_env, git_graft_env;
 
 /*
  * Repository-local GIT_* environment variables; see cache.h for details.
@@ -124,10 +125,18 @@ static char *expand_namespace(const char *raw_namespace)
 	return strbuf_detach(&buf, NULL);
 }
 
-static char *git_path_from_env(const char *envvar, const char *path)
+static char *git_path_from_env(const char *envvar, const char *path,
+			       int *fromenv)
 {
 	const char *value = getenv(envvar);
-	return value ? xstrdup(value) : git_pathdup("%s", path);
+	if (!value) {
+		char *buf = xmalloc(strlen(git_dir) + strlen(path) + 2);
+		sprintf(buf, "%s/%s", git_dir, path);
+		return buf;
+	}
+	if (fromenv)
+		*fromenv = 1;
+	return xstrdup(value);
 }
 
 static void setup_git_env(void)
@@ -140,9 +149,9 @@ static void setup_git_env(void)
 		git_dir = DEFAULT_GIT_DIR_ENVIRONMENT;
 	gitfile = read_gitfile(git_dir);
 	git_dir = xstrdup(gitfile ? gitfile : git_dir);
-	git_object_dir = git_path_from_env(DB_ENVIRONMENT, "objects");
-	git_index_file = git_path_from_env(INDEX_ENVIRONMENT, "index");
-	git_graft_file = git_path_from_env(GRAFT_ENVIRONMENT, "info/grafts");
+	git_object_dir = git_path_from_env(DB_ENVIRONMENT, "objects", &git_db_env);
+	git_index_file = git_path_from_env(INDEX_ENVIRONMENT, "index", &git_index_env);
+	git_graft_file = git_path_from_env(GRAFT_ENVIRONMENT, "info/grafts", &git_graft_env);
 	if (getenv(NO_REPLACE_OBJECTS_ENVIRONMENT))
 		check_replace_refs = 0;
 	namespace = expand_namespace(getenv(GIT_NAMESPACE_ENVIRONMENT));
diff --git a/path.c b/path.c
index df0f75b..4910783 100644
--- a/path.c
+++ b/path.c
@@ -60,13 +60,58 @@ char *mksnpath(char *buf, size_t n, const char *fmt, ...)
 	return cleanup_path(buf);
 }
 
+static int dir_prefix(const char *buf, const char *dir)
+{
+	int len = strlen(dir);
+	return !strncmp(buf, dir, len) &&
+		(is_dir_sep(buf[len]) || buf[len] == '\0');
+}
+
+/* $buf =~ m|$dir/+$file| but without regex */
+static int is_dir_file(const char *buf, const char *dir, const char *file)
+{
+	int len = strlen(dir);
+	if (strncmp(buf, dir, len) || !is_dir_sep(buf[len]))
+		return 0;
+	while (is_dir_sep(buf[len]))
+		len++;
+	return !strcmp(buf + len, file);
+}
+
+static void replace_dir(struct strbuf *buf, int len, const char *newdir)
+{
+	int newlen = strlen(newdir);
+	int need_sep = (buf->buf[len] && !is_dir_sep(buf->buf[len])) &&
+		!is_dir_sep(newdir[newlen - 1]);
+	if (need_sep)
+		len--;	 /* keep one char, to be replaced with '/'  */
+	strbuf_splice(buf, 0, len, newdir, newlen);
+	if (need_sep)
+		buf->buf[newlen] = '/';
+}
+
+static void adjust_git_path(struct strbuf *buf, int git_dir_len)
+{
+	const char *base = buf->buf + git_dir_len;
+	if (git_graft_env && is_dir_file(base, "info", "grafts"))
+		strbuf_splice(buf, 0, buf->len,
+			      get_graft_file(), strlen(get_graft_file()));
+	else if (git_index_env && !strcmp(base, "index"))
+		strbuf_splice(buf, 0, buf->len,
+			      get_index_file(), strlen(get_index_file()));
+	else if (git_db_env && dir_prefix(base, "objects"))
+		replace_dir(buf, git_dir_len + 7, get_object_directory());
+}
+
 static void do_git_path(struct strbuf *buf, const char *fmt, va_list args)
 {
-	const char *git_dir = get_git_dir();
-	strbuf_addstr(buf, git_dir);
+	int gitdir_len;
+	strbuf_addstr(buf, get_git_dir());
 	if (buf->len && !is_dir_sep(buf->buf[buf->len - 1]))
 		strbuf_addch(buf, '/');
+	gitdir_len = buf->len;
 	strbuf_vaddf(buf, fmt, args);
+	adjust_git_path(buf, gitdir_len);
 	strbuf_cleanup_path(buf);
 }
 
diff --git a/t/t0060-path-utils.sh b/t/t0060-path-utils.sh
index c0143a0..33d2818 100755
--- a/t/t0060-path-utils.sh
+++ b/t/t0060-path-utils.sh
@@ -19,6 +19,14 @@ relative_path() {
 	"test \"\$(test-path-utils relative_path '$1' '$2')\" = '$expected'"
 }
 
+test_git_path() {
+	test_expect_success "git-path $1 $2 => $3" "
+		$1 git rev-parse --git-path $2 >actual &&
+		echo $3 >expect &&
+		test_cmp expect actual
+	"
+}
+
 # On Windows, we are using MSYS's bash, which mangles the paths.
 # Absolute paths are anchored at the MSYS installation directory,
 # which means that the path / accounts for this many characters:
@@ -244,4 +252,15 @@ relative_path "<null>"		"<empty>"	./
 relative_path "<null>"		"<null>"	./
 relative_path "<null>"		/foo/a/b	./
 
+test_git_path A=B                info/grafts .git/info/grafts
+test_git_path GIT_GRAFT_FILE=foo info/grafts foo
+test_git_path GIT_GRAFT_FILE=foo info/////grafts foo
+test_git_path GIT_INDEX_FILE=foo index foo
+test_git_path GIT_INDEX_FILE=foo index/foo .git/index/foo
+test_git_path GIT_INDEX_FILE=foo index2 .git/index2
+test_expect_success 'setup fake objects directory foo' 'mkdir foo'
+test_git_path GIT_OBJECT_DIRECTORY=foo objects foo
+test_git_path GIT_OBJECT_DIRECTORY=foo objects/foo foo/foo
+test_git_path GIT_OBJECT_DIRECTORY=foo objects2 .git/objects2
+
 test_done
-- 
2.1.0.rc0.78.gc0d8480

[PATCH 07/34] *.sh: respect $GIT_INDEX_FILE

[Nguyễn Thái Ngọc Duy]

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
---
 git-pull.sh  | 2 +-
 git-stash.sh | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/git-pull.sh b/git-pull.sh
index 4d4fc77..ad44226 100755
--- a/git-pull.sh
+++ b/git-pull.sh
@@ -240,7 +240,7 @@ test true = "$rebase" && {
 	if ! git rev-parse -q --verify HEAD >/dev/null
 	then
 		# On an unborn branch
-		if test -f "$GIT_DIR/index"
+		if test -f "$(git rev-parse --git-path index)"
 		then
 			die "$(gettext "updating an unborn branch with changes added to the index")"
 		fi
diff --git a/git-stash.sh b/git-stash.sh
index d4cf818..b6d4b06 100755
--- a/git-stash.sh
+++ b/git-stash.sh
@@ -20,7 +20,7 @@ require_work_tree
 cd_to_toplevel
 
 TMP="$GIT_DIR/.git-stash.$$"
-TMPindex=${GIT_INDEX_FILE-"$GIT_DIR/index"}.stash.$$
+TMPindex=${GIT_INDEX_FILE-"$(git rev-parse --git-path index)"}.stash.$$
 trap 'rm -f "$TMP-"* "$TMPindex"' 0
 
 ref_stash=refs/stash
-- 
2.1.0.rc0.78.gc0d8480

[PATCH 08/34] reflog: avoid constructing .lock path with git_path

[Nguyễn Thái Ngọc Duy]

Among pathnames in $GIT_DIR, e.g. "index" or "packed-refs", we want to
automatically and silently map some of them to the $GIT_DIR of the
repository we are borrowing from via $GIT_COMMON_DIR mechanism.  When
we formulate the pathname for its lockfile, we want it to be in the
same location as its final destination.  "index" is not shared and
needs to remain in the borrowing repository, while "packed-refs" is
shared and needs to go to the borrowed repository.

git_path() could be taught about the ".lock" suffix and map
"index.lock" and "packed-refs.lock" the same way their basenames are
mapped, but instead the caller can help by asking where the basename
(e.g. "index") is mapped to git_path() and then appending ".lock"
after the mapping is done.

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
---
 builtin/reflog.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/builtin/reflog.c b/builtin/reflog.c
index 2d85d26..fb07c66 100644
--- a/builtin/reflog.c
+++ b/builtin/reflog.c
@@ -372,7 +372,7 @@ static int expire_reflog(const char *ref, const unsigned char *sha1, int unused,
 	if (!reflog_exists(ref))
 		goto finish;
 	if (!cmd->dry_run) {
-		newlog_path = git_pathdup("logs/%s.lock", ref);
+		newlog_path = mkpathdup("%s.lock", log_file);
 		cb.newlog = fopen(newlog_path, "w");
 	}
 
-- 
2.1.0.rc0.78.gc0d8480

[PATCH 09/34] fast-import: use git_path() for accessing .git dir instead of get_git_dir()

[Nguyễn Thái Ngọc Duy]

This allows git_path() to redirect info/fast-import to another place
if needed

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
---
 fast-import.c | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/fast-import.c b/fast-import.c
index 3018130..1b50923 100644
--- a/fast-import.c
+++ b/fast-import.c
@@ -3112,12 +3112,9 @@ static void parse_progress(void)
 
 static char* make_fast_import_path(const char *path)
 {
-	struct strbuf abs_path = STRBUF_INIT;
-
 	if (!relative_marks_paths || is_absolute_path(path))
 		return xstrdup(path);
-	strbuf_addf(&abs_path, "%s/info/fast-import/%s", get_git_dir(), path);
-	return strbuf_detach(&abs_path, NULL);
+	return xstrdup(git_path("info/fast-import/%s", path));
 }
 
 static void option_import_marks(const char *marks,
-- 
2.1.0.rc0.78.gc0d8480

[PATCH 10/34] commit: use SEQ_DIR instead of hardcoding "sequencer"

[Nguyễn Thái Ngọc Duy]

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
---
 builtin/commit.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/builtin/commit.c b/builtin/commit.c
index e108c53..3f02686 100644
--- a/builtin/commit.c
+++ b/builtin/commit.c
@@ -170,7 +170,7 @@ static void determine_whence(struct wt_status *s)
 		whence = FROM_MERGE;
 	else if (file_exists(git_path("CHERRY_PICK_HEAD"))) {
 		whence = FROM_CHERRY_PICK;
-		if (file_exists(git_path("sequencer")))
+		if (file_exists(git_path(SEQ_DIR)))
 			sequencer_in_use = 1;
 	}
 	else
-- 
2.1.0.rc0.78.gc0d8480

[PATCH 11/34] $GIT_COMMON_DIR: a new environment variable

[Nguyễn Thái Ngọc Duy]

This variable is intended to support multiple working directories
attached to a repository. Such a repository may have a main working
directory, created by either "git init" or "git clone" and one or more
linked working directories. These working directories and the main
repository share the same repository directory.

In linked working directories, $GIT_COMMON_DIR must be defined to point
to the real repository directory and $GIT_DIR points to an unused
subdirectory inside $GIT_COMMON_DIR. File locations inside the
repository are reorganized from the linked worktree view point:

 - worktree-specific such as HEAD, logs/HEAD, index, other top-level
   refs and unrecognized files are from $GIT_DIR.

 - the rest like objects, refs, info, hooks, packed-refs, shallow...
   are from $GIT_COMMON_DIR (except info/sparse-checkout, but that's
   a separate patch)

Scripts are supposed to retrieve paths in $GIT_DIR with "git rev-parse
--git-path", which will take care of "$GIT_DIR vs $GIT_COMMON_DIR"
business.

The redirection is done by git_path(), git_pathdup() and
strbuf_git_path(). The selected list of paths goes to $GIT_COMMON_DIR,
not the other way around in case a developer adds a new
worktree-specific file and it's accidentally promoted to be shared
across repositories (this includes unknown files added by third party
commands)

The list of known files that belong to $GIT_DIR are:

ADD_EDIT.patch BISECT_ANCESTORS_OK BISECT_EXPECTED_REV BISECT_LOG
BISECT_NAMES CHERRY_PICK_HEAD COMMIT_MSG FETCH_HEAD HEAD MERGE_HEAD
MERGE_MODE MERGE_RR NOTES_EDITMSG NOTES_MERGE_WORKTREE ORIG_HEAD
REVERT_HEAD SQUASH_MSG TAG_EDITMSG fast_import_crash_* logs/HEAD
next-index-* rebase-apply rebase-merge rsync-refs-* sequencer/*
shallow_*

Path mapping is NOT done for git_path_submodule(). Multi-checkouts are
not supported as submodules.

Helped-by: Jens Lehmann <Jens.Lehmann@web.de>
Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
---
 Documentation/git.txt                  |  8 ++++++
 Documentation/gitrepository-layout.txt | 45 +++++++++++++++++++++++++---------
 cache.h                                |  4 ++-
 environment.c                          | 29 ++++++++++++++++------
 path.c                                 | 34 +++++++++++++++++++++++++
 t/t0060-path-utils.sh                  | 16 ++++++++++++
 6 files changed, 117 insertions(+), 19 deletions(-)

diff --git a/Documentation/git.txt b/Documentation/git.txt
index afb48d3..96354af 100644
--- a/Documentation/git.txt
+++ b/Documentation/git.txt
@@ -809,6 +809,14 @@ Git so take care if using Cogito etc.
 	an explicit repository directory set via 'GIT_DIR' or on the
 	command line.
 
