[PATCH v2 13/21] setup: support $GIT_SUPER_DIR as well as super .git files

["Nguyễn Thái Ngọc Duy" <pclouds@gmail.com>]

The same rules for git repo setup apply except:

- detect super .git files, set $GIT_SUPER_DIR accordingly

- if $GIT_SUPER_DIR is set (or specified by super .git files), look
  for non-worktree stuff in this directory instead of $GIT_DIR. This
  mostly affects is_git_directory() and check_repository_format()

- the worktree setting precedence goes from lower to higher:
  core.worktree, GIT_SUPER_DIR then GIT_WORK_TREE

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
---
 Documentation/config.txt               |  3 +-
 Documentation/gitrepository-layout.txt | 10 ++++
 builtin/rev-parse.c                    |  6 +++
 cache.h                                |  1 +
 environment.c                          | 11 +++++
 setup.c                                | 89 ++++++++++++++++++++++++----------
 t/t1501-worktree.sh                    | 52 ++++++++++++++++++++
 t/t1510-repo-setup.sh                  |  1 +
 trace.c                                |  1 +
 9 files changed, 147 insertions(+), 27 deletions(-)

diff --git a/Documentation/config.txt b/Documentation/config.txt
index a405806..df19aa8 100644
--- a/Documentation/config.txt
+++ b/Documentation/config.txt
@@ -381,7 +381,8 @@ false), while all other repositories are assumed to be bare (bare
 
 core.worktree::
 	Set the path to the root of the working tree.
-	This can be overridden by the GIT_WORK_TREE environment
+	This can be overridden by the GIT_WORK_TREE
+	or GIT_SUPER_DIR environment
 	variable and the '--work-tree' command line option.
 	The value can be an absolute path or relative to the path to
 	the .git directory, which is either specified by --git-dir
diff --git a/Documentation/gitrepository-layout.txt b/Documentation/gitrepository-layout.txt
index aa03882..7ce31d4 100644
--- a/Documentation/gitrepository-layout.txt
+++ b/Documentation/gitrepository-layout.txt
@@ -29,6 +29,10 @@ containing superproject to `git checkout` a branch that does not
 have the submodule.  The `checkout` has to remove the entire
 submodule working tree, without losing the submodule repository.
 
+If the text file contains `gitsuper: <path>`, this is a "working
+directory only" repository, attached to another repository and share
+everything with the attached repository except HEAD and the index.
+
 These things may exist in a Git repository.
 
 objects::
@@ -214,6 +218,12 @@ shallow::
 modules::
 	Contains the git-repositories of the submodules.
 
+repos/<id>::
+	If a repository's .git is a file contains two lines `gitsuper:
+	<path>` and `repo: <id>`. The directory `<path>/repos/<id>`
+	contains the real non-shared part of .git directory of the
+	repository in question (e.g. HEAD or index).
+
 SEE ALSO
 --------
 linkgit:git-init[1],
diff --git a/builtin/rev-parse.c b/builtin/rev-parse.c
index 1d9ecaf..f5f766a 100644
--- a/builtin/rev-parse.c
+++ b/builtin/rev-parse.c
@@ -725,6 +725,12 @@ int cmd_rev_parse(int argc, const char **argv, const char *prefix)
 				printf("%s%s.git\n", cwd, len && cwd[len-1] != '/' ? "/" : "");
 				continue;
 			}
+			if (!strcmp(arg, "--git-super-dir")) {
+				const char *gitdir = getenv(GIT_SUPER_DIR_ENVIRONMENT);
+				if (gitdir)
+					puts(gitdir);
+				continue;
+			}
 			if (!strcmp(arg, "--resolve-git-dir")) {
 				const char *gitdir = resolve_gitdir(argv[i+1]);
 				if (!gitdir)
diff --git a/cache.h b/cache.h
index f85ee70..4c09223 100644
--- a/cache.h
+++ b/cache.h
@@ -406,6 +406,7 @@ 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 set_git_dir_super(const char *path, const char *super);
 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 cbfa879..5cbbe11 100644
--- a/environment.c
+++ b/environment.c
@@ -284,6 +284,17 @@ int set_git_dir(const char *path)
 	return 0;
 }
 
