[PATCH 1/3] config.c: new config namespace worktree.* stored in $GIT_DIR/config.worktree

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

On the surface, worktree.* variables are just like any other
variables. You can read or modify them with `git config` command, or
config_* API. Underneath, worktree.* are always stored in
$GIT_DIR/config.worktree instead of $GIT_DIR/config (and never in
$HOME/.gitconfig or /etc/gitconfig)

The reason for this split is, as the name implies, for
worktree-specific configuration. When the same repo is attached to
more than one worktree, we can't use $GIT_DIR/config to store worktree
specific stuff because it's shared across worktrees.

With this, both git-new-workdir and nd/multiple-work-trees will work.
git-new-workdir creates a symlink to $GIT_DIR/config in the new
worktree, but not $GIT_DIR/config.worktree. That file will be created
new when worktree.* are written in the new worktree.
`git checkout --to` can remap the path $GIT_DIR/config.worktree to make
it worktree-specific.

Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
---
 Documentation/config.txt |  4 +++-
 builtin/config.c         |  8 ++++++++
 config.c                 | 38 ++++++++++++++++++++++++++++++++++++++
 t/t1300-repo-config.sh   | 31 +++++++++++++++++++++++++++++++
 4 files changed, 80 insertions(+), 1 deletion(-)

diff --git a/Documentation/config.txt b/Documentation/config.txt
index 04e2a71..26e4e07 100644
--- a/Documentation/config.txt
+++ b/Documentation/config.txt
@@ -2,11 +2,13 @@ CONFIGURATION FILE
 ------------------
 
 The Git configuration file contains a number of variables that affect
-the Git commands' behavior. The `.git/config` file in each repository
+the Git commands' behavior. The `.git/config` and `.git/config.worktree`
+files in each repository
 is used to store the configuration for that repository, and
 `$HOME/.gitconfig` is used to store a per-user configuration as
 fallback values for the `.git/config` file. The file `/etc/gitconfig`
 can be used to store a system-wide default configuration.
+worktree.* variables can only be contained in `.git/config.worktree`
 
 The configuration variables are used by both the Git plumbing
 and the porcelains. The variables are divided into sections, wherein
diff --git a/builtin/config.c b/builtin/config.c
index 15a7bea..d9333cd 100644
--- a/builtin/config.c
+++ b/builtin/config.c
@@ -552,6 +552,14 @@ int cmd_config(int argc, const char **argv, const char *prefix)
 			usage_with_options(builtin_config_usage, builtin_config_options);
 		}
 
+	/*
+	 * For set operations, --local could be either config or
+	 * config.worktree. Let config.c determine the path based on
+	 * config keys.
+	 */
+	if (use_local_config && actions != ACTION_LIST)
+		given_config_source.file = NULL;
+
 	if (actions == ACTION_LIST) {
 		check_argc(argc, 0, 0);
 		if (git_config_with_options(show_all_config, NULL,
diff --git a/config.c b/config.c
index 752e2e2..3d46192 100644
--- a/config.c
+++ b/config.c
@@ -12,6 +12,7 @@
 #include "quote.h"
 #include "hashmap.h"
 #include "string-list.h"
+#include "dir.h"
 
 struct config_source {
 	struct config_source *prev;
@@ -1177,6 +1178,15 @@ int git_config_system(void)
 	return !git_env_bool("GIT_CONFIG_NOSYSTEM", 0);
 }
 
+static int config_worktree_filter(const char *var, const char *value, void *data)
+{
+	struct config_include_data *inc = data;
+
+	if (!starts_with(var, "worktree."))
+		return error("$GIT_DIR/config.worktree can only contain worktree.*");
+	return inc->fn(var, value, inc->data);
+}
+
 int git_config_early(config_fn_t fn, void *data, const char *repo_config)
 {
 	int ret = 0, found = 0;
@@ -1202,8 +1212,19 @@ int git_config_early(config_fn_t fn, void *data, const char *repo_config)
 	}
 
 	if (repo_config && !access_or_die(repo_config, R_OK, 0)) {
+		char *wt_config;
 		ret += git_config_from_file(fn, repo_config, data);
 		found += 1;
+		wt_config = git_pathdup("config.worktree");
+		if (!access_or_die(wt_config, R_OK, 0)) {
+			struct config_include_data inc = CONFIG_INCLUDE_INIT;
+			inc.fn = fn;
+			inc.data = data;
+			ret += git_config_from_file(config_worktree_filter,
+						    wt_config, &inc);
+			found += 1;
+		}
+		free(wt_config);
 	}
 
 	switch (git_config_from_parameters(fn, data)) {
@@ -1942,6 +1963,23 @@ int git_config_set_multivar_in_file(const char *config_filename,
 
 	store.multi_replace = multi_replace;
 
+	if (starts_with(key, "worktree.")) {
+		if (!config_filename)
+			config_filename = filename_buf = git_pathdup("config.worktree");
+		/* cheap trick, but should work 90% of time */
+		else if (!ends_with(config_filename, ".worktree"))
+			die("worktree.* can only be stored in %s",
+			    git_path("config.worktree"));
+		else {
+			struct strbuf sb = STRBUF_INIT;
+			strbuf_addstr(&sb, real_path(config_filename));
+			if (strcmp_icase(sb.buf,
+					 real_path(git_path("config.worktree"))))
+				die("worktree.* can only be stored in %s",
+				    git_path("config.worktree"));
+			strbuf_release(&sb);
+		}
+	}
 	if (!config_filename)
 		config_filename = filename_buf = git_pathdup("config");
 
diff --git a/t/t1300-repo-config.sh b/t/t1300-repo-config.sh
index 938fc8b..58a5009 100755
--- a/t/t1300-repo-config.sh
+++ b/t/t1300-repo-config.sh
@@ -1179,4 +1179,35 @@ test_expect_success POSIXPERM,PERL 'preserves existing permissions' '
 	  "die q(badrename) if ((stat(q(.git/config)))[2] & 07777) != 0600"
 '
 
+test_expect_success 'setting worktree.foo goes to config.worktree' '
+	test_when_finished "rm .git/config.worktree" &&
+	git config worktree.foo bar &&
+	cat >expect <<\EOF &&
+[worktree]
+	foo = bar
+EOF
+	test_cmp expect .git/config.worktree &&
+	test "`git config worktree.foo`" = bar
+'
+
+test_expect_success 'setting --local worktree.foo goes to config.worktree' '
+	test_when_finished "rm .git/config.worktree" &&
+	git config --local worktree.fooo barr &&
+	cat >expect <<\EOF &&
+[worktree]
+	fooo = barr
+EOF
+	test_cmp expect .git/config.worktree &&
+	test "`git config worktree.fooo`" = barr
+'
+
+test_expect_success 'setting worktree.foo outside config.worktree' '
+	test_must_fail git config --global worktree.foo bar 2>err &&
+	grep config.worktree err &&
+	test_must_fail git config --system worktree.foo bar 2>err &&
+	grep config.worktree err &&
+	test_must_fail git config --file foo.worktree worktree.foo bar 2>err &&
+	grep config.worktree err
+'
+
 test_done
-- 
2.3.0.rc1.137.g477eb31