+'GIT_COMMON_DIR'::
+	If this variable is set to a path, non-worktree files that are
+	normally in $GIT_DIR will be taken from this path
+	instead. Worktree-specific files such as HEAD or index are
+	taken from $GIT_DIR. See linkgit:gitrepository-layout[5] for
+	details. This variable has lower precedence than other path
+	variables such as GIT_INDEX_FILE, GIT_OBJECT_DIRECTORY...
+
 Git Commits
 ~~~~~~~~~~~
 'GIT_AUTHOR_NAME'::
diff --git a/Documentation/gitrepository-layout.txt b/Documentation/gitrepository-layout.txt
index 79653f3..2b5966a 100644
--- a/Documentation/gitrepository-layout.txt
+++ b/Documentation/gitrepository-layout.txt
@@ -46,6 +46,9 @@ of incomplete object store is not suitable to be published for
 use with dumb transports but otherwise is OK as long as
 `objects/info/alternates` points at the object stores it
 borrows from.
++
+This directory is ignored if $GIT_COMMON_DIR is set and
+"$GIT_COMMON_DIR/objects" will be used instead.
 
 objects/[0-9a-f][0-9a-f]::
 	A newly created object is stored in its own file.
@@ -92,7 +95,8 @@ refs::
 	References are stored in subdirectories of this
 	directory.  The 'git prune' command knows to preserve
 	objects reachable from refs found in this directory and
-	its subdirectories.
+	its subdirectories. This directory is ignored if $GIT_COMMON_DIR
+	is set and "$GIT_COMMON_DIR/refs" will be used instead.
 
 refs/heads/`name`::
 	records tip-of-the-tree commit objects of branch `name`
@@ -114,7 +118,8 @@ refs/replace/`<obj-sha1>`::
 packed-refs::
 	records the same information as refs/heads/, refs/tags/,
 	and friends record in a more efficient way.  See
-	linkgit:git-pack-refs[1].
+	linkgit:git-pack-refs[1]. This file is ignored if $GIT_COMMON_DIR
+	is set and "$GIT_COMMON_DIR/packed-refs" will be used instead.
 
 HEAD::
 	A symref (see glossary) to the `refs/heads/` namespace
@@ -133,6 +138,11 @@ being a symref to point at the current branch.  Such a state
 is often called 'detached HEAD.'  See linkgit:git-checkout[1]
 for details.
 
+config::
+	Repository specific configuration file. This file is ignored
+	if $GIT_COMMON_DIR is set and "$GIT_COMMON_DIR/config" will be
+	used instead.
+
 branches::
 	A slightly deprecated way to store shorthands to be used
 	to specify a URL to 'git fetch', 'git pull' and 'git push'.
@@ -140,7 +150,10 @@ branches::
 	'name' can be given to these commands in place of
 	'repository' argument.  See the REMOTES section in
 	linkgit:git-fetch[1] for details.  This mechanism is legacy
-	and not likely to be found in modern repositories.
+	and not likely to be found in modern repositories. This
+	directory is ignored if $GIT_COMMON_DIR is set and
+	"$GIT_COMMON_DIR/branches" will be used instead.
+
 
 hooks::
 	Hooks are customization scripts used by various Git
@@ -149,7 +162,9 @@ hooks::
 	default.  To enable, the `.sample` suffix has to be
 	removed from the filename by renaming.
 	Read linkgit:githooks[5] for more details about
-	each hook.
+	each hook. This directory is ignored if $GIT_COMMON_DIR is set
+	and "$GIT_COMMON_DIR/hooks" will be used instead.
+
 
 index::
 	The current index file for the repository.  It is
@@ -161,7 +176,8 @@ sharedindex.<SHA-1>::
 
 info::
 	Additional information about the repository is recorded
-	in this directory.
+	in this directory. This directory is ignored if $GIT_COMMON_DIR
+	is set and "$GIT_COMMON_DIR/index" will be used instead.
 
 info/refs::
 	This file helps dumb transports discover what refs are
@@ -201,12 +217,15 @@ remotes::
 	when interacting with remote repositories via 'git fetch',
 	'git pull' and 'git push' commands.  See the REMOTES section
 	in linkgit:git-fetch[1] for details.  This mechanism is legacy
-	and not likely to be found in modern repositories.
+	and not likely to be found in modern repositories. This
+	directory is ignored if $GIT_COMMON_DIR is set and
+	"$GIT_COMMON_DIR/remotes" will be used instead.
 
 logs::
-	Records of changes made to refs are stored in this
-	directory.  See linkgit:git-update-ref[1]
-	for more information.
+	Records of changes made to refs are stored in this directory.
+	See linkgit:git-update-ref[1] for more information. This
+	directory is ignored if $GIT_COMMON_DIR is set and
+	"$GIT_COMMON_DIR/logs" will be used instead.
 
 logs/refs/heads/`name`::
 	Records all changes made to the branch tip named `name`.
@@ -217,10 +236,14 @@ logs/refs/tags/`name`::
 shallow::
 	This is similar to `info/grafts` but is internally used
 	and maintained by shallow clone mechanism.  See `--depth`
-	option to linkgit:git-clone[1] and linkgit:git-fetch[1].
+	option to linkgit:git-clone[1] and linkgit:git-fetch[1]. This
+	file is ignored if $GIT_COMMON_DIR is set and
+	"$GIT_COMMON_DIR/shallow" will be used instead.
 
 modules::
-	Contains the git-repositories of the submodules.
+	Contains the git-repositories of the submodules. This
+	directory is ignored if $GIT_COMMON_DIR is set and
+	"$GIT_COMMON_DIR/modules" will be used instead.
 
 SEE ALSO
 --------
diff --git a/cache.h b/cache.h
index 7da2ffb..bce1a7d 100644
--- a/cache.h
+++ b/cache.h
@@ -377,6 +377,7 @@ static inline enum object_type object_type(unsigned int mode)
 
 /* Double-check local_repo_env below if you add to this list. */
 #define GIT_DIR_ENVIRONMENT "GIT_DIR"
+#define GIT_COMMON_DIR_ENVIRONMENT "GIT_COMMON_DIR"
 #define GIT_NAMESPACE_ENVIRONMENT "GIT_NAMESPACE"
 #define GIT_WORK_TREE_ENVIRONMENT "GIT_WORK_TREE"
 #define GIT_PREFIX_ENVIRONMENT "GIT_PREFIX"
@@ -430,6 +431,7 @@ extern int is_inside_git_dir(void);
 extern char *git_work_tree_cfg;
 extern int is_inside_work_tree(void);
 extern const char *get_git_dir(void);
+extern const char *get_git_common_dir(void);
 extern int is_git_directory(const char *path);
 extern char *get_object_directory(void);
 extern char *get_index_file(void);
@@ -617,7 +619,7 @@ extern int fsync_object_files;
 extern int core_preload_index;
 extern int core_apply_sparse_checkout;
 extern int precomposed_unicode;
-extern int git_db_env, git_index_env, git_graft_env;
+extern int git_db_env, git_index_env, git_graft_env, git_common_dir_env;
 
 /*
  * The character that begins a commented line in user-editable file
diff --git a/environment.c b/environment.c
index fee12a6..050f160 100644
--- a/environment.c
+++ b/environment.c
@@ -81,9 +81,9 @@ static char *work_tree;
 static const char *namespace;
 static size_t namespace_len;
 
-static const char *git_dir;
+static const char *git_dir, *git_common_dir;
 static char *git_object_dir, *git_index_file, *git_graft_file;
-int git_db_env, git_index_env, git_graft_env;
+int git_db_env, git_index_env, git_graft_env, git_common_dir_env;
 
 /*
  * Repository-local GIT_* environment variables; see cache.h for details.
@@ -101,6 +101,7 @@ const char * const local_repo_env[] = {
 	NO_REPLACE_OBJECTS_ENVIRONMENT,
 	GIT_PREFIX_ENVIRONMENT,
 	GIT_SHALLOW_FILE_ENVIRONMENT,
+	GIT_COMMON_DIR_ENVIRONMENT,
 	NULL
 };
 
@@ -125,8 +126,8 @@ static char *expand_namespace(const char *raw_namespace)
 	return strbuf_detach(&buf, NULL);
 }
 
-static char *git_path_from_env(const char *envvar, const char *path,
-			       int *fromenv)
+static char *git_path_from_env(const char *envvar, const char *git_dir,
+			       const char *path, int *fromenv)
 {
 	const char *value = getenv(envvar);
 	if (!value) {
@@ -149,9 +150,18 @@ static void setup_git_env(void)
 		git_dir = DEFAULT_GIT_DIR_ENVIRONMENT;
 	gitfile = read_gitfile(git_dir);
 	git_dir = xstrdup(gitfile ? gitfile : git_dir);
-	git_object_dir = git_path_from_env(DB_ENVIRONMENT, "objects", &git_db_env);
-	git_index_file = git_path_from_env(INDEX_ENVIRONMENT, "index", &git_index_env);
-	git_graft_file = git_path_from_env(GRAFT_ENVIRONMENT, "info/grafts", &git_graft_env);
+	git_common_dir = getenv(GIT_COMMON_DIR_ENVIRONMENT);
+	if (git_common_dir) {
+		git_common_dir_env = 1;
+		git_common_dir = xstrdup(git_common_dir);
+	} else
+		git_common_dir = git_dir;
+	git_object_dir = git_path_from_env(DB_ENVIRONMENT, git_common_dir,
+					   "objects", &git_db_env);
+	git_index_file = git_path_from_env(INDEX_ENVIRONMENT, git_dir,
+					   "index", &git_index_env);
+	git_graft_file = git_path_from_env(GRAFT_ENVIRONMENT, git_common_dir,
+					   "info/grafts", &git_graft_env);
 	if (getenv(NO_REPLACE_OBJECTS_ENVIRONMENT))
 		check_replace_refs = 0;
 	namespace = expand_namespace(getenv(GIT_NAMESPACE_ENVIRONMENT));
@@ -174,6 +184,11 @@ const char *get_git_dir(void)
 	return git_dir;
 }
 
+const char *get_git_common_dir(void)
+{
+	return git_common_dir;
+}
+
 const char *get_git_namespace(void)
 {
 	if (!namespace)
diff --git a/path.c b/path.c
index 4910783..94db501 100644
--- a/path.c
+++ b/path.c
@@ -90,6 +90,38 @@ static void replace_dir(struct strbuf *buf, int len, const char *newdir)
 		buf->buf[newlen] = '/';
 }
 
+static const char *common_list[] = {
+	"/branches", "/hooks", "/info", "/logs", "/lost-found", "/modules",
+	"/objects", "/refs", "/remotes", "/rr-cache", "/svn",
+	"config", "gc.pid", "packed-refs", "shallow",
+	NULL
+};
+
+static void update_common_dir(struct strbuf *buf, int git_dir_len)
+{
+	char *base = buf->buf + git_dir_len;
+	const char **p;
+
+	if (is_dir_file(base, "logs", "HEAD"))
+		return;	/* keep this in $GIT_DIR */
+	for (p = common_list; *p; p++) {
+		const char *path = *p;
+		int is_dir = 0;
+		if (*path == '/') {
+			path++;
+			is_dir = 1;
+		}
+		if (is_dir && dir_prefix(base, path)) {
+			replace_dir(buf, git_dir_len, get_git_common_dir());
+			return;
+		}
+		if (!is_dir && !strcmp(base, path)) {
+			replace_dir(buf, git_dir_len, get_git_common_dir());
+			return;
+		}
+	}
+}
+
 static void adjust_git_path(struct strbuf *buf, int git_dir_len)
 {
 	const char *base = buf->buf + git_dir_len;
@@ -101,6 +133,8 @@ static void adjust_git_path(struct strbuf *buf, int git_dir_len)
 			      get_index_file(), strlen(get_index_file()));
 	else if (git_db_env && dir_prefix(base, "objects"))
 		replace_dir(buf, git_dir_len + 7, get_object_directory());
+	else if (git_common_dir_env)
+		update_common_dir(buf, git_dir_len);
 }
 
 static void do_git_path(struct strbuf *buf, const char *fmt, va_list args)
diff --git a/t/t0060-path-utils.sh b/t/t0060-path-utils.sh
index 33d2818..f5d6f80 100755
--- a/t/t0060-path-utils.sh
+++ b/t/t0060-path-utils.sh
@@ -262,5 +262,21 @@ test_expect_success 'setup fake objects directory foo' 'mkdir foo'
 test_git_path GIT_OBJECT_DIRECTORY=foo objects foo
 test_git_path GIT_OBJECT_DIRECTORY=foo objects/foo foo/foo
 test_git_path GIT_OBJECT_DIRECTORY=foo objects2 .git/objects2
+test_expect_success 'setup common repository' 'git --git-dir=bar init'
+test_git_path GIT_COMMON_DIR=bar index                    .git/index
+test_git_path GIT_COMMON_DIR=bar HEAD                     .git/HEAD
+test_git_path GIT_COMMON_DIR=bar logs/HEAD                .git/logs/HEAD
+test_git_path GIT_COMMON_DIR=bar objects                  bar/objects
+test_git_path GIT_COMMON_DIR=bar objects/bar              bar/objects/bar
+test_git_path GIT_COMMON_DIR=bar info/exclude             bar/info/exclude
+test_git_path GIT_COMMON_DIR=bar info/grafts              bar/info/grafts
+test_git_path GIT_COMMON_DIR=bar remotes/bar              bar/remotes/bar
+test_git_path GIT_COMMON_DIR=bar branches/bar             bar/branches/bar
+test_git_path GIT_COMMON_DIR=bar logs/refs/heads/master   bar/logs/refs/heads/master
+test_git_path GIT_COMMON_DIR=bar refs/heads/master        bar/refs/heads/master
+test_git_path GIT_COMMON_DIR=bar hooks/me                 bar/hooks/me
+test_git_path GIT_COMMON_DIR=bar config                   bar/config
+test_git_path GIT_COMMON_DIR=bar packed-refs              bar/packed-refs
+test_git_path GIT_COMMON_DIR=bar shallow                  bar/shallow
 
 test_done
-- 
2.1.0.rc0.78.gc0d8480

[PATCH 12/34] git-sh-setup.sh: use rev-parse --git-path to get $GIT_DIR/objects

[Nguyễn Thái Ngọc Duy]

If $GIT_COMMON_DIR is set, $GIT_OBJECT_DIRECTORY should be
$GIT_COMMON_DIR/objects, not $GIT_DIR/objects. Just let rev-parse
--git-path handle it.

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
---
 git-sh-setup.sh | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/git-sh-setup.sh b/git-sh-setup.sh
index d968760..94a5c6d 100644
--- a/git-sh-setup.sh
+++ b/git-sh-setup.sh
@@ -344,7 +344,7 @@ git_dir_init () {
 		echo >&2 "Unable to determine absolute path of git directory"
 		exit 1
 	}
-	: ${GIT_OBJECT_DIRECTORY="$GIT_DIR/objects"}
+	: ${GIT_OBJECT_DIRECTORY="$(git rev-parse --git-path objects)"}
 }
 
 if test -z "$NONGIT_OK"
-- 
2.1.0.rc0.78.gc0d8480

[PATCH 13/34] *.sh: avoid hardcoding $GIT_DIR/hooks/...

[Nguyễn Thái Ngọc Duy]

If $GIT_COMMON_DIR is set, it should be $GIT_COMMON_DIR/hooks/, not
$GIT_DIR/hooks/. Just let rev-parse --git-path handle it.

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
---
 git-am.sh                              | 22 +++++++++++-----------
 git-rebase--interactive.sh             |  6 +++---
 git-rebase--merge.sh                   |  6 ++----
 git-rebase.sh                          |  4 ++--
 templates/hooks--applypatch-msg.sample |  4 ++--
 templates/hooks--pre-applypatch.sample |  4 ++--
 6 files changed, 22 insertions(+), 24 deletions(-)

diff --git a/git-am.sh b/git-am.sh
index ee61a77..66803d1 100755
--- a/git-am.sh
+++ b/git-am.sh
@@ -810,10 +810,10 @@ To restore the original branch and stop patching run \"\$cmdline --abort\"."
 		continue
 	fi
 
-	if test -x "$GIT_DIR"/hooks/applypatch-msg
+	hook="$(git rev-parse --git-path hooks/applypatch-msg)"
+	if test -x "$hook"
 	then
-		"$GIT_DIR"/hooks/applypatch-msg "$dotest/final-commit" ||
-		stop_here $this
+		"$hook" "$dotest/final-commit" || stop_here $this
 	fi
 
 	if test -f "$dotest/final-commit"
@@ -887,9 +887,10 @@ did you forget to use 'git add'?"
 		stop_here_user_resolve $this
 	fi
 
-	if test -x "$GIT_DIR"/hooks/pre-applypatch
+	hook="$(git rev-parse --git-path hooks/pre-applypatch)"
+	if test -x "$hook"
 	then
-		"$GIT_DIR"/hooks/pre-applypatch || stop_here $this
+		"$hook" || stop_here $this
 	fi
 
 	tree=$(git write-tree) &&
@@ -916,18 +917,17 @@ did you forget to use 'git add'?"
 		echo "$(cat "$dotest/original-commit") $commit" >> "$dotest/rewritten"
 	fi
 
-	if test -x "$GIT_DIR"/hooks/post-applypatch
-	then
-		"$GIT_DIR"/hooks/post-applypatch
-	fi
+	hook="$(git rev-parse --git-path hooks/post-applypatch)"
+	test -x "$hook" && "$hook"
 
 	go_next
 done
 
 if test -s "$dotest"/rewritten; then
     git notes copy --for-rewrite=rebase < "$dotest"/rewritten
-    if test -x "$GIT_DIR"/hooks/post-rewrite; then
-	"$GIT_DIR"/hooks/post-rewrite rebase < "$dotest"/rewritten
+    hook="$(git rev-parse --git-path hooks/post-rewrite)"
+    if test -x "$hook"; then
+	"$hook" rebase < "$dotest"/rewritten
     fi
 fi
 
diff --git a/git-rebase--interactive.sh b/git-rebase--interactive.sh
index b64dd28..b32f797 100644
--- a/git-rebase--interactive.sh
+++ b/git-rebase--interactive.sh
@@ -642,9 +642,9 @@ do_next () {
 		git notes copy --for-rewrite=rebase < "$rewritten_list" ||
 		true # we don't care if this copying failed
 	} &&
-	if test -x "$GIT_DIR"/hooks/post-rewrite &&
-		test -s "$rewritten_list"; then
-		"$GIT_DIR"/hooks/post-rewrite rebase < "$rewritten_list"
+	hook="$(git rev-parse --git-path hooks/post-rewrite)"
+	if test -x "$hook" && test -s "$rewritten_list"; then
+		"$hook" rebase < "$rewritten_list"
 		true # we don't care if this hook failed
 	fi &&
 	warn "Successfully rebased and updated $head_name."
diff --git a/git-rebase--merge.sh b/git-rebase--merge.sh
index d3fb67d..2cc2a6d 100644
--- a/git-rebase--merge.sh
+++ b/git-rebase--merge.sh
@@ -94,10 +94,8 @@ finish_rb_merge () {
 	if test -s "$state_dir"/rewritten
 	then
 		git notes copy --for-rewrite=rebase <"$state_dir"/rewritten
-		if test -x "$GIT_DIR"/hooks/post-rewrite
-		then
-			"$GIT_DIR"/hooks/post-rewrite rebase <"$state_dir"/rewritten
-		fi
+		hook="$(git rev-parse --git-path hooks/post-rewrite)"
+		test -x "$hook" && "$hook" rebase <"$state_dir"/rewritten
 	fi
 	say All done.
 }
diff --git a/git-rebase.sh b/git-rebase.sh
index 55da9db..fb935a0 100755
--- a/git-rebase.sh
+++ b/git-rebase.sh
@@ -202,9 +202,9 @@ run_specific_rebase () {
 
 run_pre_rebase_hook () {
 	if test -z "$ok_to_skip_pre_rebase" &&
-	   test -x "$GIT_DIR/hooks/pre-rebase"
+	   test -x "$(git rev-parse --git-path hooks/pre-rebase)"
 	then
-		"$GIT_DIR/hooks/pre-rebase" ${1+"$@"} ||
+		"$(git rev-parse --git-path hooks/pre-rebase)" ${1+"$@"} ||
 		die "$(gettext "The pre-rebase hook refused to rebase.")"
 	fi
 }
diff --git a/templates/hooks--applypatch-msg.sample b/templates/hooks--applypatch-msg.sample
index 8b2a2fe..a5d7b84 100755
--- a/templates/hooks--applypatch-msg.sample
+++ b/templates/hooks--applypatch-msg.sample
@@ -10,6 +10,6 @@