+int set_git_dir_super(const char *path, const char *super)
+{
+	if (super && super != path &&
+	    setenv(GIT_SUPER_DIR_ENVIRONMENT, super, 1))
+		return error("Could not set GIT_SUPER_DIR to '%s'", super);
+	if (setenv(GIT_DIR_ENVIRONMENT, path, 1))
+		return error("Could not set GIT_DIR to '%s'", path);
+	setup_git_env();
+	return 0;
+}
+
 const char *get_log_output_encoding(void)
 {
 	return git_log_output_encoding ? git_log_output_encoding
diff --git a/setup.c b/setup.c
index 397eecc..7ccb1f8 100644
--- a/setup.c
+++ b/setup.c
@@ -243,7 +243,8 @@ int is_inside_work_tree(void)
 
 void setup_work_tree(void)
 {
-	const char *work_tree, *git_dir;
+	const char *work_tree, *git_dir, *git_super_dir;
+	char *super_new = NULL, *super_relative = NULL;
 	static int initialized = 0;
 
 	if (initialized)
@@ -252,6 +253,9 @@ void setup_work_tree(void)
 	git_dir = get_git_dir();
 	if (!is_absolute_path(git_dir))
 		git_dir = real_path(get_git_dir());
+	git_super_dir = get_git_super_dir();
+	if (git_super_dir && !is_absolute_path(git_super_dir))
+		git_super_dir = super_new = xstrdup(real_path(get_git_super_dir()));
 	if (!work_tree || chdir(work_tree))
 		die("This operation must be run in a work tree");
 
@@ -262,8 +266,16 @@ void setup_work_tree(void)
 	if (getenv(GIT_WORK_TREE_ENVIRONMENT))
 		setenv(GIT_WORK_TREE_ENVIRONMENT, ".", 1);
 
-	set_git_dir(remove_leading_path(git_dir, work_tree));
+	if (git_super_dir) {
+		super_relative = xstrdup(remove_leading_path(git_super_dir, work_tree));
+		git_super_dir = super_relative;
+	}
+
+	set_git_dir_super(remove_leading_path(git_dir, work_tree),
+			  git_super_dir);
 	initialized = 1;
+	free(super_new);
+	free(super_relative);
 }
 
 static int check_repository_format_gently(const char *gitdir, int *nongit_ok)
@@ -386,24 +398,30 @@ const char *read_gitfile(const char *path)
 
 
 static const char *setup_explicit_git_dir(const char *gitdirenv,
+					  const char *super,
 					  char *cwd, int len,
 					  int *nongit_ok)
 {
 	const char *work_tree_env = getenv(GIT_WORK_TREE_ENVIRONMENT);
 	const char *worktree;
-	char *gitfile;
+	char *gitfile, *super_new = NULL;
 	int offset;
 
 	if (PATH_MAX - 40 < strlen(gitdirenv))
 		die("'$%s' too big", GIT_DIR_ENVIRONMENT);
 
-	gitfile = (char*)read_gitfile(gitdirenv);
+	if (super)
+		gitfile = (char*)read_gitfile(gitdirenv);
+	else {
+		gitfile = (char*)read_gitfile_super(gitdirenv, &super_new);
+		super = super_new;
+	}
 	if (gitfile) {
 		gitfile = xstrdup(gitfile);
 		gitdirenv = gitfile;
 	}
 
-	if (!is_git_directory(gitdirenv)) {
+	if (!is_git_directory_super(gitdirenv, super)) {
 		if (nongit_ok) {
 			*nongit_ok = 1;
 			goto done_null;
@@ -411,7 +429,7 @@ static const char *setup_explicit_git_dir(const char *gitdirenv,
 		die("Not a git repository: '%s'", gitdirenv);
 	}
 
-	if (check_repository_format_gently(gitdirenv, nongit_ok))
+	if (check_repository_format_gently(super ? super : gitdirenv, nongit_ok))
 		goto done_null;
 
 	/* #3, #7, #11, #15, #19, #23, #27, #31 (see t1510) */
@@ -422,10 +440,10 @@ static const char *setup_explicit_git_dir(const char *gitdirenv,
 			die("core.bare and core.worktree do not make sense");
 
 		/* #18, #26 */
-		set_git_dir(gitdirenv);
+		set_git_dir_super(gitdirenv, super);
 		goto done_null;
 	}
-	else if (git_work_tree_cfg) { /* #6, #14 */
+	else if (git_work_tree_cfg && !super) { /* #6, #14 */
 		if (is_absolute_path(git_work_tree_cfg))
 			set_git_work_tree(git_work_tree_cfg);
 		else {
@@ -443,7 +461,7 @@ static const char *setup_explicit_git_dir(const char *gitdirenv,
 	}
 	else if (!git_env_bool(GIT_IMPLICIT_WORK_TREE_ENVIRONMENT, 1)) {
 		/* #16d */
-		set_git_dir(gitdirenv);
+		set_git_dir_super(gitdirenv, super);
 		goto done_null;
 	}
 	else /* #2, #10 */
@@ -454,43 +472,47 @@ static const char *setup_explicit_git_dir(const char *gitdirenv,
 
 	/* both get_git_work_tree() and cwd are already normalized */
 	if (!strcmp(cwd, worktree)) { /* cwd == worktree */
-		set_git_dir(gitdirenv);
+		set_git_dir_super(gitdirenv, super);
 		goto done_null;
 	}
 
 	offset = dir_inside_of(cwd, worktree);
 	if (offset >= 0) {	/* cwd inside worktree? */
-		set_git_dir(real_path(gitdirenv));
+		set_git_dir_super(real_path(gitdirenv), super);
 		if (chdir(worktree))
 			die_errno("Could not chdir to '%s'", worktree);
 		cwd[len++] = '/';
 		cwd[len] = '\0';
 		free(gitfile);
+		free(super_new);
 		return cwd + offset;
 	}
 
 	/* cwd outside worktree */
-	set_git_dir(gitdirenv);
+	set_git_dir_super(gitdirenv, super);
 
 done_null:
 	free(gitfile);
+	free(super_new);
 	return NULL;
 }
 
 static const char *setup_discovered_git_dir(const char *gitdir,
+					    const char *super,
 					    char *cwd, int offset, int len,
 					    int *nongit_ok)
 {
-	if (check_repository_format_gently(gitdir, nongit_ok))
+	if (check_repository_format_gently(super ? super : gitdir, nongit_ok))
 		return NULL;
 
 	/* --work-tree is set without --git-dir; use discovered one */
-	if (getenv(GIT_WORK_TREE_ENVIRONMENT) || git_work_tree_cfg) {
+	if (getenv(GIT_WORK_TREE_ENVIRONMENT) ||
+	    (git_work_tree_cfg && !super)) {
 		if (offset != len && !is_absolute_path(gitdir))
 			gitdir = xstrdup(real_path(gitdir));
 		if (chdir(cwd))
 			die_errno("Could not come back to cwd");
-		return setup_explicit_git_dir(gitdir, cwd, len, nongit_ok);
+		return setup_explicit_git_dir(gitdir, super, cwd, len, nongit_ok);
 	}
 
 	/* #16.2, #17.2, #20.2, #21.2, #24, #25, #28, #29 (see t1510) */
@@ -503,8 +525,8 @@ static const char *setup_discovered_git_dir(const char *gitdir,
 
 	/* #0, #1, #5, #8, #9, #12, #13 */
 	set_git_work_tree(".");
-	if (strcmp(gitdir, DEFAULT_GIT_DIR_ENVIRONMENT))
-		set_git_dir(gitdir);
+	if (strcmp(gitdir, DEFAULT_GIT_DIR_ENVIRONMENT) || super)
+		set_git_dir_super(gitdir, super);
 	inside_git_dir = 0;
 	inside_work_tree = 1;
 	if (offset == len)
@@ -534,7 +556,7 @@ static const char *setup_bare_git_dir(char *cwd, int offset, int len, int *nongi
 		gitdir = offset == len ? "." : xmemdupz(cwd, offset);
 		if (chdir(cwd))
 			die_errno("Could not come back to cwd");
-		return setup_explicit_git_dir(gitdir, cwd, len, nongit_ok);
+		return setup_explicit_git_dir(gitdir, NULL, cwd, len, nongit_ok);
 	}
 
 	inside_git_dir = 1;
@@ -613,8 +635,8 @@ static const char *setup_git_directory_gently_1(int *nongit_ok)
 	const char *env_ceiling_dirs = getenv(CEILING_DIRECTORIES_ENVIRONMENT);
 	struct string_list ceiling_dirs = STRING_LIST_INIT_DUP;
 	static char cwd[PATH_MAX + 1];
-	const char *gitdirenv, *ret;
-	char *gitfile;
+	const char *gitdirenv, *ret, *super;
+	char *gitfile, *super_new = NULL;
 	int len, offset, offset_parent, ceil_offset = -1;
 	dev_t current_device = 0;
 	int one_filesystem = 1;
@@ -637,8 +659,10 @@ static const char *setup_git_directory_gently_1(int *nongit_ok)
 	 * validation.
 	 */
 	gitdirenv = getenv(GIT_DIR_ENVIRONMENT);
+	super = getenv(GIT_SUPER_DIR_ENVIRONMENT);
 	if (gitdirenv)
-		return setup_explicit_git_dir(gitdirenv, cwd, len, nongit_ok);
+		return setup_explicit_git_dir(gitdirenv, super,
+					      cwd, len, nongit_ok);
 