 # To enable this hook, rename this file to "applypatch-msg".
 
 . git-sh-setup
-test -x "$GIT_DIR/hooks/commit-msg" &&
-	exec "$GIT_DIR/hooks/commit-msg" ${1+"$@"}
+commitmsg="$(git rev-parse --git-path hooks/commit-msg)"
+test -x "$commitmsg" && exec "$commitmsg" ${1+"$@"}
 :
diff --git a/templates/hooks--pre-applypatch.sample b/templates/hooks--pre-applypatch.sample
index b1f187c..4142082 100755
--- a/templates/hooks--pre-applypatch.sample
+++ b/templates/hooks--pre-applypatch.sample
@@ -9,6 +9,6 @@
 # To enable this hook, rename this file to "pre-applypatch".
 
 . git-sh-setup
-test -x "$GIT_DIR/hooks/pre-commit" &&
-	exec "$GIT_DIR/hooks/pre-commit" ${1+"$@"}
+precommit="$(git rev-parse --git-path hooks/pre-commit)"
+test -x "$precommit" && exec "$precommit" ${1+"$@"}
 :
-- 
2.1.0.rc0.78.gc0d8480

[PATCH 14/34] git-stash: avoid hardcoding $GIT_DIR/logs/....

[Nguyễn Thái Ngọc Duy]

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
---
 git-stash.sh | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/git-stash.sh b/git-stash.sh
index b6d4b06..6846b18 100755
--- a/git-stash.sh
+++ b/git-stash.sh
@@ -184,7 +184,7 @@ store_stash () {
 	fi
 
 	# Make sure the reflog for stash is kept.
-	: >>"$GIT_DIR/logs/$ref_stash"
+	: >>"$(git rev-parse --git-path logs/$ref_stash)"
 	git update-ref -m "$stash_msg" $ref_stash $w_commit
 	ret=$?
 	test $ret != 0 && test -z $quiet &&
@@ -259,7 +259,7 @@ save_stash () {
 		say "$(gettext "No local changes to save")"
 		exit 0
 	fi
-	test -f "$GIT_DIR/logs/$ref_stash" ||
+	test -f "$(git rev-parse --git-path logs/$ref_stash)" ||
 		clear_stash || die "$(gettext "Cannot initialize stash")"
 
 	create_stash "$stash_msg" $untracked
-- 
2.1.0.rc0.78.gc0d8480

[PATCH 15/34] setup.c: convert is_git_directory() to use strbuf

[Nguyễn Thái Ngọc Duy]

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
---
 setup.c | 37 +++++++++++++++++++++----------------
 1 file changed, 21 insertions(+), 16 deletions(-)

diff --git a/setup.c b/setup.c
index 979b13f..afd6742 100644
--- a/setup.c
+++ b/setup.c
@@ -238,31 +238,36 @@ void verify_non_filename(const char *prefix, const char *arg)
  */
 int is_git_directory(const char *suspect)
 {
-	char path[PATH_MAX];
-	size_t len = strlen(suspect);
+	struct strbuf path = STRBUF_INIT;
+	int ret = 0;
+	size_t len;
 
-	if (PATH_MAX <= len + strlen("/objects"))
-		die("Too long path: %.*s", 60, suspect);
-	strcpy(path, suspect);
+	strbuf_addstr(&path, suspect);
+	len = path.len;
 	if (getenv(DB_ENVIRONMENT)) {
 		if (access(getenv(DB_ENVIRONMENT), X_OK))
-			return 0;
+			goto done;
 	}
 	else {
-		strcpy(path + len, "/objects");
-		if (access(path, X_OK))
-			return 0;
+		strbuf_addstr(&path, "/objects");
+		if (access(path.buf, X_OK))
+			goto done;
 	}
 
-	strcpy(path + len, "/refs");
-	if (access(path, X_OK))
-		return 0;
+	strbuf_setlen(&path, len);
+	strbuf_addstr(&path, "/refs");
+	if (access(path.buf, X_OK))
+		goto done;
 
-	strcpy(path + len, "/HEAD");
-	if (validate_headref(path))
-		return 0;
+	strbuf_setlen(&path, len);
+	strbuf_addstr(&path, "/HEAD");
+	if (validate_headref(path.buf))
+		goto done;
 
-	return 1;
+	ret = 1;
+done:
+	strbuf_release(&path);
+	return ret;
 }
 
 int is_inside_git_dir(void)
-- 
2.1.0.rc0.78.gc0d8480

[PATCH 16/34] setup.c: detect $GIT_COMMON_DIR in is_git_directory()

[Nguyễn Thái Ngọc Duy]

If the file "$GIT_DIR/commondir" exists, it contains the value of
$GIT_COMMON_DIR.

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
---
 Documentation/gitrepository-layout.txt |  7 ++++++
 setup.c                                | 43 +++++++++++++++++++++++++++++-----
 2 files changed, 44 insertions(+), 6 deletions(-)

diff --git a/Documentation/gitrepository-layout.txt b/Documentation/gitrepository-layout.txt
index 2b5966a..2dc5667 100644
--- a/Documentation/gitrepository-layout.txt
+++ b/Documentation/gitrepository-layout.txt
@@ -240,6 +240,13 @@ shallow::
 	file is ignored if $GIT_COMMON_DIR is set and
 	"$GIT_COMMON_DIR/shallow" will be used instead.
 
+commondir::
+	If this file exists, $GIT_COMMON_DIR (see linkgit:git[1]) will
+	be set to the path specified in this file if it is not
+	explicitly set. If the specified path is relative, it is
+	relative to $GIT_DIR. The repository with commondir is
+	incomplete without the repository pointed by "commondir".
+
 modules::
 	Contains the git-repositories of the submodules. This
 	directory is ignored if $GIT_COMMON_DIR is set and
diff --git a/setup.c b/setup.c
index afd6742..6c52f75 100644
--- a/setup.c
+++ b/setup.c
@@ -224,6 +224,33 @@ void verify_non_filename(const char *prefix, const char *arg)
 	    "'git <command> [<revision>...] -- [<file>...]'", arg);
 }
 
+static void get_common_dir(struct strbuf *sb, const char *gitdir)
+{
+	struct strbuf data = STRBUF_INIT;
+	struct strbuf path = STRBUF_INIT;
+	const char *git_common_dir = getenv(GIT_COMMON_DIR_ENVIRONMENT);
+	if (git_common_dir) {
+		strbuf_addstr(sb, git_common_dir);
+		return;
+	}
+	strbuf_addf(&path, "%s/commondir", gitdir);
+	if (file_exists(path.buf)) {
+		if (strbuf_read_file(&data, path.buf, 0) <= 0)
+			die_errno(_("failed to read %s"), path.buf);
+		while (data.len && (data.buf[data.len - 1] == '\n' ||
+				    data.buf[data.len - 1] == '\r'))
+			data.len--;
+		data.buf[data.len] = '\0';
+		strbuf_reset(&path);
+		if (!is_absolute_path(data.buf))
+			strbuf_addf(&path, "%s/", gitdir);
+		strbuf_addbuf(&path, &data);
+		strbuf_addstr(sb, real_path(path.buf));
+	} else
+		strbuf_addstr(sb, gitdir);
+	strbuf_release(&data);
+	strbuf_release(&path);
+}
 
 /*
  * Test if it looks like we're at a git directory.
@@ -242,13 +269,22 @@ int is_git_directory(const char *suspect)
 	int ret = 0;
 	size_t len;
 
-	strbuf_addstr(&path, suspect);
+	/* Check worktree-related signatures */
+	strbuf_addf(&path, "%s/HEAD", suspect);
+	if (validate_headref(path.buf))
+		goto done;
+
+	strbuf_reset(&path);
+	get_common_dir(&path, suspect);
 	len = path.len;
+
+	/* Check non-worktree-related signatures */
 	if (getenv(DB_ENVIRONMENT)) {
 		if (access(getenv(DB_ENVIRONMENT), X_OK))
 			goto done;
 	}
 	else {
+		strbuf_setlen(&path, len);
 		strbuf_addstr(&path, "/objects");
 		if (access(path.buf, X_OK))
 			goto done;
@@ -259,11 +295,6 @@ int is_git_directory(const char *suspect)
 	if (access(path.buf, X_OK))
 		goto done;
 
-	strbuf_setlen(&path, len);
-	strbuf_addstr(&path, "/HEAD");
-	if (validate_headref(path.buf))
-		goto done;
-
 	ret = 1;
 done:
 	strbuf_release(&path);
-- 
2.1.0.rc0.78.gc0d8480

[PATCH 17/34] setup.c: convert check_repository_format_gently to use strbuf

[Nguyễn Thái Ngọc Duy]

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
---
 setup.c | 12 ++++++++----
 1 file changed, 8 insertions(+), 4 deletions(-)

diff --git a/setup.c b/setup.c
index 6c52f75..00a23e6 100644
--- a/setup.c
+++ b/setup.c
@@ -342,7 +342,9 @@ void setup_work_tree(void)
 
 static int check_repository_format_gently(const char *gitdir, int *nongit_ok)
 {
-	char repo_config[PATH_MAX+1];
+	struct strbuf sb = STRBUF_INIT;
+	const char *repo_config;
+	int ret = 0;
 
 	/*
 	 * git_config() can't be used here because it calls git_pathdup()
@@ -353,7 +355,8 @@ static int check_repository_format_gently(const char *gitdir, int *nongit_ok)
 	 * Use a gentler version of git_config() to check if this repo
 	 * is a good one.
 	 */
-	snprintf(repo_config, PATH_MAX, "%s/config", gitdir);
+	strbuf_addf(&sb, "%s/config", gitdir);
+	repo_config = sb.buf;
 	git_config_early(check_repository_format_version, NULL, repo_config);
 	if (GIT_REPO_VERSION < repository_format_version) {
 		if (!nongit_ok)
@@ -363,9 +366,10 @@ static int check_repository_format_gently(const char *gitdir, int *nongit_ok)
 			GIT_REPO_VERSION, repository_format_version);
 		warning("Please upgrade Git");
 		*nongit_ok = -1;
-		return -1;
+		ret = -1;
 	}
-	return 0;
+	strbuf_release(&sb);
+	return ret;
 }
 
 /*
-- 
2.1.0.rc0.78.gc0d8480

[PATCH 18/34] setup.c: detect $GIT_COMMON_DIR check_repository_format_gently()

[Nguyễn Thái Ngọc Duy]

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
---
 setup.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/setup.c b/setup.c
index 00a23e6..1d4f1aa 100644
--- a/setup.c
+++ b/setup.c
@@ -346,6 +346,10 @@ static int check_repository_format_gently(const char *gitdir, int *nongit_ok)
 	const char *repo_config;
 	int ret = 0;
 
+	get_common_dir(&sb, gitdir);
+	strbuf_addstr(&sb, "/config");
+	repo_config = sb.buf;
+
 	/*
 	 * git_config() can't be used here because it calls git_pathdup()
 	 * to get $GIT_CONFIG/config. That call will make setup_git_env()
@@ -355,8 +359,6 @@ static int check_repository_format_gently(const char *gitdir, int *nongit_ok)
 	 * Use a gentler version of git_config() to check if this repo
 	 * is a good one.
 	 */
-	strbuf_addf(&sb, "%s/config", gitdir);
-	repo_config = sb.buf;
 	git_config_early(check_repository_format_version, NULL, repo_config);
 	if (GIT_REPO_VERSION < repository_format_version) {
 		if (!nongit_ok)
-- 
2.1.0.rc0.78.gc0d8480

[PATCH 19/34] setup.c: support multi-checkout repo setup

[Nguyễn Thái Ngọc Duy]

The repo setup procedure is updated to detect $GIT_DIR/commondir and
set $GIT_COMMON_DIR properly.

The core.worktree is ignored when $GIT_COMMON_DIR is set. This is
because the config file is shared in multi-checkout setup, but
checkout directories _are_ different. Making core.worktree effective
in all checkouts mean it's back to a single checkout.

Helped-by: Johannes Sixt <j6t@kdbg.org>
Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
---
 Documentation/config.txt        |  2 ++
 Documentation/git-rev-parse.txt |  3 ++
 builtin/rev-parse.c             |  4 +++
 cache.h                         |  1 +
 environment.c                   |  8 ++---
 setup.c                         | 33 +++++++++++++-----
 t/t1501-worktree.sh             | 76 +++++++++++++++++++++++++++++++++++++++++
 t/t1510-repo-setup.sh           |  1 +
 trace.c                         |  1 +
 9 files changed, 115 insertions(+), 14 deletions(-)

diff --git a/Documentation/config.txt b/Documentation/config.txt
index 9220725..e1623ec 100644
--- a/Documentation/config.txt
+++ b/Documentation/config.txt
@@ -393,6 +393,8 @@ false), while all other repositories are assumed to be bare (bare
 
 core.worktree::
 	Set the path to the root of the working tree.
+	If GIT_COMMON_DIR environment variable is set, core.worktree
+	is ignored and not used for determining the root of working tree.
 	This can be overridden by the GIT_WORK_TREE environment
 	variable and the '--work-tree' command-line option.
 	The value can be an absolute path or relative to the path to
diff --git a/Documentation/git-rev-parse.txt b/Documentation/git-rev-parse.txt
index 2103bbf..97fc703 100644
--- a/Documentation/git-rev-parse.txt
+++ b/Documentation/git-rev-parse.txt
@@ -216,6 +216,9 @@ If `$GIT_DIR` is not defined and the current directory
 is not detected to lie in a Git repository or work tree
 print a message to stderr and exit with nonzero status.
 
+--git-common-dir::
+	Show `$GIT_COMMON_DIR` if defined, else `$GIT_DIR`.
+
 --is-inside-git-dir::
 	When the current working directory is below the repository
 	directory print "true", otherwise "false".
diff --git a/builtin/rev-parse.c b/builtin/rev-parse.c
index 4cd44aa..5799f35 100644
--- a/builtin/rev-parse.c
+++ b/builtin/rev-parse.c
@@ -762,6 +762,10 @@ int cmd_rev_parse(int argc, const char **argv, const char *prefix)
 				free(cwd);
 				continue;
 			}
+			if (!strcmp(arg, "--git-common-dir")) {
+				puts(get_git_common_dir());
+				continue;
+			}
 			if (!strcmp(arg, "--resolve-git-dir")) {
 				const char *gitdir = argv[++i];
 				if (!gitdir)
diff --git a/cache.h b/cache.h
index bce1a7d..9dc6ae0 100644
--- a/cache.h
+++ b/cache.h
@@ -437,6 +437,7 @@ extern char *get_object_directory(void);
 extern char *get_index_file(void);
 extern char *get_graft_file(void);
 extern int set_git_dir(const char *path);
+extern int get_common_dir(struct strbuf *sb, const char *gitdir);
 extern const char *get_git_namespace(void);
 extern const char *strip_namespace(const char *namespaced_ref);
 extern const char *get_git_work_tree(void);
diff --git a/environment.c b/environment.c
index 050f160..8351007 100644
--- a/environment.c
+++ b/environment.c
@@ -142,6 +142,7 @@ static char *git_path_from_env(const char *envvar, const char *git_dir,
 
 static void setup_git_env(void)
 {
+	struct strbuf sb = STRBUF_INIT;
 	const char *gitfile;
 	const char *shallow_file;
 
@@ -150,12 +151,9 @@ static void setup_git_env(void)
 		git_dir = DEFAULT_GIT_DIR_ENVIRONMENT;
 	gitfile = read_gitfile(git_dir);
 	git_dir = xstrdup(gitfile ? gitfile : git_dir);
-	git_common_dir = getenv(GIT_COMMON_DIR_ENVIRONMENT);
-	if (git_common_dir) {
+	if (get_common_dir(&sb, git_dir))
 		git_common_dir_env = 1;
-		git_common_dir = xstrdup(git_common_dir);
-	} else
-		git_common_dir = git_dir;
+	git_common_dir = strbuf_detach(&sb, NULL);
 	git_object_dir = git_path_from_env(DB_ENVIRONMENT, git_common_dir,
 					   "objects", &git_db_env);
 	git_index_file = git_path_from_env(INDEX_ENVIRONMENT, git_dir,
diff --git a/setup.c b/setup.c
index 1d4f1aa..b99bdd3 100644
--- a/setup.c
+++ b/setup.c
@@ -224,14 +224,15 @@ void verify_non_filename(const char *prefix, const char *arg)
 	    "'git <command> [<revision>...] -- [<file>...]'", arg);
 }
 
-static void get_common_dir(struct strbuf *sb, const char *gitdir)
+int get_common_dir(struct strbuf *sb, const char *gitdir)
 {
 	struct strbuf data = STRBUF_INIT;
 	struct strbuf path = STRBUF_INIT;
 	const char *git_common_dir = getenv(GIT_COMMON_DIR_ENVIRONMENT);
+	int ret = 0;
 	if (git_common_dir) {
 		strbuf_addstr(sb, git_common_dir);
-		return;
+		return 1;
 	}
 	strbuf_addf(&path, "%s/commondir", gitdir);
 	if (file_exists(path.buf)) {
@@ -246,10 +247,12 @@ static void get_common_dir(struct strbuf *sb, const char *gitdir)
 			strbuf_addf(&path, "%s/", gitdir);
 		strbuf_addbuf(&path, &data);
 		strbuf_addstr(sb, real_path(path.buf));
+		ret = 1;
 	} else
 		strbuf_addstr(sb, gitdir);
 	strbuf_release(&data);
 	strbuf_release(&path);
+	return ret;
 }
 
 /*
@@ -340,13 +343,26 @@ void setup_work_tree(void)
 	initialized = 1;
 }
 
+static int check_repo_format(const char *var, const char *value, void *cb)
+{
+	if (strcmp(var, "core.repositoryformatversion") == 0)
+		repository_format_version = git_config_int(var, value);
+	else if (strcmp(var, "core.sharedrepository") == 0)
+		shared_repository = git_config_perm(var, value);
+	return 0;
+}
+
 static int check_repository_format_gently(const char *gitdir, int *nongit_ok)
 {
 	struct strbuf sb = STRBUF_INIT;
 	const char *repo_config;
+	config_fn_t fn;
 	int ret = 0;
 
-	get_common_dir(&sb, gitdir);
+	if (get_common_dir(&sb, gitdir))
+		fn = check_repo_format;
+	else
+		fn = check_repository_format_version;
 	strbuf_addstr(&sb, "/config");
 	repo_config = sb.buf;
 
@@ -359,7 +375,7 @@ static int check_repository_format_gently(const char *gitdir, int *nongit_ok)
 	 * Use a gentler version of git_config() to check if this repo
 	 * is a good one.
 	 */
-	git_config_early(check_repository_format_version, NULL, repo_config);
+	git_config_early(fn, NULL, repo_config);
 	if (GIT_REPO_VERSION < repository_format_version) {
 		if (!nongit_ok)
 			die ("Expected git repo version <= %d, found %d",
@@ -841,11 +857,10 @@ int git_config_perm(const char *var, const char *value)
 
 int check_repository_format_version(const char *var, const char *value, void *cb)
 {
-	if (strcmp(var, "core.repositoryformatversion") == 0)
-		repository_format_version = git_config_int(var, value);
-	else if (strcmp(var, "core.sharedrepository") == 0)
-		shared_repository = git_config_perm(var, value);
-	else if (strcmp(var, "core.bare") == 0) {
+	int ret = check_repo_format(var, value, cb);
+	if (ret)
+		return ret;
+	if (strcmp(var, "core.bare") == 0) {
 		is_bare_repository_cfg = git_config_bool(var, value);
 		if (is_bare_repository_cfg == 1)
 			inside_work_tree = -1;
diff --git a/t/t1501-worktree.sh b/t/t1501-worktree.sh
index 8f36aa9..4df7a2f 100755
--- a/t/t1501-worktree.sh
+++ b/t/t1501-worktree.sh
@@ -346,4 +346,80 @@ test_expect_success 'relative $GIT_WORK_TREE and git subprocesses' '
 	test_cmp expected actual
 '
 
+test_expect_success 'Multi-worktree setup' '
+	mkdir work &&
+	mkdir -p repo.git/repos/foo &&
+	cp repo.git/HEAD repo.git/index repo.git/repos/foo &&
+	sane_unset GIT_DIR GIT_CONFIG GIT_WORK_TREE
+'
+
+test_expect_success 'GIT_DIR set (1)' '
+	echo "gitdir: repo.git/repos/foo" >gitfile &&
+	echo ../.. >repo.git/repos/foo/commondir &&
+	(
+		cd work &&
+		GIT_DIR=../gitfile git rev-parse --git-common-dir >actual &&
+		test-path-utils real_path "$TRASH_DIRECTORY/repo.git" >expect &&
+		test_cmp expect actual
+	)
+'
+
+test_expect_success 'GIT_DIR set (2)' '
+	echo "gitdir: repo.git/repos/foo" >gitfile &&
+	echo "$(pwd)/repo.git" >repo.git/repos/foo/commondir &&
+	(
+		cd work &&
+		GIT_DIR=../gitfile git rev-parse --git-common-dir >actual &&
+		test-path-utils real_path "$TRASH_DIRECTORY/repo.git" >expect &&
+		test_cmp expect actual
+	)
+'
+
+test_expect_success 'Auto discovery' '
+	echo "gitdir: repo.git/repos/foo" >.git &&
+	echo ../.. >repo.git/repos/foo/commondir &&
+	(
+		cd work &&
+		git rev-parse --git-common-dir >actual &&
+		test-path-utils real_path "$TRASH_DIRECTORY/repo.git" >expect &&
+		test_cmp expect actual &&
+		echo haha >data1 &&
+		git add data1 &&
+		git ls-files --full-name :/ | grep data1 >actual &&
+		echo work/data1 >expect &&
+		test_cmp expect actual
+	)
+'
+
+test_expect_success '$GIT_DIR/common overrides core.worktree' '
+	mkdir elsewhere &&
+	git --git-dir=repo.git config core.worktree "$TRASH_DIRECTORY/elsewhere" &&
+	echo "gitdir: repo.git/repos/foo" >.git &&
+	echo ../.. >repo.git/repos/foo/commondir &&
+	(
+		cd work &&
+		git rev-parse --git-common-dir >actual &&
+		test-path-utils real_path "$TRASH_DIRECTORY/repo.git" >expect &&
+		test_cmp expect actual &&
+		echo haha >data2 &&
+		git add data2 &&
+		git ls-files --full-name :/ | grep data2 >actual &&
+		echo work/data2 >expect &&
+		test_cmp expect actual
+	)
+'
+
+test_expect_success '$GIT_WORK_TREE overrides $GIT_DIR/common' '
+	echo "gitdir: repo.git/repos/foo" >.git &&
+	echo ../.. >repo.git/repos/foo/commondir &&
+	(
+		cd work &&
+		echo haha >data3 &&
+		git --git-dir=../.git --work-tree=. add data3 &&
+		git ls-files --full-name -- :/ | grep data3 >actual &&
+		echo data3 >expect &&
+		test_cmp expect actual
+	)
+'
+
 test_done
diff --git a/t/t1510-repo-setup.sh b/t/t1510-repo-setup.sh
index e1b2a99..33c1a58 100755
--- a/t/t1510-repo-setup.sh
+++ b/t/t1510-repo-setup.sh
@@ -106,6 +106,7 @@ setup_env () {
 expect () {
 	cat >"$1/expected" <<-EOF
 	setup: git_dir: $2
+	setup: git_common_dir: $2
 	setup: worktree: $3
 	setup: cwd: $4
 	setup: prefix: $5
diff --git a/trace.c b/trace.c
index 4778608..bc3f53d 100644
--- a/trace.c
+++ b/trace.c
@@ -312,6 +312,7 @@ void trace_repo_setup(const char *prefix)
 		prefix = "(null)";
 
 	trace_printf_key(&key, "setup: git_dir: %s\n", quote_crnl(get_git_dir()));
+	trace_printf_key(&key, "setup: git_common_dir: %s\n", quote_crnl(get_git_common_dir()));
 	trace_printf_key(&key, "setup: worktree: %s\n", quote_crnl(git_work_tree));
 	trace_printf_key(&key, "setup: cwd: %s\n", quote_crnl(cwd));
 	trace_printf_key(&key, "setup: prefix: %s\n", quote_crnl(prefix));
-- 
2.1.0.rc0.78.gc0d8480

[PATCH 20/34] wrapper.c: wrapper to open a file, fprintf then close

[Nguyễn Thái Ngọc Duy]

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
---
 cache.h   |  2 ++
 wrapper.c | 31 +++++++++++++++++++++++++++++++
 2 files changed, 33 insertions(+)

diff --git a/cache.h b/cache.h
index 9dc6ae0..f8e75a1 100644
--- a/cache.h
+++ b/cache.h
@@ -1499,6 +1499,8 @@ static inline ssize_t write_str_in_full(int fd, const char *str)
 {
 	return write_in_full(fd, str, strlen(str));
 }
+__attribute__((format (printf,3,4)))
+extern int write_file(const char *path, int fatal, const char *fmt, ...);
 
 /* pager.c */
 extern void setup_pager(void);
diff --git a/wrapper.c b/wrapper.c
index 007ec0d..a2dff8e 100644
--- a/wrapper.c
+++ b/wrapper.c
@@ -550,3 +550,34 @@ char *xgetcwd(void)
 		die_errno(_("unable to get current working directory"));
 	return strbuf_detach(&sb, NULL);
 }
+
+int write_file(const char *path, int fatal, const char *fmt, ...)
+{
+	struct strbuf sb = STRBUF_INIT;
+	va_list params;
+	int fd = open(path, O_RDWR | O_CREAT | O_TRUNC, 0666);
+	if (fd < 0) {
+		if (fatal)
+			die_errno(_("could not open %s for writing"), path);
+		return -1;
+	}
+	va_start(params, fmt);
+	strbuf_vaddf(&sb, fmt, params);
+	va_end(params);
+	if (write_in_full(fd, sb.buf, sb.len) != sb.len) {
+		int err = errno;
+		close(fd);
+		strbuf_release(&sb);
+		errno = err;
+		if (fatal)
+			die_errno(_("could not write to %s"), path);
+		return -1;
+	}
+	strbuf_release(&sb);
+	if (close(fd)) {
+		if (fatal)
+			die_errno(_("could not close %s"), path);
+		return -1;
+	}
+	return 0;
+}
-- 
2.1.0.rc0.78.gc0d8480

[PATCH 21/34] use new wrapper write_file() for simple file writing

[Nguyễn Thái Ngọc Duy]

This fixes common problems in these code about error handling,
forgetting to close the file handle after fprintf() fails, or not
printing out the error string..

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
---
 builtin/branch.c  |  4 +---
 builtin/init-db.c |  7 +------
 daemon.c          | 11 +----------
 submodule.c       |  9 ++-------
 transport.c       |  8 +++-----
 5 files changed, 8 insertions(+), 31 deletions(-)

diff --git a/builtin/branch.c b/builtin/branch.c
index 3b79c50..1a475d8 100644
--- a/builtin/branch.c
+++ b/builtin/branch.c
@@ -764,7 +764,6 @@ static const char edit_description[] = "BRANCH_DESCRIPTION";
 
 static int edit_branch_description(const char *branch_name)
 {
-	FILE *fp;
 	int status;
 	struct strbuf buf = STRBUF_INIT;
 	struct strbuf name = STRBUF_INIT;
@@ -777,8 +776,7 @@ static int edit_branch_description(const char *branch_name)
 		    "  %s\n"
 		    "Lines starting with '%c' will be stripped.\n",
 		    branch_name, comment_line_char);
-	fp = fopen(git_path(edit_description), "w");
-	if ((fwrite(buf.buf, 1, buf.len, fp) < buf.len) || fclose(fp)) {
+	if (write_file(git_path(edit_description), 0, "%s", buf.buf)) {
 		strbuf_release(&buf);
 		return error(_("could not write branch description template: %s"),
 			     strerror(errno));
diff --git a/builtin/init-db.c b/builtin/init-db.c
index 587a505..6b7fa5f 100644
--- a/builtin/init-db.c
+++ b/builtin/init-db.c
@@ -342,7 +342,6 @@ int set_git_dir_init(const char *git_dir, const char *real_git_dir,
 static void separate_git_dir(const char *git_dir)
 {
 	struct stat st;
-	FILE *fp;
 
 	if (!stat(git_link, &st)) {
 		const char *src;
@@ -358,11 +357,7 @@ static void separate_git_dir(const char *git_dir)
 			die_errno(_("unable to move %s to %s"), src, git_dir);
 	}
 
-	fp = fopen(git_link, "w");
-	if (!fp)
-		die(_("Could not create git link %s"), git_link);
-	fprintf(fp, "gitdir: %s\n", git_dir);
-	fclose(fp);
+	write_file(git_link, 1, "gitdir: %s\n", git_dir);
 }
 
 int init_db(const char *template_dir, unsigned int flags)
diff --git a/daemon.c b/daemon.c
index 54a03bd..60bbab6 100644
--- a/daemon.c
+++ b/daemon.c
@@ -1070,15 +1070,6 @@ static struct credentials *prepare_credentials(const char *user_name,
 }
 #endif
 
-static void store_pid(const char *path)
-{
-	FILE *f = fopen(path, "w");
-	if (!f)
-		die_errno("cannot open pid file '%s'", path);
-	if (fprintf(f, "%"PRIuMAX"\n", (uintmax_t) getpid()) < 0 || fclose(f) != 0)
-		die_errno("failed to write pid file '%s'", path);
-}
-
 static int serve(struct string_list *listen_addr, int listen_port,
     struct credentials *cred)
 {
@@ -1289,7 +1280,7 @@ int main(int argc, char **argv)
 		sanitize_stdfds();
 
 	if (pid_file)
-		store_pid(pid_file);
+		write_file(pid_file, 1, "%"PRIuMAX"\n", (uintmax_t) getpid());
 
 	/* prepare argv for serving-processes */
 	cld_argv = xmalloc(sizeof (char *) * (argc + 2));
diff --git a/submodule.c b/submodule.c
index 0690dc5..34094f5 100644
--- a/submodule.c
+++ b/submodule.c
@@ -1102,16 +1102,11 @@ void connect_work_tree_and_git_dir(const char *work_tree, const char *git_dir)
 	struct strbuf file_name = STRBUF_INIT;
 	struct strbuf rel_path = STRBUF_INIT;
 	const char *real_work_tree = xstrdup(real_path(work_tree));
-	FILE *fp;
 
 	/* Update gitfile */
 	strbuf_addf(&file_name, "%s/.git", work_tree);
-	fp = fopen(file_name.buf, "w");
-	if (!fp)
-		die(_("Could not create git link %s"), file_name.buf);
-	fprintf(fp, "gitdir: %s\n", relative_path(git_dir, real_work_tree,
-						  &rel_path));
-	fclose(fp);
+	write_file(file_name.buf, 1, "gitdir: %s\n",
+		   relative_path(git_dir, real_work_tree, &rel_path));
 
 	/* Update core.worktree setting */
 	strbuf_reset(&file_name);
diff --git a/transport.c b/transport.c
index 70d38e4..051b7ac 100644
--- a/transport.c
+++ b/transport.c
@@ -283,7 +283,6 @@ static int write_one_ref(const char *name, const unsigned char *sha1,
 {
 	struct strbuf *buf = data;
 	int len = buf->len;
-	FILE *f;
 
 	/* when called via for_each_ref(), flags is non-zero */
 	if (flags && !starts_with(name, "refs/heads/") &&
@@ -292,10 +291,9 @@ static int write_one_ref(const char *name, const unsigned char *sha1,
 
 	strbuf_addstr(buf, name);
 	if (safe_create_leading_directories(buf->buf) ||
-			!(f = fopen(buf->buf, "w")) ||
-			fprintf(f, "%s\n", sha1_to_hex(sha1)) < 0 ||
-			fclose(f))
-		return error("problems writing temporary file %s", buf->buf);
+	    write_file(buf->buf, 0, "%s\n", sha1_to_hex(sha1)))
+		return error("problems writing temporary file %s: %s",
+			     buf->buf, strerror(errno));
 	strbuf_setlen(buf, len);
 	return 0;
 }
-- 
2.1.0.rc0.78.gc0d8480

[PATCH 22/34] checkout: support checking out into a new working directory

[Nguyễn Thái Ngọc Duy]

"git checkout --to" sets up a new working directory with a .git file
pointing to $GIT_DIR/worktrees/<id>. It then executes "git checkout"
again on the new worktree with the same arguments except "--to" is
taken out. The second checkout execution, which is not contaminated
with any info from the current repository, will actually check out and
everything that normal "git checkout" does.

Helped-by: Marc Branchaud <marcnarc@xiplink.com>
Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
---
 Documentation/git-checkout.txt         | 46 ++++++++++++++++
 Documentation/git.txt                  |  3 +-
 Documentation/gitrepository-layout.txt |  7 +++
 builtin/checkout.c                     | 95 +++++++++++++++++++++++++++++++++-
 path.c                                 |  2 +-
 t/t2025-checkout-to.sh (new +x)        | 63 ++++++++++++++++++++++
 6 files changed, 212 insertions(+), 4 deletions(-)
 create mode 100755 t/t2025-checkout-to.sh

diff --git a/Documentation/git-checkout.txt b/Documentation/git-checkout.txt
index 33ad2ad..c101575 100644
--- a/Documentation/git-checkout.txt
+++ b/Documentation/git-checkout.txt
@@ -225,6 +225,13 @@ This means that you can use `git checkout -p` to selectively discard
 edits from your current working tree. See the ``Interactive Mode''
 section of linkgit:git-add[1] to learn how to operate the `--patch` mode.
 
+--to=<path>::
+	Check out a branch in a separate working directory at
+	`<path>`. A new working directory is linked to the current
+	repository, sharing everything except working directory
+	specific files such as HEAD, index... See "MULTIPLE WORKING
+	TREES" section for more information.
+
 <branch>::
 	Branch to checkout; if it refers to a branch (i.e., a name that,
 	when prepended with "refs/heads/", is a valid ref), then that
@@ -388,6 +395,45 @@ $ git reflog -2 HEAD # or
 $ git log -g -2 HEAD
 ------------
 
+MULTIPLE WORKING TREES
+----------------------
+
+A git repository can support multiple working trees, allowing you to check
+out more than one branch at a time.  With `git checkout --to` a new working
+tree is associated with the repository.  This new working tree is called a
+"linked working tree" as opposed to the "main working tree" prepared by "git
+init" or "git clone".  A repository has one main working tree (if it's not a
+bare repository) and zero or more linked working trees.
+
+Each linked working tree has a private sub-directory in the repository's
+$GIT_DIR/worktrees directory.  The private sub-directory's name is usually
+the base name of the linked working tree's path, possibly appended with a
+number to make it unique.  For example, when `$GIT_DIR=/path/main/.git` the
+command `git checkout --to /path/other/test-next next` creates the linked
+working tree in `/path/other/test-next` and also creates a
+`$GIT_DIR/worktrees/test-next` directory (or `$GIT_DIR/worktrees/test-next1`
+if `test-next` is already taken).
+
+Within a linked working tree, $GIT_DIR is set to point to this private
+directory (e.g. `/path/main/.git/worktrees/test-next` in the example) and
+$GIT_COMMON_DIR is set to point back to the main working tree's $GIT_DIR
+(e.g. `/path/main/.git`). These settings are made in a `.git` file located at
+the top directory of the linked working tree.
+
+Path resolution via `git rev-parse --git-path` uses either
+$GIT_DIR or $GIT_COMMON_DIR depending on the path. For example, in the
+linked working tree `git rev-parse --git-path HEAD` returns
+`/path/main/.git/worktrees/test-next/HEAD` (not
+`/path/other/test-next/.git/HEAD` or `/path/main/.git/HEAD`) while `git
+rev-parse --git-path refs/heads/master` uses
+$GIT_COMMON_DIR and returns `/path/main/.git/refs/heads/master`,
+since refs are shared across all working trees.
+
+See linkgit:gitrepository-layout[5] for more information. The rule of
+thumb is do not make any assumption about whether a path belongs to
+$GIT_DIR or $GIT_COMMON_DIR when you need to directly access something
+inside $GIT_DIR. Use `git rev-parse --git-path` to get the final path.
+
 EXAMPLES
 --------
 
diff --git a/Documentation/git.txt b/Documentation/git.txt
index 96354af..0c2dcfa 100644
--- a/Documentation/git.txt
+++ b/Documentation/git.txt
@@ -813,7 +813,8 @@ Git so take care if using Cogito etc.
 	If this variable is set to a path, non-worktree files that are
 	normally in $GIT_DIR will be taken from this path
 	instead. Worktree-specific files such as HEAD or index are
-	taken from $GIT_DIR. See linkgit:gitrepository-layout[5] for
+	taken from $GIT_DIR. See linkgit:gitrepository-layout[5] and
+	the section 'MULTIPLE CHECKOUT MODE' in linkgit:checkout[1]
 	details. This variable has lower precedence than other path
 	variables such as GIT_INDEX_FILE, GIT_OBJECT_DIRECTORY...
 
diff --git a/Documentation/gitrepository-layout.txt b/Documentation/gitrepository-layout.txt
index 2dc5667..8228450 100644
--- a/Documentation/gitrepository-layout.txt
+++ b/Documentation/gitrepository-layout.txt
@@ -252,6 +252,13 @@ modules::
 	directory is ignored if $GIT_COMMON_DIR is set and
 	"$GIT_COMMON_DIR/modules" will be used instead.
 
+worktrees::
+	Contains worktree specific information of linked
+	checkouts. Each subdirectory contains the worktree-related
+	part of a linked checkout. This directory is ignored if
+	$GIT_COMMON_DIR is set and "$GIT_COMMON_DIR/worktrees" will be
+	used instead.
+
 SEE ALSO
 --------
 linkgit:git-init[1],
diff --git a/builtin/checkout.c b/builtin/checkout.c
index 195aca7..797e14d 100644
--- a/builtin/checkout.c
+++ b/builtin/checkout.c
@@ -48,6 +48,10 @@ struct checkout_opts {
 	const char *prefix;
 	struct pathspec pathspec;
 	struct tree *source_tree;
+
+	const char *new_worktree;
+	const char **saved_argv;
+	int new_worktree_mode;
 };
 
 static int post_checkout_hook(struct commit *old, struct commit *new,
@@ -249,6 +253,9 @@ static int checkout_paths(const struct checkout_opts *opts,
 		die(_("Cannot update paths and switch to branch '%s' at the same time."),
 		    opts->new_branch);
 
+	if (opts->new_worktree)
+		die(_("'%s' cannot be used with updating paths"), "--to");
+
 	if (opts->patch_mode)
 		return run_add_interactive(revision, "--patch=checkout",
 					   &opts->pathspec);
@@ -484,7 +491,7 @@ static int merge_working_tree(const struct checkout_opts *opts,
 			topts.dir->flags |= DIR_SHOW_IGNORED;
 			setup_standard_excludes(topts.dir);
 		}
-		tree = parse_tree_indirect(old->commit ?
+		tree = parse_tree_indirect(old->commit && !opts->new_worktree_mode ?
 					   old->commit->object.sha1 :
 					   EMPTY_TREE_SHA1_BIN);
 		init_tree_desc(&trees[0], tree->buffer, tree->size);
@@ -800,7 +807,8 @@ static int switch_branches(const struct checkout_opts *opts,
 		return ret;
 	}
 
-	if (!opts->quiet && !old.path && old.commit && new->commit != old.commit)
+	if (!opts->quiet && !old.path && old.commit &&
+	    new->commit != old.commit && !opts->new_worktree_mode)
 		orphaned_commit_warning(old.commit, new->commit);
 
 	update_refs_for_switch(opts, &old, new);
@@ -810,6 +818,76 @@ static int switch_branches(const struct checkout_opts *opts,
 	return ret || writeout_error;
 }
 
+static int prepare_linked_checkout(const struct checkout_opts *opts,
+				   struct branch_info *new)
+{
+	struct strbuf sb_git = STRBUF_INIT, sb_repo = STRBUF_INIT;
+	struct strbuf sb = STRBUF_INIT;
+	const char *path = opts->new_worktree, *name;
+	struct stat st;
+	struct child_process cp;
+	int counter = 0, len;
+
+	if (!new->commit)
+		die(_("no branch specified"));
+	if (file_exists(path))
+		die(_("'%s' already exists"), path);
+
+	len = strlen(path);
+	while (len && is_dir_sep(path[len - 1]))
+		len--;
+
+	for (name = path + len - 1; name > path; name--)