 	if (env_ceiling_dirs) {
 		int empty_entry_found = 0;
@@ -668,25 +692,38 @@ static const char *setup_git_directory_gently_1(int *nongit_ok)
 	if (one_filesystem)
 		current_device = get_device_or_die(".", NULL, 0);
 	for (;;) {
-		gitfile = (char*)read_gitfile(DEFAULT_GIT_DIR_ENVIRONMENT);
+		if (super)
+			gitfile = (char*)read_gitfile(DEFAULT_GIT_DIR_ENVIRONMENT);
+		else {
+			gitfile = (char*)read_gitfile_super(DEFAULT_GIT_DIR_ENVIRONMENT,
+							    &super_new);
+			super = super_new;
+		}
 		if (gitfile)
 			gitdirenv = gitfile = xstrdup(gitfile);
 		else {
-			if (is_git_directory(DEFAULT_GIT_DIR_ENVIRONMENT))
+			if (is_git_directory_super(DEFAULT_GIT_DIR_ENVIRONMENT, super))
 				gitdirenv = DEFAULT_GIT_DIR_ENVIRONMENT;
 		}
 
 		if (gitdirenv) {
-			ret = setup_discovered_git_dir(gitdirenv,
+			ret = setup_discovered_git_dir(gitdirenv, super,
 						       cwd, offset, len,
 						       nongit_ok);
 			free(gitfile);
+			free(super_new);
 			return ret;
 		}
 		free(gitfile);
 
-		if (is_git_directory("."))
-			return setup_bare_git_dir(cwd, offset, len, nongit_ok);
+		if (is_git_directory(".")) {
+			ret = setup_bare_git_dir(cwd, offset, len, nongit_ok);
+			free(super_new);
+			return ret;
+		}
+
+		free(super_new);
+		super_new = NULL;
 
 		offset_parent = offset;
 		while (--offset_parent > ceil_offset && cwd[offset_parent] != '/');
diff --git a/t/t1501-worktree.sh b/t/t1501-worktree.sh
index 8f36aa9..dcd8d16 100755
--- a/t/t1501-worktree.sh
+++ b/t/t1501-worktree.sh
@@ -346,4 +346,56 @@ test_expect_success 'relative $GIT_WORK_TREE and git subprocesses' '
 	test_cmp expected actual
 '
 
+test_expect_success 'Split repo setup' '
+	mkdir work &&
+	mkdir -p repo.git/repos/foo &&
+	cp repo.git/HEAD repo.git/index repo.git/repos/foo
+'
+
+test_expect_success 'GIT_SUPER_DIR set' '
+	unset GIT_WORK_TREE GIT_DIR GIT_CONFIG &&
+	GIT_SUPER_DIR=repo.git GIT_DIR=repo.git/repos/foo git rev-parse --git-super-dir >actual &&
+	echo repo.git >expect &&
+	test_cmp expect actual
+'
+
+test_expect_success 'GIT_DIR set (1)' '
+	(
+		cat <<EOF >gitfile &&
+gitsuper: repo.git
+gitdir: foo
+EOF
+		cd work &&
+		GIT_DIR=../gitfile git rev-parse --git-super-dir >actual &&
+		echo ../repo.git >expect &&
+		test_cmp expect actual
+	)
+'
+
+test_expect_success 'GIT_DIR set (2)' '
+	(
+		cat <<EOF >gitfile &&
+gitsuper: $TRASH_DIRECTORY/repo.git
+gitdir: foo
+EOF
+		cd work &&
+		GIT_DIR=../gitfile git rev-parse --git-super-dir >actual &&
+		echo "$TRASH_DIRECTORY"/repo.git >expect &&
+		test_cmp expect actual
+	)
+'
+
+test_expect_success 'Auto discovery' '
+	(
+		cat <<EOF >.git &&
+gitsuper: repo.git
+gitdir: foo
+EOF
+		cd work &&
+		git rev-parse --git-super-dir >actual &&
+		echo repo.git >expect &&
+		test_cmp expect actual
+	)
+'
+
 test_done
diff --git a/t/t1510-repo-setup.sh b/t/t1510-repo-setup.sh
index cf2ee78..713f4d7 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_super_dir: (null)
 	setup: worktree: $3
 	setup: cwd: $4
 	setup: prefix: $5
diff --git a/trace.c b/trace.c
index 3d744d1..53d800b 100644
--- a/trace.c
+++ b/trace.c
@@ -173,6 +173,7 @@ 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_super_dir: %s\n", quote_crnl(get_git_super_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));
-- 
1.8.5.1.77.g42c48fa