+		if (is_dir_sep(*name)) {
+			name++;
+			break;
+		}
+	strbuf_addstr(&sb_repo,
+		      git_path("worktrees/%.*s", (int)(path + len - name), name));
+	len = sb_repo.len;
+	if (safe_create_leading_directories_const(sb_repo.buf))
+		die_errno(_("could not create leading directories of '%s'"),
+			  sb_repo.buf);
+	while (!stat(sb_repo.buf, &st)) {
+		counter++;
+		strbuf_setlen(&sb_repo, len);
+		strbuf_addf(&sb_repo, "%d", counter);
+	}
+	name = strrchr(sb_repo.buf, '/') + 1;
+	if (mkdir(sb_repo.buf, 0777))
+		die_errno(_("could not create directory of '%s'"), sb_repo.buf);
+
+	strbuf_addf(&sb_git, "%s/.git", path);
+	if (safe_create_leading_directories_const(sb_git.buf))
+		die_errno(_("could not create leading directories of '%s'"),
+			  sb_git.buf);
+
+	write_file(sb_git.buf, 1, "gitdir: %s/worktrees/%s\n",
+		   real_path(get_git_common_dir()), name);
+	/*
+	 * This is to keep resolve_ref() happy. We need a valid HEAD
+	 * or is_git_directory() will reject the directory. Any valid
+	 * value would do because this value will be ignored and
+	 * replaced at the next (real) checkout.
+	 */
+	strbuf_addf(&sb, "%s/HEAD", sb_repo.buf);
+	write_file(sb.buf, 1, "%s\n", sha1_to_hex(new->commit->object.sha1));
+	strbuf_reset(&sb);
+	strbuf_addf(&sb, "%s/commondir", sb_repo.buf);
+	write_file(sb.buf, 1, "../..\n");
+
+	if (!opts->quiet)
+		fprintf_ln(stderr, _("Enter %s (identifier %s)"), path, name);
+
+	setenv("GIT_CHECKOUT_NEW_WORKTREE", "1", 1);
+	setenv(GIT_DIR_ENVIRONMENT, sb_git.buf, 1);
+	setenv(GIT_WORK_TREE_ENVIRONMENT, path, 1);
+	memset(&cp, 0, sizeof(cp));
+	cp.git_cmd = 1;
+	cp.argv = opts->saved_argv;
+	return run_command(&cp);
+}
+
 static int git_checkout_config(const char *var, const char *value, void *cb)
 {
 	if (!strcmp(var, "diff.ignoresubmodules")) {
@@ -1071,6 +1149,9 @@ static int checkout_branch(struct checkout_opts *opts,
 		die(_("Cannot switch branch to a non-commit '%s'"),
 		    new->name);
 
+	if (opts->new_worktree)
+		return prepare_linked_checkout(opts, new);
+
 	if (!new->commit && opts->new_branch) {
 		unsigned char rev[20];
 		int flag;
@@ -1113,6 +1194,8 @@ int cmd_checkout(int argc, const char **argv, const char *prefix)
 			 N_("do not limit pathspecs to sparse entries only")),
 		OPT_HIDDEN_BOOL(0, "guess", &dwim_new_local_branch,
 				N_("second guess 'git checkout no-such-branch'")),
+		OPT_FILENAME(0, "to", &opts.new_worktree,
+			   N_("check a branch out in a separate working directory")),
 		OPT_END(),
 	};
 
@@ -1121,6 +1204,9 @@ int cmd_checkout(int argc, const char **argv, const char *prefix)
 	opts.overwrite_ignore = 1;
 	opts.prefix = prefix;
 
+	opts.saved_argv = xmalloc(sizeof(const char *) * (argc + 2));
+	memcpy(opts.saved_argv, argv, sizeof(const char *) * (argc + 1));
+
 	gitmodules_config();
 	git_config(git_checkout_config, &opts);
 
@@ -1129,6 +1215,11 @@ int cmd_checkout(int argc, const char **argv, const char *prefix)
 	argc = parse_options(argc, argv, prefix, options, checkout_usage,
 			     PARSE_OPT_KEEP_DASHDASH);
 
+	/* recursive execution from checkout_new_worktree() */
+	opts.new_worktree_mode = getenv("GIT_CHECKOUT_NEW_WORKTREE") != NULL;
+	if (opts.new_worktree_mode)
+		opts.new_worktree = NULL;
+
 	if (conflict_style) {
 		opts.merge = 1; /* implied */
 		git_xmerge_config("merge.conflictstyle", conflict_style, NULL);
diff --git a/path.c b/path.c
index 94db501..72eca6d 100644
--- a/path.c
+++ b/path.c
@@ -92,7 +92,7 @@ static void replace_dir(struct strbuf *buf, int len, const char *newdir)
 
 static const char *common_list[] = {
 	"/branches", "/hooks", "/info", "/logs", "/lost-found", "/modules",
-	"/objects", "/refs", "/remotes", "/rr-cache", "/svn",
+	"/objects", "/refs", "/remotes", "/worktrees", "/rr-cache", "/svn",
 	"config", "gc.pid", "packed-refs", "shallow",
 	NULL
 };
diff --git a/t/t2025-checkout-to.sh b/t/t2025-checkout-to.sh
new file mode 100755
index 0000000..4963415
--- /dev/null
+++ b/t/t2025-checkout-to.sh
@@ -0,0 +1,63 @@
+#!/bin/sh
+
+test_description='test git checkout --to'
+
+. ./test-lib.sh
+
+test_expect_success 'setup' '
+	test_commit init
+'
+
+test_expect_success 'checkout --to not updating paths' '
+	test_must_fail git checkout --to -- init.t
+'
+
+test_expect_success 'checkout --to an existing worktree' '
+	mkdir existing &&
+	test_must_fail git checkout --detach --to existing master
+'
+
+test_expect_success 'checkout --to a new worktree' '
+	git checkout --to here master &&
+	(
+		cd here &&
+		test_cmp ../init.t init.t &&
+		git symbolic-ref HEAD >actual &&
+		echo refs/heads/master >expect &&
+		test_cmp expect actual &&
+		git fsck
+	)
+'
+
+test_expect_success 'checkout --to a new worktree from a subdir' '
+	(
+		mkdir sub &&
+		cd sub &&
+		git checkout --detach --to here master &&
+		cd here &&
+		test_cmp ../../init.t init.t
+	)
+'
+
+test_expect_success 'checkout --to from a linked checkout' '
+	(
+		cd here &&
+		git checkout --to nested-here master &&
+		cd nested-here &&
+		git fsck
+	)
+'
+
+test_expect_success 'checkout --to a new worktree creating new branch' '
+	git checkout --to there -b newmaster master &&
+	(
+		cd there &&
+		test_cmp ../init.t init.t &&
+		git symbolic-ref HEAD >actual &&
+		echo refs/heads/newmaster >expect &&
+		test_cmp expect actual &&
+		git fsck
+	)
+'
+
+test_done
-- 
2.1.0.rc0.78.gc0d8480

[PATCH 23/34] prune: strategies for linked checkouts

[Nguyễn Thái Ngọc Duy]

(alias R=$GIT_COMMON_DIR/worktrees/<id>)

 - linked checkouts are supposed to keep its location in $R/gitdir up
   to date. The use case is auto fixup after a manual checkout move.

 - linked checkouts are supposed to update mtime of $R/gitdir. If
   $R/gitdir's mtime is older than a limit, and it points to nowhere,
   worktrees/<id> is to be pruned.

 - If $R/locked exists, worktrees/<id> is not supposed to be pruned. If
   $R/locked exists and $R/gitdir's mtime is older than a really long
   limit, warn about old unused repo.

 - "git checkout --to" is supposed to make a hard link named $R/link
   pointing to the .git file on supported file systems to help detect
   the user manually deleting the checkout. If $R/link exists and its
   link count is greated than 1, the repo is kept.

Helped-by: Marc Branchaud <marcnarc@xiplink.com>
Helped-by: Eric Sunshine <sunshine@sunshineco.com>
Helped-by: Johannes Sixt <j6t@kdbg.org>
Signed-off-by: Marc Branchaud <marcnarc@xiplink.com>
Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
---
 Documentation/git-checkout.txt             | 20 +++++++
 Documentation/git-prune.txt                |  3 +
 Documentation/gitrepository-layout.txt     | 19 ++++++
 builtin/checkout.c                         | 19 +++++-
 builtin/prune.c                            | 95 ++++++++++++++++++++++++++++++
 setup.c                                    | 13 ++++
 t/t2026-prune-linked-checkouts.sh (new +x) | 84 ++++++++++++++++++++++++++
 7 files changed, 251 insertions(+), 2 deletions(-)
 create mode 100755 t/t2026-prune-linked-checkouts.sh

diff --git a/Documentation/git-checkout.txt b/Documentation/git-checkout.txt
index c101575..35675da 100644
--- a/Documentation/git-checkout.txt
+++ b/Documentation/git-checkout.txt
@@ -434,6 +434,26 @@ thumb is do not make any assumption about whether a path belongs to
 $GIT_DIR or $GIT_COMMON_DIR when you need to directly access something
 inside $GIT_DIR. Use `git rev-parse --git-path` to get the final path.
 
+When you are done with a linked working tree you can simply delete it.
+You can clean up any stale $GIT_DIR/worktrees entries via `git prune
+--worktrees` in the main or any linked working tree.
+
+If you move a linked working directory to another file system, or
+within a file system that does not support hard links, you need to run
+at least one git command inside the linked working directory
+(e.g. `git status`) in order to update its entry in $GIT_DIR/worktrees
+so that it does not get automatically removed.
+
+To prevent `git prune --worktrees` from deleting a $GIT_DIR/worktrees
+entry (which can be useful in some situations, such as when the
+entry's working tree is stored on a portable device), add a file named
+'locked' to the entry's directory. The file contains the reason in
+plain text. For example, if a linked working tree's `.git` file points
+to `/path/main/.git/worktrees/test-next` then a file named
+`/path/main/.git/worktrees/test-next/locked` will prevent the
+`test-next` entry from being pruned.  See
+linkgit:gitrepository-layout[5] for details.
+
 EXAMPLES
 --------
 
diff --git a/Documentation/git-prune.txt b/Documentation/git-prune.txt
index 7a493c8..1cf3bed 100644
--- a/Documentation/git-prune.txt
+++ b/Documentation/git-prune.txt
@@ -48,6 +48,9 @@ OPTIONS
 --expire <time>::
 	Only expire loose objects older than <time>.
 
+--worktrees::
+	Prune dead working tree information in $GIT_DIR/worktrees.
+
 <head>...::
 	In addition to objects
 	reachable from any of our references, keep objects
diff --git a/Documentation/gitrepository-layout.txt b/Documentation/gitrepository-layout.txt
index 8228450..2b30a92 100644
--- a/Documentation/gitrepository-layout.txt
+++ b/Documentation/gitrepository-layout.txt
@@ -259,6 +259,25 @@ worktrees::
 	$GIT_COMMON_DIR is set and "$GIT_COMMON_DIR/worktrees" will be
 	used instead.
 
+worktrees/<id>/gitdir::
+	A text file containing the absolute path back to the .git file
+	that points to here. This is used to check if the linked
+	repository has been manually removed and there is no need to
+	keep this directory any more. mtime of this file should be
+	updated every time the linked repository is accessed.
+
+worktrees/<id>/locked::
+	If this file exists, the linked repository may be on a
+	portable device and not available. It does not mean that the
+	linked repository is gone and `worktrees/<id>` could be
+	removed. The file's content contains a reason string on why
+	the repository is locked.
+
+worktrees/<id>/link::
+	If this file exists, it is a hard link to the linked .git
+	file. It is used to detect if the linked repository is
+	manually removed.
+
 SEE ALSO
 --------
 linkgit:git-init[1],
diff --git a/builtin/checkout.c b/builtin/checkout.c
index 797e14d..645135a 100644
--- a/builtin/checkout.c
+++ b/builtin/checkout.c
@@ -826,7 +826,7 @@ static int prepare_linked_checkout(const struct checkout_opts *opts,
 	const char *path = opts->new_worktree, *name;
 	struct stat st;
 	struct child_process cp;
-	int counter = 0, len;
+	int counter = 0, len, ret;
 
 	if (!new->commit)
 		die(_("no branch specified"));
@@ -857,11 +857,21 @@ static int prepare_linked_checkout(const struct checkout_opts *opts,
 	if (mkdir(sb_repo.buf, 0777))
 		die_errno(_("could not create directory of '%s'"), sb_repo.buf);
 
+	/*
+	 * lock the incomplete repo so prune won't delete it, unlock
+	 * after the preparation is over.
+	 */
+	strbuf_addf(&sb, "%s/locked", sb_repo.buf);
+	write_file(sb.buf, 1, "initializing\n");
+
 	strbuf_addf(&sb_git, "%s/.git", path);
 	if (safe_create_leading_directories_const(sb_git.buf))
 		die_errno(_("could not create leading directories of '%s'"),
 			  sb_git.buf);
 
+	strbuf_reset(&sb);
+	strbuf_addf(&sb, "%s/gitdir", sb_repo.buf);
+	write_file(sb.buf, 1, "%s\n", real_path(sb_git.buf));
 	write_file(sb_git.buf, 1, "gitdir: %s/worktrees/%s\n",
 		   real_path(get_git_common_dir()), name);
 	/*
@@ -870,6 +880,7 @@ static int prepare_linked_checkout(const struct checkout_opts *opts,
 	 * value would do because this value will be ignored and
 	 * replaced at the next (real) checkout.
 	 */
+	strbuf_reset(&sb);
 	strbuf_addf(&sb, "%s/HEAD", sb_repo.buf);
 	write_file(sb.buf, 1, "%s\n", sha1_to_hex(new->commit->object.sha1));
 	strbuf_reset(&sb);
@@ -885,7 +896,11 @@ static int prepare_linked_checkout(const struct checkout_opts *opts,
 	memset(&cp, 0, sizeof(cp));
 	cp.git_cmd = 1;
 	cp.argv = opts->saved_argv;
-	return run_command(&cp);
+	ret = run_command(&cp);
+	strbuf_reset(&sb);
+	strbuf_addf(&sb, "%s/locked", sb_repo.buf);
+	unlink_or_warn(sb.buf);
+	return ret;
 }
 
 static int git_checkout_config(const char *var, const char *value, void *cb)
diff --git a/builtin/prune.c b/builtin/prune.c
index 04d3b12..f08670a 100644
--- a/builtin/prune.c
+++ b/builtin/prune.c
@@ -76,6 +76,91 @@ static int prune_subdir(int nr, const char *path, void *data)
 	return 0;
 }
 
+static int prune_worktree(const char *id, struct strbuf *reason)
+{
+	struct stat st;
+	char *path;
+	int fd, len;
+
+	if (!is_directory(git_path("worktrees/%s", id))) {
+		strbuf_addf(reason, _("Removing worktrees/%s: not a valid directory"), id);
+		return 1;
+	}
+	if (file_exists(git_path("worktrees/%s/locked", id)))
+		return 0;
+	if (stat(git_path("worktrees/%s/gitdir", id), &st)) {
+		strbuf_addf(reason, _("Removing worktrees/%s: gitdir file does not exist"), id);
+		return 1;
+	}
+	fd = open(git_path("worktrees/%s/gitdir", id), O_RDONLY);
+	if (fd < 0) {
+		strbuf_addf(reason, _("Removing worktrees/%s: unable to read gitdir file (%s)"),
+			    id, strerror(errno));
+		return 1;
+	}
+	len = st.st_size;
+	path = xmalloc(len + 1);
+	read_in_full(fd, path, len);
+	close(fd);
+	while (len && (path[len - 1] == '\n' || path[len - 1] == '\r'))
+		len--;
+	if (!len) {
+		strbuf_addf(reason, _("Removing worktrees/%s: invalid gitdir file"), id);
+		free(path);
+		return 1;
+	}
+	path[len] = '\0';
+	if (!file_exists(path)) {
+		struct stat st_link;
+		free(path);
+		/*
+		 * the repo is moved manually and has not been
+		 * accessed since?
+		 */
+		if (!stat(git_path("worktrees/%s/link", id), &st_link) &&
+		    st_link.st_nlink > 1)
+			return 0;
+		strbuf_addf(reason, _("Removing worktrees/%s: gitdir file points to non-existent location"), id);
+		return 1;
+	}
+	free(path);
+	return st.st_mtime <= expire;
+}
+
+static void prune_worktrees(void)
+{
+	struct strbuf reason = STRBUF_INIT;
+	struct strbuf path = STRBUF_INIT;
+	DIR *dir = opendir(git_path("worktrees"));
+	struct dirent *d;
+	int ret;
+	if (!dir)
+		return;
+	while ((d = readdir(dir)) != NULL) {
+		if (!strcmp(d->d_name, ".") || !strcmp(d->d_name, ".."))
+			continue;
+		strbuf_reset(&reason);
+		if (!prune_worktree(d->d_name, &reason))
+			continue;
+		if (show_only || verbose)
+			printf("%s\n", reason.buf);
+		if (show_only)
+			continue;
+		strbuf_reset(&path);
+		strbuf_addstr(&path, git_path("worktrees/%s", d->d_name));
+		ret = remove_dir_recursively(&path, 0);
+		if (ret < 0 && errno == ENOTDIR)
+			ret = unlink(path.buf);
+		if (ret)
+			error(_("failed to remove: %s"), strerror(errno));
+	}
+	closedir(dir);
+	if (!show_only)
+		rmdir(git_path("worktrees"));
+	strbuf_release(&reason);
+	strbuf_release(&path);
+}
+
 /*
  * Write errors (particularly out of space) can result in
  * failed temporary packs (and more rarely indexes and other
@@ -102,10 +187,12 @@ int cmd_prune(int argc, const char **argv, const char *prefix)
 {
 	struct rev_info revs;
 	struct progress *progress = NULL;
+	int do_prune_worktrees = 0;
 	const struct option options[] = {
 		OPT__DRY_RUN(&show_only, N_("do not remove, show only")),
 		OPT__VERBOSE(&verbose, N_("report pruned objects")),
 		OPT_BOOL(0, "progress", &show_progress, N_("show progress")),
+		OPT_BOOL(0, "worktrees", &do_prune_worktrees, N_("prune .git/worktrees")),
 		OPT_EXPIRY_DATE(0, "expire", &expire,
 				N_("expire objects older than <time>")),
 		OPT_END()
@@ -118,6 +205,14 @@ int cmd_prune(int argc, const char **argv, const char *prefix)
 	init_revisions(&revs, prefix);
 
 	argc = parse_options(argc, argv, prefix, options, prune_usage, 0);
+
+	if (do_prune_worktrees) {
+		if (argc)
+			die(_("--worktrees does not take extra arguments"));
+		prune_worktrees();
+		return 0;
+	}
+
 	while (argc--) {
 		unsigned char sha1[20];
 		const char *name = *argv++;
diff --git a/setup.c b/setup.c
index b99bdd3..fb61860 100644
--- a/setup.c
+++ b/setup.c
@@ -390,6 +390,17 @@ static int check_repository_format_gently(const char *gitdir, int *nongit_ok)
 	return ret;
 }
 
+static void update_linked_gitdir(const char *gitfile, const char *gitdir)
+{
+	struct strbuf path = STRBUF_INIT;
+	struct stat st;
+
+	strbuf_addf(&path, "%s/gitfile", gitdir);
+	if (stat(path.buf, &st) || st.st_mtime + 24 * 3600 < time(NULL))
+		write_file(path.buf, 0, "%s\n", gitfile);
+	strbuf_release(&path);
+}
+
 /*
  * Try to read the location of the git directory from the .git file,
  * return path to git directory if found.
@@ -438,6 +449,8 @@ const char *read_gitfile(const char *path)
 
 	if (!is_git_directory(dir))
 		die("Not a git repository: %s", dir);
+
+	update_linked_gitdir(path, dir);
 	path = real_path(dir);
 
 	free(buf);
diff --git a/t/t2026-prune-linked-checkouts.sh b/t/t2026-prune-linked-checkouts.sh
new file mode 100755
index 0000000..170aefe
--- /dev/null
+++ b/t/t2026-prune-linked-checkouts.sh
@@ -0,0 +1,84 @@
+#!/bin/sh
+
+test_description='prune $GIT_DIR/worktrees'
+
+. ./test-lib.sh
+
+test_expect_success 'prune --worktrees on normal repo' '
+	git prune --worktrees &&
+	test_must_fail git prune --worktrees abc
+'
+
+test_expect_success 'prune files inside $GIT_DIR/worktrees' '
+	mkdir .git/worktrees &&
+	: >.git/worktrees/abc &&
+	git prune --worktrees --verbose >actual &&
+	cat >expect <<EOF &&
+Removing worktrees/abc: not a valid directory
+EOF
+	test_i18ncmp expect actual &&
+	! test -f .git/worktrees/abc &&
+	! test -d .git/worktrees
+'
+
+test_expect_success 'prune directories without gitdir' '
+	mkdir -p .git/worktrees/def/abc &&
+	: >.git/worktrees/def/def &&
+	cat >expect <<EOF &&
+Removing worktrees/def: gitdir file does not exist
+EOF
+	git prune --worktrees --verbose >actual &&
+	test_i18ncmp expect actual &&
+	! test -d .git/worktrees/def &&
+	! test -d .git/worktrees
+'
+
+test_expect_success POSIXPERM 'prune directories with unreadable gitdir' '
+	mkdir -p .git/worktrees/def/abc &&
+	: >.git/worktrees/def/def &&
+	: >.git/worktrees/def/gitdir &&
+	chmod u-r .git/worktrees/def/gitdir &&
+	git prune --worktrees --verbose >actual &&
+	test_i18ngrep "Removing worktrees/def: unable to read gitdir file" actual &&
+	! test -d .git/worktrees/def &&
+	! test -d .git/worktrees
+'
+
+test_expect_success 'prune directories with invalid gitdir' '
+	mkdir -p .git/worktrees/def/abc &&
+	: >.git/worktrees/def/def &&
+	: >.git/worktrees/def/gitdir &&
+	git prune --worktrees --verbose >actual &&
+	test_i18ngrep "Removing worktrees/def: invalid gitdir file" actual &&
+	! test -d .git/worktrees/def &&
+	! test -d .git/worktrees
+'
+
+test_expect_success 'prune directories with gitdir pointing to nowhere' '
+	mkdir -p .git/worktrees/def/abc &&
+	: >.git/worktrees/def/def &&
+	echo "$(pwd)"/nowhere >.git/worktrees/def/gitdir &&
+	git prune --worktrees --verbose >actual &&
+	test_i18ngrep "Removing worktrees/def: gitdir file points to non-existent location" actual &&
+	! test -d .git/worktrees/def &&
+	! test -d .git/worktrees
+'
+
+test_expect_success 'not prune locked checkout' '
+	test_when_finished rm -r .git/worktrees
+	mkdir -p .git/worktrees/ghi &&
+	: >.git/worktrees/ghi/locked &&
+	git prune --worktrees &&
+	test -d .git/worktrees/ghi
+'
+
+test_expect_success 'not prune recent checkouts' '
+	test_when_finished rm -r .git/worktrees
+	mkdir zz &&
+	mkdir -p .git/worktrees/jlm &&
+	echo "$(pwd)"/zz >.git/worktrees/jlm/gitdir &&
+	git prune --worktrees --verbose --expire=2.days.ago &&
+	test -d .git/worktrees/jlm
+'
+
+test_done
-- 
2.1.0.rc0.78.gc0d8480

[PATCH 24/34] checkout: reject if the branch is already checked out elsewhere

[Nguyễn Thái Ngọc Duy]

One branch obviously can't be checked out at two places (but detached
heads are ok). Give the user a choice in this case: --detach, -b
new-branch, switch branch in the other checkout first or simply 'cd'
and continue to work there.

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
---
 builtin/checkout.c     | 86 ++++++++++++++++++++++++++++++++++++++++++++++++--
 t/t2025-checkout-to.sh | 25 ++++++++++++---
 2 files changed, 104 insertions(+), 7 deletions(-)

diff --git a/builtin/checkout.c b/builtin/checkout.c
index 645135a..01a28b4 100644
--- a/builtin/checkout.c
+++ b/builtin/checkout.c
@@ -430,6 +430,11 @@ struct branch_info {
 	const char *name; /* The short name used */
 	const char *path; /* The full name of a real branch */
 	struct commit *commit; /* The named commit */
+	/*
+	 * if not null the branch is detached because it's already
+	 * checked out in this checkout
+	 */
+	char *checkout;
 };
 
 static void setup_branch_path(struct branch_info *branch)
@@ -958,12 +963,78 @@ static const char *unique_tracking_name(const char *name, unsigned char *sha1)
 	return NULL;
 }
 
+static void check_linked_checkout(struct branch_info *new, const char *id)
+{
+	struct strbuf sb = STRBUF_INIT;
+	struct strbuf path = STRBUF_INIT;
+	struct strbuf gitdir = STRBUF_INIT;
+	const char *start, *end;
+
+	if (id)
+		strbuf_addf(&path, "%s/worktrees/%s/HEAD", get_git_common_dir(), id);
+	else
+		strbuf_addf(&path, "%s/HEAD", get_git_common_dir());
+
+	if (strbuf_read_file(&sb, path.buf, 0) < 0 ||
+	    !skip_prefix(sb.buf, "ref:", &start))
+		goto done;
+	while (isspace(*start))
+		start++;
+	end = start;
+	while (*end && !isspace(*end))
+		end++;
+	if (strncmp(start, new->path, end - start) || new->path[end - start] != '\0')
+		goto done;
+	if (id) {
+		strbuf_reset(&path);
+		strbuf_addf(&path, "%s/worktrees/%s/gitdir", get_git_common_dir(), id);
+		if (strbuf_read_file(&gitdir, path.buf, 0) <= 0)
+			goto done;
+		strbuf_rtrim(&gitdir);
+	} else
+		strbuf_addstr(&gitdir, get_git_common_dir());
+	die(_("'%s' is already checked out at '%s'"), new->name, gitdir.buf);
+done:
+	strbuf_release(&path);
+	strbuf_release(&sb);
+	strbuf_release(&gitdir);
+}
+
+static void check_linked_checkouts(struct branch_info *new)
+{
+	struct strbuf path = STRBUF_INIT;
+	DIR *dir;
+	struct dirent *d;
+
+	strbuf_addf(&path, "%s/worktrees", get_git_common_dir());
+	if ((dir = opendir(path.buf)) == NULL) {
+		strbuf_release(&path);
+		return;
+	}
+
+	/*
+	 * $GIT_COMMON_DIR/HEAD is practically outside
+	 * $GIT_DIR so resolve_ref_unsafe() won't work (it
+	 * uses git_path). Parse the ref ourselves.
+	 */
+	check_linked_checkout(new, NULL);
+
+	while ((d = readdir(dir)) != NULL) {
+		if (!strcmp(d->d_name, ".") || !strcmp(d->d_name, ".."))
+			continue;
+		check_linked_checkout(new, d->d_name);
+	}
+	strbuf_release(&path);
+	closedir(dir);
+}
+
 static int parse_branchname_arg(int argc, const char **argv,
 				int dwim_new_local_branch_ok,
 				struct branch_info *new,
 				struct tree **source_tree,
 				unsigned char rev[20],
-				const char **new_branch)
+				const char **new_branch,
+				int force_detach)
 {
 	int argcount = 0;
 	unsigned char branch_rev[20];
@@ -1085,6 +1156,16 @@ static int parse_branchname_arg(int argc, const char **argv,
 	else
 		new->path = NULL; /* not an existing branch */
 
+	if (new->path && !force_detach && !*new_branch) {
+		unsigned char sha1[20];
+		int flag;
+		char *head_ref = resolve_refdup("HEAD", 0, sha1, &flag);
+		if (head_ref &&
+		    (!(flag & REF_ISSYMREF) || strcmp(head_ref, new->path)))
+			check_linked_checkouts(new);
+		free(head_ref);
+	}
+
 	new->commit = lookup_commit_reference_gently(rev, 1);
 	if (!new->commit) {
 		/* not a commit */
@@ -1289,7 +1370,8 @@ int cmd_checkout(int argc, const char **argv, const char *prefix)
 			!opts.new_branch;
 		int n = parse_branchname_arg(argc, argv, dwim_ok,
 					     &new, &opts.source_tree,
-					     rev, &opts.new_branch);
+					     rev, &opts.new_branch,
+					     opts.force_detach);
 		argv += n;
 		argc -= n;
 	}
diff --git a/t/t2025-checkout-to.sh b/t/t2025-checkout-to.sh
index 4963415..edd3404 100755
--- a/t/t2025-checkout-to.sh
+++ b/t/t2025-checkout-to.sh
@@ -18,13 +18,14 @@ test_expect_success 'checkout --to an existing worktree' '
 '
 
 test_expect_success 'checkout --to a new worktree' '
-	git checkout --to here master &&
+	git rev-parse HEAD >expect &&
+	git checkout --detach --to here master &&
 	(
 		cd here &&
 		test_cmp ../init.t init.t &&
-		git symbolic-ref HEAD >actual &&
-		echo refs/heads/master >expect &&
-		test_cmp expect actual &&
+		test_must_fail git symbolic-ref HEAD &&
+		git rev-parse HEAD >actual &&
+		test_cmp ../expect actual &&
 		git fsck
 	)
 '
@@ -42,7 +43,7 @@ test_expect_success 'checkout --to a new worktree from a subdir' '
 test_expect_success 'checkout --to from a linked checkout' '
 	(
 		cd here &&
-		git checkout --to nested-here master &&
+		git checkout --detach --to nested-here master &&
 		cd nested-here &&
 		git fsck
 	)
@@ -60,4 +61,18 @@ test_expect_success 'checkout --to a new worktree creating new branch' '
 	)
 '
 
+test_expect_success 'die the same branch is already checked out' '
+	(
+		cd here &&
+		test_must_fail git checkout newmaster
+	)
+'
+
+test_expect_success 'not die on re-checking out current branch' '
+	(
+		cd there &&
+		git checkout newmaster
+	)
+'
+
 test_done
-- 
2.1.0.rc0.78.gc0d8480

[PATCH 25/34] checkout: clean up half-prepared directories in --to mode

[Nguyễn Thái Ngọc Duy]

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
---
 builtin/checkout.c     | 48 ++++++++++++++++++++++++++++++++++++++++++++++++
 t/t2025-checkout-to.sh |  6 ++++++
 2 files changed, 54 insertions(+)

diff --git a/builtin/checkout.c b/builtin/checkout.c
index 01a28b4..5dfdbda 100644
--- a/builtin/checkout.c
+++ b/builtin/checkout.c
@@ -20,6 +20,7 @@
 #include "resolve-undo.h"
 #include "submodule.h"
 #include "argv-array.h"
+#include "sigchain.h"
 
 static const char * const checkout_usage[] = {
 	N_("git checkout [options] <branch>"),
@@ -823,6 +824,35 @@ static int switch_branches(const struct checkout_opts *opts,
 	return ret || writeout_error;
 }
 
+static char *junk_work_tree;
+static char *junk_git_dir;
+static int is_junk;
+static pid_t junk_pid;
+
+static void remove_junk(void)
+{
+	struct strbuf sb = STRBUF_INIT;
+	if (!is_junk || getpid() != junk_pid)
+		return;
+	if (junk_git_dir) {
+		strbuf_addstr(&sb, junk_git_dir);
+		remove_dir_recursively(&sb, 0);
+		strbuf_reset(&sb);
+	}
+	if (junk_work_tree) {
+		strbuf_addstr(&sb, junk_work_tree);
+		remove_dir_recursively(&sb, 0);
+	}
+	strbuf_release(&sb);
+}
+
+static void remove_junk_on_signal(int signo)
+{
+	remove_junk();
+	sigchain_pop(signo);
+	raise(signo);
+}
+
 static int prepare_linked_checkout(const struct checkout_opts *opts,
 				   struct branch_info *new)
 {
@@ -859,8 +889,15 @@ static int prepare_linked_checkout(const struct checkout_opts *opts,
 		strbuf_addf(&sb_repo, "%d", counter);
 	}
 	name = strrchr(sb_repo.buf, '/') + 1;
+
+	junk_pid = getpid();
+	atexit(remove_junk);
+	sigchain_push_common(remove_junk_on_signal);
+
 	if (mkdir(sb_repo.buf, 0777))
 		die_errno(_("could not create directory of '%s'"), sb_repo.buf);
+	junk_git_dir = xstrdup(sb_repo.buf);
+	is_junk = 1;
 
 	/*
 	 * lock the incomplete repo so prune won't delete it, unlock
@@ -873,6 +910,7 @@ static int prepare_linked_checkout(const struct checkout_opts *opts,
 	if (safe_create_leading_directories_const(sb_git.buf))
 		die_errno(_("could not create leading directories of '%s'"),
 			  sb_git.buf);
+	junk_work_tree = xstrdup(path);
 
 	strbuf_reset(&sb);
 	strbuf_addf(&sb, "%s/gitdir", sb_repo.buf);
@@ -902,9 +940,19 @@ static int prepare_linked_checkout(const struct checkout_opts *opts,
 	cp.git_cmd = 1;
 	cp.argv = opts->saved_argv;
 	ret = run_command(&cp);
+	if (!ret) {
+		is_junk = 0;
+		free(junk_work_tree);
+		free(junk_git_dir);
+		junk_work_tree = NULL;
+		junk_git_dir = NULL;
+	}
 	strbuf_reset(&sb);
 	strbuf_addf(&sb, "%s/locked", sb_repo.buf);
 	unlink_or_warn(sb.buf);
+	strbuf_release(&sb);
+	strbuf_release(&sb_repo);
+	strbuf_release(&sb_git);
 	return ret;
 }
 
diff --git a/t/t2025-checkout-to.sh b/t/t2025-checkout-to.sh
index edd3404..e2db078 100755
--- a/t/t2025-checkout-to.sh
+++ b/t/t2025-checkout-to.sh
@@ -17,6 +17,12 @@ test_expect_success 'checkout --to an existing worktree' '
 	test_must_fail git checkout --detach --to existing master
 '
 
+test_expect_success 'checkout --to refuses to checkout locked branch' '
+	test_must_fail git checkout --to zere master &&
+	! test -d zere &&
+	! test -d .git/worktrees/zere
+'
+
 test_expect_success 'checkout --to a new worktree' '
 	git rev-parse HEAD >expect &&
 	git checkout --detach --to here master &&
-- 
2.1.0.rc0.78.gc0d8480

[PATCH 26/34] gc: style change -- no SP before closing parenthesis

[Nguyễn Thái Ngọc Duy]

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
---
 builtin/gc.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/builtin/gc.c b/builtin/gc.c
index 005adbe..0e65eff 100644
--- a/builtin/gc.c
+++ b/builtin/gc.c
@@ -287,7 +287,7 @@ int cmd_gc(int argc, const char **argv, const char *prefix)
 	argv_array_pushl(&pack_refs_cmd, "pack-refs", "--all", "--prune", NULL);
 	argv_array_pushl(&reflog, "reflog", "expire", "--all", NULL);
 	argv_array_pushl(&repack, "repack", "-d", "-l", NULL);
-	argv_array_pushl(&prune, "prune", "--expire", NULL );
+	argv_array_pushl(&prune, "prune", "--expire", NULL);
 	argv_array_pushl(&rerere, "rerere", "gc", NULL);
 
 	gc_config();
-- 
2.1.0.rc0.78.gc0d8480

[PATCH 27/34] gc: factor out gc.pruneexpire parsing code

[Nguyễn Thái Ngọc Duy]

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
---
 builtin/gc.c | 22 ++++++++++++----------
 1 file changed, 12 insertions(+), 10 deletions(-)

diff --git a/builtin/gc.c b/builtin/gc.c
index 0e65eff..0728650 100644
--- a/builtin/gc.c
+++ b/builtin/gc.c
@@ -55,6 +55,17 @@ static void remove_pidfile_on_signal(int signo)
 	raise(signo);
 }
 
+static void git_config_date_string(const char *key, const char **output)
+{
+	if (git_config_get_string_const(key, output))
+		return;
+	if (strcmp(*output, "now")) {
+		unsigned long now = approxidate("now");
+		if (approxidate(*output) >= now)
+			git_die_config(key, _("Invalid %s: '%s'"), key, *output);
+	}
+}
+
 static void gc_config(void)
 {
 	const char *value;
@@ -71,16 +82,7 @@ static void gc_config(void)
 	git_config_get_int("gc.auto", &gc_auto_threshold);
 	git_config_get_int("gc.autopacklimit", &gc_auto_pack_limit);
 	git_config_get_bool("gc.autodetach", &detach_auto);
-
-	if (!git_config_get_string_const("gc.pruneexpire", &prune_expire)) {
-		if (strcmp(prune_expire, "now")) {
-			unsigned long now = approxidate("now");
-			if (approxidate(prune_expire) >= now) {
-				git_die_config("gc.pruneexpire", _("Invalid gc.pruneexpire: '%s'"),
-						prune_expire);
-			}
-		}
-	}
+	git_config_date_string("gc.pruneexpire", &prune_expire);
 	git_config(git_default_config, NULL);
 }
 
-- 
2.1.0.rc0.78.gc0d8480

[PATCH 28/34] gc: support prune --worktrees

[Nguyễn Thái Ngọc Duy]

Helped-by: Marc Branchaud <marcnarc@xiplink.com>
Signed-off-by: Marc Branchaud <marcnarc@xiplink.com>
Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
---
 Documentation/config.txt       |  7 +++++++
 Documentation/git-checkout.txt | 11 +++++++----
 builtin/gc.c                   | 10 ++++++++++
 3 files changed, 24 insertions(+), 4 deletions(-)

diff --git a/Documentation/config.txt b/Documentation/config.txt
index e1623ec..2700a1b 100644
--- a/Documentation/config.txt
+++ b/Documentation/config.txt
@@ -1229,6 +1229,13 @@ gc.pruneexpire::
 	"now" may be used to disable this  grace period and always prune
 	unreachable objects immediately.
 
+gc.pruneworktreesexpire::
+	When 'git gc' is run, it will call
+	'prune --worktrees --expire 3.months.ago'.
+	Override the grace period with this config variable. The value
+	"now" may be used to disable the grace period and prune
+	$GIT_DIR/worktrees immediately.
+
 gc.reflogexpire::
 gc.<pattern>.reflogexpire::
 	'git reflog expire' removes reflog entries older than
diff --git a/Documentation/git-checkout.txt b/Documentation/git-checkout.txt
index 35675da..0c13825 100644
--- a/Documentation/git-checkout.txt
+++ b/Documentation/git-checkout.txt
@@ -435,8 +435,11 @@ $GIT_DIR or $GIT_COMMON_DIR when you need to directly access something
 inside $GIT_DIR. Use `git rev-parse --git-path` to get the final path.
 
 When you are done with a linked working tree you can simply delete it.
-You can clean up any stale $GIT_DIR/worktrees entries via `git prune
---worktrees` in the main or any linked working tree.
+The working tree's entry in the repository's $GIT_DIR/worktrees
+directory will eventually be removed automatically (see
+`gc.pruneworktreesexpire` in linkgit::git-config[1]), or you can run
+`git prune --worktrees` in the main or any linked working tree to
+clean up any stale entries in $GIT_DIR/worktrees.
 
 If you move a linked working directory to another file system, or
 within a file system that does not support hard links, you need to run
@@ -444,8 +447,8 @@ at least one git command inside the linked working directory
 (e.g. `git status`) in order to update its entry in $GIT_DIR/worktrees
 so that it does not get automatically removed.
 
-To prevent `git prune --worktrees` from deleting a $GIT_DIR/worktrees
-entry (which can be useful in some situations, such as when the
+To prevent a $GIT_DIR/worktrees entry from from being pruned (which
+can be useful in some situations, such as when the
 entry's working tree is stored on a portable device), add a file named
 'locked' to the entry's directory. The file contains the reason in
 plain text. For example, if a linked working tree's `.git` file points
diff --git a/builtin/gc.c b/builtin/gc.c
index 0728650..fa87ad3 100644
--- a/builtin/gc.c
+++ b/builtin/gc.c
@@ -33,11 +33,13 @@ static int gc_auto_threshold = 6700;
 static int gc_auto_pack_limit = 50;
 static int detach_auto = 1;
 static const char *prune_expire = "2.weeks.ago";
+static const char *prune_worktrees_expire = "3.months.ago";
 
 static struct argv_array pack_refs_cmd = ARGV_ARRAY_INIT;
 static struct argv_array reflog = ARGV_ARRAY_INIT;
 static struct argv_array repack = ARGV_ARRAY_INIT;
 static struct argv_array prune = ARGV_ARRAY_INIT;
+static struct argv_array prune_worktrees = ARGV_ARRAY_INIT;
 static struct argv_array rerere = ARGV_ARRAY_INIT;
 
 static char *pidfile;
@@ -83,6 +85,7 @@ static void gc_config(void)
 	git_config_get_int("gc.autopacklimit", &gc_auto_pack_limit);
 	git_config_get_bool("gc.autodetach", &detach_auto);
 	git_config_date_string("gc.pruneexpire", &prune_expire);
+	git_config_date_string("gc.pruneworktreesexpire", &prune_worktrees_expire);
 	git_config(git_default_config, NULL);
 }
 
@@ -290,6 +293,7 @@ int cmd_gc(int argc, const char **argv, const char *prefix)
 	argv_array_pushl(&reflog, "reflog", "expire", "--all", NULL);
 	argv_array_pushl(&repack, "repack", "-d", "-l", NULL);
 	argv_array_pushl(&prune, "prune", "--expire", NULL);
+	argv_array_pushl(&prune_worktrees, "prune", "--worktrees", "--expire", NULL);
 	argv_array_pushl(&rerere, "rerere", "gc", NULL);
 
 	gc_config();
@@ -359,6 +363,12 @@ int cmd_gc(int argc, const char **argv, const char *prefix)
 			return error(FAILED_RUN, prune.argv[0]);
 	}
 
+	if (prune_worktrees_expire) {
+		argv_array_push(&prune_worktrees, prune_worktrees_expire);
+		if (run_command_v_opt(prune_worktrees.argv, RUN_GIT_CMD))
+			return error(FAILED_RUN, prune_worktrees.argv[0]);
+	}
+
 	if (run_command_v_opt(rerere.argv, RUN_GIT_CMD))
 		return error(FAILED_RUN, rerere.argv[0]);
 
-- 
2.1.0.rc0.78.gc0d8480

[PATCH 29/34] count-objects: report unused files in $GIT_DIR/worktrees/...

[Nguyễn Thái Ngọc Duy]

In linked checkouts, borrowed parts like config is taken from
$GIT_COMMON_DIR. $GIT_DIR/config is never used. Report them as
garbage.

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
---
 builtin/count-objects.c |  4 +++-
 cache.h                 |  1 +
 path.c                  | 29 +++++++++++++++++++++++++++--
 3 files changed, 31 insertions(+), 3 deletions(-)

diff --git a/builtin/count-objects.c b/builtin/count-objects.c
index e47ef0b..ad0c799 100644
--- a/builtin/count-objects.c
+++ b/builtin/count-objects.c
@@ -70,8 +70,10 @@ int cmd_count_objects(int argc, const char **argv, const char *prefix)
 	/* we do not take arguments other than flags for now */
 	if (argc)
 		usage_with_options(count_objects_usage, opts);
-	if (verbose)
+	if (verbose) {
 		report_garbage = real_report_garbage;
+		report_linked_checkout_garbage();
+	}
 
 	for_each_loose_file_in_objdir(get_object_directory(),
 				      count_loose, count_cruft, NULL, NULL);
diff --git a/cache.h b/cache.h
index f8e75a1..3f60a11 100644
--- a/cache.h
+++ b/cache.h
@@ -695,6 +695,7 @@ extern const char *mkpath(const char *fmt, ...) __attribute__((format (printf, 1
 extern const char *git_path(const char *fmt, ...) __attribute__((format (printf, 1, 2)));
 extern const char *git_path_submodule(const char *path, const char *fmt, ...)
 	__attribute__((format (printf, 2, 3)));
+extern void report_linked_checkout_garbage(void);
 
 /*
  * Return the name of the file in the local object database that would
diff --git a/path.c b/path.c
index 72eca6d..cd8e2d6 100644
--- a/path.c
+++ b/path.c
@@ -4,6 +4,7 @@
 #include "cache.h"
 #include "strbuf.h"
 #include "string-list.h"
+#include "dir.h"
 
 static int get_st_mode_bits(const char *path, int *mode)
 {
@@ -91,9 +92,9 @@ static void replace_dir(struct strbuf *buf, int len, const char *newdir)
 }
 
 static const char *common_list[] = {
-	"/branches", "/hooks", "/info", "/logs", "/lost-found", "/modules",
+	"/branches", "/hooks", "/info", "!/logs", "/lost-found", "/modules",
 	"/objects", "/refs", "/remotes", "/worktrees", "/rr-cache", "/svn",
-	"config", "gc.pid", "packed-refs", "shallow",
+	"config", "!gc.pid", "packed-refs", "shallow",
 	NULL
 };
 
@@ -107,6 +108,8 @@ static void update_common_dir(struct strbuf *buf, int git_dir_len)
 	for (p = common_list; *p; p++) {
 		const char *path = *p;
 		int is_dir = 0;
+		if (*path == '!')
+			path++;
 		if (*path == '/') {
 			path++;
 			is_dir = 1;
@@ -122,6 +125,28 @@ static void update_common_dir(struct strbuf *buf, int git_dir_len)
 	}
 }
 
+void report_linked_checkout_garbage(void)
+{
+	struct strbuf sb = STRBUF_INIT;
+	const char **p;
+	int len;
+
+	if (!git_common_dir_env)
+		return;
+	strbuf_addf(&sb, "%s/", get_git_dir());
+	len = sb.len;
+	for (p = common_list; *p; p++) {
+		const char *path = *p;
+		if (*path == '!')
+			continue;
+		strbuf_setlen(&sb, len);
+		strbuf_addstr(&sb, path);
+		if (file_exists(sb.buf))
+			report_garbage("unused in linked checkout", sb.buf);
+	}
+	strbuf_release(&sb);
+}
+
 static void adjust_git_path(struct strbuf *buf, int git_dir_len)
 {
 	const char *base = buf->buf + git_dir_len;
-- 
2.1.0.rc0.78.gc0d8480

[PATCH 30/34] git_path(): keep "info/sparse-checkout" per work-tree

[Nguyễn Thái Ngọc Duy]

Currently git_path("info/sparse-checkout") resolves to
$GIT_COMMON_DIR/info/sparse-checkout in multiple worktree mode. It
makes more sense for the sparse checkout patterns to be per worktree,
so you can have multiple checkouts with different parts of the tree.

With this, "git checkout --to <new>" on a sparse checkout will create
<new> as a full checkout. Which is expected, it's how a new checkout
is made. The user can reshape the worktree afterwards.

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
---
 path.c                | 3 ++-
 t/t0060-path-utils.sh | 1 +
 2 files changed, 3 insertions(+), 1 deletion(-)

diff --git a/path.c b/path.c
index cd8e2d6..35d498e 100644
--- a/path.c
+++ b/path.c
@@ -103,7 +103,8 @@ static void update_common_dir(struct strbuf *buf, int git_dir_len)
 	char *base = buf->buf + git_dir_len;
 	const char **p;
 
-	if (is_dir_file(base, "logs", "HEAD"))
+	if (is_dir_file(base, "logs", "HEAD") ||
+	    is_dir_file(base, "info", "sparse-checkout"))
 		return;	/* keep this in $GIT_DIR */
 	for (p = common_list; *p; p++) {
 		const char *path = *p;
diff --git a/t/t0060-path-utils.sh b/t/t0060-path-utils.sh
index f5d6f80..93605f4 100755
--- a/t/t0060-path-utils.sh
+++ b/t/t0060-path-utils.sh
@@ -270,6 +270,7 @@ test_git_path GIT_COMMON_DIR=bar objects                  bar/objects
 test_git_path GIT_COMMON_DIR=bar objects/bar              bar/objects/bar
 test_git_path GIT_COMMON_DIR=bar info/exclude             bar/info/exclude
 test_git_path GIT_COMMON_DIR=bar info/grafts              bar/info/grafts
+test_git_path GIT_COMMON_DIR=bar info/sparse-checkout     .git/info/sparse-checkout
 test_git_path GIT_COMMON_DIR=bar remotes/bar              bar/remotes/bar
 test_git_path GIT_COMMON_DIR=bar branches/bar             bar/branches/bar
 test_git_path GIT_COMMON_DIR=bar logs/refs/heads/master   bar/logs/refs/heads/master
-- 
2.1.0.rc0.78.gc0d8480

[PATCH 31/34] checkout: don't require a work tree when checking out into a new one

[Nguyễn Thái Ngọc Duy]

From: Dennis Kaarsemaker <dennis@kaarsemaker.net>

For normal use cases, it does not make sense for 'checkout' to work on
a bare repository, without a worktree. But "checkout --to" is an
exception because it _creates_ a new worktree. Allow this option to
run on bare repositories.

People who check out from a bare repository should remember that
core.logallrefupdates is off by default and it should be turned back
on. `--to` cannot do this automatically behind the user's back because
some user may deliberately want no reflog.

For people interested in repository setup/discovery code,
is_bare_repository_cfg (aka "core.bare") is unchanged by this patch,
which means 'true' by default for bare repos. Fortunately when we get
the repo through a linked checkout, is_bare_repository_cfg is never
used. So all is still good.

[nd: commit message]

Signed-off-by: Dennis Kaarsemaker <dennis@kaarsemaker.net>
Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
---
 builtin/checkout.c     |  3 +++
 git.c                  |  2 +-
 t/t2025-checkout-to.sh | 15 +++++++++++++++
 3 files changed, 19 insertions(+), 1 deletion(-)

diff --git a/builtin/checkout.c b/builtin/checkout.c
index 5dfdbda..8c5276c 100644
--- a/builtin/checkout.c
+++ b/builtin/checkout.c
@@ -1364,6 +1364,9 @@ int cmd_checkout(int argc, const char **argv, const char *prefix)
 	if (opts.new_worktree_mode)
 		opts.new_worktree = NULL;
 
+	if (!opts.new_worktree)
+		setup_work_tree();
+
 	if (conflict_style) {
 		opts.merge = 1; /* implied */
 		git_xmerge_config("merge.conflictstyle", conflict_style, NULL);
diff --git a/git.c b/git.c
index 18fbf79..160896a 100644
--- a/git.c
+++ b/git.c
@@ -383,7 +383,7 @@ static struct cmd_struct commands[] = {
 	{ "check-ignore", cmd_check_ignore, RUN_SETUP | NEED_WORK_TREE },
 	{ "check-mailmap", cmd_check_mailmap, RUN_SETUP },
 	{ "check-ref-format", cmd_check_ref_format },
-	{ "checkout", cmd_checkout, RUN_SETUP | NEED_WORK_TREE },
+	{ "checkout", cmd_checkout, RUN_SETUP },
 	{ "checkout-index", cmd_checkout_index,
 		RUN_SETUP | NEED_WORK_TREE},
 	{ "cherry", cmd_cherry, RUN_SETUP },
diff --git a/t/t2025-checkout-to.sh b/t/t2025-checkout-to.sh
index e2db078..4bd1df4 100755
--- a/t/t2025-checkout-to.sh
+++ b/t/t2025-checkout-to.sh
@@ -81,4 +81,19 @@ test_expect_success 'not die on re-checking out current branch' '
 	)
 '
 
+test_expect_success 'checkout --to from a bare repo' '
+	(
+		git clone --bare . bare &&
+		cd bare &&
+		git checkout --to ../there2 -b bare-master master
+	)
+'
+
+test_expect_success 'checkout from a bare repo without --to' '
+	(
+		cd bare &&
+		test_must_fail git checkout master
+	)
+'
+
 test_done
-- 
2.1.0.rc0.78.gc0d8480

[PATCH 32/34] t2025: add a test to make sure grafts is working from a linked checkout

[Nguyễn Thái Ngọc Duy]

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
---
 t/t2025-checkout-to.sh | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/t/t2025-checkout-to.sh b/t/t2025-checkout-to.sh
index 4bd1df4..eddd325 100755
--- a/t/t2025-checkout-to.sh
+++ b/t/t2025-checkout-to.sh
@@ -96,4 +96,22 @@ test_expect_success 'checkout from a bare repo without --to' '
 	)
 '
 
+test_expect_success 'checkout with grafts' '
+	test_when_finished rm .git/info/grafts &&
+	test_commit abc &&
+	SHA1=`git rev-parse HEAD` &&
+	test_commit def &&
+	test_commit xyz &&
+	echo "`git rev-parse HEAD` $SHA1" >.git/info/grafts &&
+	cat >expected <<-\EOF &&
+	xyz
+	abc
+	EOF
+	git log --format=%s -2 >actual &&
+	test_cmp expected actual &&
+	git checkout --detach --to grafted master &&
+	git --git-dir=grafted/.git log --format=%s -2 >actual &&
+	test_cmp expected actual
+'
+
 test_done
-- 
2.1.0.rc0.78.gc0d8480

[PATCH 33/34] checkout: do not fail if target is an empty directory

[Nguyễn Thái Ngọc Duy]

From: Max Kirillov <max@max630.net>

Non-recursive checkout creates empty directpries in place of submodules.
If then I try to "checkout --to" submodules there, it refuses to do so,
because directory already exists.

Fix by allowing checking out to empty directory. Add test and modify the
existing one so that it uses non-empty directory.

Signed-off-by: Max Kirillov <max@max630.net>
Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
---
 builtin/checkout.c     | 2 +-
 t/t2025-checkout-to.sh | 7 ++++++-
 2 files changed, 7 insertions(+), 2 deletions(-)

diff --git a/builtin/checkout.c b/builtin/checkout.c
index 8c5276c..953b763 100644
--- a/builtin/checkout.c
+++ b/builtin/checkout.c
@@ -865,7 +865,7 @@ static int prepare_linked_checkout(const struct checkout_opts *opts,
 
 	if (!new->commit)
 		die(_("no branch specified"));
-	if (file_exists(path))
+	if (file_exists(path) && !is_empty_dir(path))
 		die(_("'%s' already exists"), path);
 
 	len = strlen(path);
diff --git a/t/t2025-checkout-to.sh b/t/t2025-checkout-to.sh
index eddd325..915b506 100755
--- a/t/t2025-checkout-to.sh
+++ b/t/t2025-checkout-to.sh
@@ -13,10 +13,15 @@ test_expect_success 'checkout --to not updating paths' '
 '
 
 test_expect_success 'checkout --to an existing worktree' '
-	mkdir existing &&
+	mkdir -p existing/subtree &&
 	test_must_fail git checkout --detach --to existing master
 '
 
+test_expect_success 'checkout --to an existing empty worktree' '
+	mkdir existing_empty &&
+	git checkout --detach --to existing_empty master
+'
+
 test_expect_success 'checkout --to refuses to checkout locked branch' '
 	test_must_fail git checkout --to zere master &&
 	! test -d zere &&
-- 
2.1.0.rc0.78.gc0d8480

[PATCH 34/34] git-common-dir: make "modules/" per-working-directory directory

[Nguyễn Thái Ngọc Duy]

From: Max Kirillov <max@max630.net>

Each working directory of main repository has its own working directory
of submodule, and in most cases they should be checked out to different
revisions. So they should be separated.

It looks logical to make submodule instances in different working
directories to reuse the submodule directory in the common dir of
the main repository, and probably this is how "checkout --to" should
initialize them called on the main repository, but they also should work
fine being completely separated clones.

Testfile t7410-submodule-checkout-to.sh demostrates the behavior.

Signed-off-by: Max Kirillov <max@max630.net>
Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
---
 Documentation/gitrepository-layout.txt    |  4 +--
 path.c                                    |  2 +-
 t/t7410-submodule-checkout-to.sh (new +x) | 50 +++++++++++++++++++++++++++++++
 3 files changed, 52 insertions(+), 4 deletions(-)
 create mode 100755 t/t7410-submodule-checkout-to.sh

diff --git a/Documentation/gitrepository-layout.txt b/Documentation/gitrepository-layout.txt
index 2b30a92..7173b38 100644
--- a/Documentation/gitrepository-layout.txt
+++ b/Documentation/gitrepository-layout.txt
@@ -248,9 +248,7 @@ commondir::
 	incomplete without the repository pointed by "commondir".
 
 modules::
-	Contains the git-repositories of the submodules. This
-	directory is ignored if $GIT_COMMON_DIR is set and
-	"$GIT_COMMON_DIR/modules" will be used instead.
+	Contains the git-repositories of the submodules.
 
 worktrees::
 	Contains worktree specific information of linked
diff --git a/path.c b/path.c
index 35d498e..a5c51a3 100644
--- a/path.c
+++ b/path.c
@@ -92,7 +92,7 @@ static void replace_dir(struct strbuf *buf, int len, const char *newdir)
 }
 
 static const char *common_list[] = {
-	"/branches", "/hooks", "/info", "!/logs", "/lost-found", "/modules",
+	"/branches", "/hooks", "/info", "!/logs", "/lost-found",
 	"/objects", "/refs", "/remotes", "/worktrees", "/rr-cache", "/svn",
 	"config", "!gc.pid", "packed-refs", "shallow",
 	NULL
diff --git a/t/t7410-submodule-checkout-to.sh b/t/t7410-submodule-checkout-to.sh
new file mode 100755
index 0000000..8f30aed
--- /dev/null
+++ b/t/t7410-submodule-checkout-to.sh
@@ -0,0 +1,50 @@
+#!/bin/sh
+
+test_description='Combination of submodules and multiple workdirs'
+
+. ./test-lib.sh
+
+base_path=$(pwd -P)
+
+test_expect_success 'setup: make origin' \
+    'mkdir -p origin/sub && ( cd origin/sub && git init &&
+	echo file1 >file1 &&
+	git add file1 &&
+	git commit -m file1 ) &&
+    mkdir -p origin/main && ( cd origin/main && git init &&
+	git submodule add ../sub &&
+	git commit -m "add sub" ) &&
+    ( cd origin/sub &&
+	echo file1updated >file1 &&
+	git add file1 &&
+	git commit -m "file1 updated" ) &&
+    ( cd origin/main/sub && git pull ) &&
+    ( cd origin/main &&
+	git add sub &&
+	git commit -m "sub updated" )'
+
+test_expect_success 'setup: clone' \
+    'mkdir clone && ( cd clone &&
+	git clone --recursive "$base_path/origin/main")'
+
+rev1_hash_main=$(git --git-dir=origin/main/.git show --pretty=format:%h -q "HEAD~1")
+rev1_hash_sub=$(git --git-dir=origin/sub/.git show --pretty=format:%h -q "HEAD~1")
+
+test_expect_success 'checkout main' \
+    'mkdir default_checkout &&
+    (cd clone/main &&
+	git checkout --to "$base_path/default_checkout/main" "$rev1_hash_main")'
+
+test_expect_failure 'can see submodule diffs just after checkout' \
+    '(cd default_checkout/main && git diff --submodule master"^!" | grep "file1 updated")'
+
+test_expect_success 'checkout main and initialize independed clones' \
+    'mkdir fully_cloned_submodule &&
+    (cd clone/main &&
+	git checkout --to "$base_path/fully_cloned_submodule/main" "$rev1_hash_main") &&
+    (cd fully_cloned_submodule/main && git submodule update)'
+
+test_expect_success 'can see submodule diffs after independed cloning' \
+    '(cd fully_cloned_submodule/main && git diff --submodule master"^!" | grep "file1 updated")'
+
+test_done
-- 
2.1.0.rc0.78.gc0d8480

Re: [PATCH 24/34] checkout: reject if the branch is already checked out elsewhere

[Mark Levedahl]

On 11/30/2014 03:24 AM, Nguyễn Thái Ngọc Duy wrote:
> One branch obviously can't be checked out at two places (but detached
> heads are ok). Give the user a choice in this case: --detach, -b
> new-branch, switch branch in the other checkout first or simply 'cd'
> and continue to work there.
>

This seems too restrictive and is not "obvious" to me: I currently use 
git-new-workdir to have multiple checkouts of the same branch, with no 
ill effect. While those who do not understand what is going on 
underneath might be confused by one checkout suddenly showing 
uncommitted diffs, I don't accept that as a reason to outright prevent 
such use. I suggest, at the very least, that this behavior be overridden 
by a --force flag?

Mark

Re: [PATCH 24/34] checkout: reject if the branch is already checked out elsewhere

[Duy Nguyen]

On Sun, Nov 30, 2014 at 12:18:40PM -0500, Mark Levedahl wrote:
> On 11/30/2014 03:24 AM, Nguyễn Thái Ngọc Duy wrote:
> > One branch obviously can't be checked out at two places (but detached
> > heads are ok). Give the user a choice in this case: --detach, -b
> > new-branch, switch branch in the other checkout first or simply 'cd'
> > and continue to work there.
> >
> 
> This seems too restrictive and is not "obvious" to me: I currently use 
> git-new-workdir to have multiple checkouts of the same branch, with no 
> ill effect. While those who do not understand what is going on 
> underneath might be confused by one checkout suddenly showing 
> uncommitted diffs, I don't accept that as a reason to outright prevent 
> such use. I suggest, at the very least, that this behavior be overridden 
> by a --force flag?

Prevention is a strong word. It's more about safety for the mere
mortals. It's certainly possible to do something like this patch
(--force can't be reused, it already carries some other meaning).
Should I add this one in the next (hic) reroll?

-- 8< --
Subject: [PATCH] checkout: add --ignore-other-wortrees

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
---
 Documentation/git-checkout.txt |  6 ++++++
 builtin/checkout.c             | 19 +++++++++++--------
 t/t2025-checkout-to.sh         |  7 +++++++
 3 files changed, 24 insertions(+), 8 deletions(-)

diff --git a/Documentation/git-checkout.txt b/Documentation/git-checkout.txt
index 0c13825..71d9e4e 100644
--- a/Documentation/git-checkout.txt
+++ b/Documentation/git-checkout.txt
@@ -232,6 +232,12 @@ section of linkgit:git-add[1] to learn how to operate the `--patch` mode.
 	specific files such as HEAD, index... See "MULTIPLE WORKING
 	TREES" section for more information.
 
+--ignore-other-worktrees::
+	`git checkout` refuses when the wanted ref is already checked out
+	by another worktree. This option makes it check the
+	ref out anyway. In other words, the ref is held by more than one
+	worktree.
+
 <branch>::
 	Branch to checkout; if it refers to a branch (i.e., a name that,
 	when prepended with "refs/heads/", is a valid ref), then that
diff --git a/builtin/checkout.c b/builtin/checkout.c
index 953b763..8b2bf20 100644
--- a/builtin/checkout.c
+++ b/builtin/checkout.c
@@ -37,6 +37,7 @@ struct checkout_opts {
 	int writeout_stage;
 	int overwrite_ignore;
 	int ignore_skipworktree;
+	int ignore_other_worktrees;
 
 	const char *new_branch;
 	const char *new_branch_force;
@@ -1079,11 +1080,12 @@ static void check_linked_checkouts(struct branch_info *new)
 static int parse_branchname_arg(int argc, const char **argv,
 				int dwim_new_local_branch_ok,
 				struct branch_info *new,
-				struct tree **source_tree,
-				unsigned char rev[20],
-				const char **new_branch,
-				int force_detach)
+				struct checkout_opts *opts,
+				unsigned char rev[20])
 {
+	struct tree **source_tree = &opts->source_tree;
+	const char **new_branch = &opts->new_branch;
+	int force_detach = opts->force_detach;
 	int argcount = 0;
 	unsigned char branch_rev[20];
 	const char *arg;
@@ -1209,7 +1211,8 @@ static int parse_branchname_arg(int argc, const char **argv,
 		int flag;
 		char *head_ref = resolve_refdup("HEAD", 0, sha1, &flag);
 		if (head_ref &&
-		    (!(flag & REF_ISSYMREF) || strcmp(head_ref, new->path)))
+		    (!(flag & REF_ISSYMREF) || strcmp(head_ref, new->path)) &&
+		    !opts->ignore_other_worktrees)
 			check_linked_checkouts(new);
 		free(head_ref);
 	}
@@ -1340,6 +1343,8 @@ int cmd_checkout(int argc, const char **argv, const char *prefix)
 				N_("second guess 'git checkout no-such-branch'")),
 		OPT_FILENAME(0, "to", &opts.new_worktree,
 			   N_("check a branch out in a separate working directory")),
+		OPT_BOOL(0, "ignore-other-worktrees", &opts.ignore_other_worktrees,
+			 N_("do not check if another worktree is holding the given ref")),
 		OPT_END(),
 	};
 
@@ -1420,9 +1425,7 @@ int cmd_checkout(int argc, const char **argv, const char *prefix)
 			opts.track == BRANCH_TRACK_UNSPECIFIED &&
 			!opts.new_branch;
 		int n = parse_branchname_arg(argc, argv, dwim_ok,
-					     &new, &opts.source_tree,
-					     rev, &opts.new_branch,
-					     opts.force_detach);
+					     &new, &opts, rev);
 		argv += n;
 		argc -= n;
 	}
diff --git a/t/t2025-checkout-to.sh b/t/t2025-checkout-to.sh
index 915b506..f8e4df4 100755
--- a/t/t2025-checkout-to.sh
+++ b/t/t2025-checkout-to.sh
@@ -79,6 +79,13 @@ test_expect_success 'die the same branch is already checked out' '
 	)
 '
 
+test_expect_success 'not die the same branch is already checked out' '
+	(
+		cd here &&
+		git checkout --ignore-other-worktrees --to anothernewmaster newmaster
+	)
+'
+
 test_expect_success 'not die on re-checking out current branch' '
 	(
 		cd there &&
-- 
2.2.0.60.gb7b3c64

-- 8< --

Re: [PATCH 24/34] checkout: reject if the branch is already checked out elsewhere

[Junio C Hamano]

Duy Nguyen <pclouds@gmail.com> writes:

> On Sun, Nov 30, 2014 at 12:18:40PM -0500, Mark Levedahl wrote:
>> On 11/30/2014 03:24 AM, Nguyễn Thái Ngọc Duy wrote:
>> > One branch obviously can't be checked out at two places (but detached
>> > heads are ok). Give the user a choice in this case: --detach, -b
>> > new-branch, switch branch in the other checkout first or simply 'cd'
>> > and continue to work there.
>> >
>> 
>> This seems too restrictive and is not "obvious" to me: I currently use 
>> git-new-workdir to have multiple checkouts of the same branch, with no 
>> ill effect. While those who do not understand what is going on 
>> underneath might be confused by one checkout suddenly showing 
>> uncommitted diffs, I don't accept that as a reason to outright prevent 
>> such use. I suggest, at the very least, that this behavior be overridden 
>> by a --force flag?
>
> Prevention is a strong word. It's more about safety for the mere
> mortals. It's certainly possible to do something like this patch
> (--force can't be reused, it already carries some other meaning).
> Should I add this one in the next (hic) reroll?

Sorry, what is a hic?

If this were an existing feature like git-new-workdir, even though
it is from contrib, making it impossible to do something that used
to be possible, even if that something is what mere mortals would
never want to to to avoid risking confusion, would be a regression
that needs an escape hatch.

But this is a new feature.  I am not sure why you need to make this
overridable in the first place.  Those who want to have multiple
checkouts of the same commit can just detach HEAD at the same commit
in multiple working trees, as the first thing they need to do would
be to run "git reset --hard $branch" to synchronize the HEAD and the
working tree state to work in the other out-of-sync repositories
either case anyway.

Re: [PATCH 24/34] checkout: reject if the branch is already checked out elsewhere

[Mark Levedahl]

On 12/01/2014 12:39 PM, Junio C Hamano wrote:
> Sorry, what is a hic? If this were an existing feature like 
> git-new-workdir, even though it is from contrib, making it impossible 
> to do something that used to be possible, even if that something is 
> what mere mortals would never want to to to avoid risking confusion, 
> would be a regression that needs an escape hatch. But this is a new 
> feature. I am not sure why you need to make this overridable in the 
> first place. Those who want to have multiple checkouts of the same 
> commit can just detach HEAD at the same commit in multiple working 
> trees, as the first thing they need to do would be to run "git reset 
> --hard $branch" to synchronize the HEAD and the working tree state to 
> work in the other out-of-sync repositories either case anyway. 

Yes, detached HEADS allow multiple checkouts, but now the user needs 
another system to record what $branch was for each checked out tree or 
needs to resort to forensics using various git-branch / git-log 
invocations to find the most-likely value. So, I do not find detached 
HEADS useful in general, and specifically not for this case. Duy's 
latest addition ('--ignore-other-worktrees') would, so far as I see, 
allow this feature to replace git-new-workdir in my uses, but without 
the addition it cannot.

Mark

Re: [PATCH 24/34] checkout: reject if the branch is already checked out elsewhere

[Duy Nguyen]

On Tue, Dec 2, 2014 at 12:39 AM, Junio C Hamano <gitster@pobox.com> wrote:
> Sorry, what is a hic?

Off topic. It's the sound (in Vietnamese) when you inhale through your
nose, e.g. like when you cry.. I know there's an equivalent in
English, just can't remember it now.
-- 
Duy

Re: [PATCH 24/34] checkout: reject if the branch is already checked out elsewhere

[Duy Nguyen]

On Tue, Dec 2, 2014 at 12:04 PM, Mark Levedahl <mlevedahl@gmail.com> wrote:
> On 12/01/2014 12:39 PM, Junio C Hamano wrote:
>>
>> Sorry, what is a hic? If this were an existing feature like
>> git-new-workdir, even though it is from contrib, making it impossible to do
>> something that used to be possible, even if that something is what mere
>> mortals would never want to to to avoid risking confusion, would be a
>> regression that needs an escape hatch. But this is a new feature. I am not
>> sure why you need to make this overridable in the first place. Those who
>> want to have multiple checkouts of the same commit can just detach HEAD at
>> the same commit in multiple working trees, as the first thing they need to
>> do would be to run "git reset --hard $branch" to synchronize the HEAD and
>> the working tree state to work in the other out-of-sync repositories either
>> case anyway.
>
>
> Yes, detached HEADS allow multiple checkouts, but now the user needs another
> system to record what $branch was for each checked out tree or needs to
> resort to forensics using various git-branch / git-log invocations to find
> the most-likely value. So, I do not find detached HEADS useful in general,
> and specifically not for this case. Duy's latest addition
> ('--ignore-other-worktrees') would, so far as I see, allow this feature to
> replace git-new-workdir in my uses, but without the addition it cannot.

I'm ok either way. So I'll let you and Junio (and maybe others) sort
this out. No objection means --ignore-other-worktrees is in.

FWIW git-branch usually can show the original branch of detached head
(must not always). I don't think we have a plumbing equivalent for it
though. People can "tail -1 $GIT_DIR/logs/HEAD| sed .." but that seems
hacky. I do like "read-only" ref concept where we can keep ref name
(especially tags) in HEAD until the next commit. But it didn't go
anywhere
-- 
Duy

Re: [PATCH 24/34] checkout: reject if the branch is already checked out elsewhere

[Junio C Hamano]

Duy Nguyen <pclouds@gmail.com> writes:

> FWIW git-branch usually can show the original branch of detached head
> (must not always). I don't think we have a plumbing equivalent for it
> though. People can "tail -1 $GIT_DIR/logs/HEAD| sed .." but that seems
> hacky.

@{-1}, i.e. "the last branch I checked out"?

> I do like "read-only" ref concept where we can keep ref name
> (especially tags) in HEAD until the next commit. But it didn't go
> anywhere

Remind me.  That sounds somewhat interesting.

Re: [PATCH 24/34] checkout: reject if the branch is already checked out elsewhere

[Mark Levedahl]

On 12/02/2014 12:30 PM, Junio C Hamano wrote:
> Duy Nguyen <pclouds@gmail.com> writes:
>
>> FWIW git-branch usually can show the original branch of detached head
>> (must not always). I don't think we have a plumbing equivalent for it
>> though. People can "tail -1 $GIT_DIR/logs/HEAD| sed .." but that seems
>> hacky.
> @{-1}, i.e. "the last branch I checked out"?
>
>> I do like "read-only" ref concept where we can keep ref name
>> (especially tags) in HEAD until the next commit. But it didn't go
>> anywhere
> Remind me.  That sounds somewhat interesting.
>
>
I think these ideas support solutions more complicated than the 
"problem" trying to be solved. Consider a use case: multiple algorithms, 
each a different branch in one repository, any of which can be used to 
analyze the same kinds of data. We also have multiple data sets, each a 
separate branch in a other repository. For development / test / analysis 
it is necessary to have multiple checked out pairs (algorithm + data) on 
the same machine to allow comparison / debugging in place of different 
combinations. Assume one algorithm, multiple data sets are checked out 
and being worked on.

With new-workdir, or Duy's approach with --ignore-other-checkouts, all 
are checked out normally in git, git-branch, git-status, git log all 
work normally. If a change needs to be made that affects the branch in 
more than one checked out repository, once done the other copies are out 
of date. It does not matter which instance is modified, once committed 
the change is already visible in all others, and "git reset --hard" in 
all the others completes the process. This is not difficult to 
understand, requires no new code, no special methods.

Consider the alternatives:
a) Use separate complete repositories + work trees: now the new branch 
needs to be broadcast to all using fetch or pull, and as the change 
might have been an amend, fetch + reset --hard may be required. This is 
not "simpler" to implement in practice, nor do I find it easier to 
explain. Note also that if using push, it is possible to force push into 
the current branch of the other copies, with receive.denyCurrentBranch = 
false, resulting in exactly the same situation as above using 
new-workdir (checked out code not matching the ref).

b) Use Duy's approach without --ignore-other-checkouts. First, you have 
to find the copy that is not on a detached HEAD, detach the HEAD their, 
then go back to the copy where the problem is found, attach the HEAD in 
that one, and make the change. Then go back and do git reset --hard 
$branch in the others.

I just don't see how these alternatives are in the end any simpler to 
use or explain.


Mark

Re: [PATCH 24/34] checkout: reject if the branch is already checked out elsewhere

[Duy Nguyen]

On Wed, Dec 3, 2014 at 12:30 AM, Junio C Hamano <gitster@pobox.com> wrote:
>> I do like "read-only" ref concept where we can keep ref name
>> (especially tags) in HEAD until the next commit. But it didn't go
>> anywhere
>
> Remind me.  That sounds somewhat interesting.

Couldn't find anything in my mail archive. But the idea is simple:

 - we delay detaching HEAD until we need to update the associated ref
at commit/reset time
 - currently refs/tags/* are read-only. we generalize it to allow this
'read-only' attribute on some refs/heads/* as well. Because we can't
really add attributes to refs, config var could be used.
-- 
Duy

Re: [PATCH 24/34] checkout: reject if the branch is already checked out elsewhere

[Junio C Hamano]

Duy Nguyen <pclouds@gmail.com> writes:

> On Wed, Dec 3, 2014 at 12:30 AM, Junio C Hamano <gitster@pobox.com> wrote:
>>> I do like "read-only" ref concept where we can keep ref name
>>> (especially tags) in HEAD until the next commit. But it didn't go
>>> anywhere
>>
>> Remind me.  That sounds somewhat interesting.
>
> Couldn't find anything in my mail archive. But the idea is simple:
>
>  - we delay detaching HEAD until we need to update the associated ref
> at commit/reset time
>  - currently refs/tags/* are read-only. we generalize it to allow this
> 'read-only' attribute on some refs/heads/* as well. Because we can't
> really add attributes to refs, config var could be used.

It could be some annotation in HEAD instead, e.g.

    $ cat .git/HEAD
    ref: refs/heads/frotz
    options: read-only
    $ exit

and it may make more sense as this read-only-ness is closely tied to
the state of HEAD, i.e. whatever operation that manipulates the
HEAD, it needs to be very much aware of the read-only-ness, and it
is much less likely to go out of sync, compared to a solution where
you store this bit to anywhere else, e.g. config.