[PATCH 3/3] init: do not set core.worktree more often than necessary

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

When "git init" is called with GIT_WORK_TREE environment set, we want to
keep this worktree's location in core.worktree so the user does not have
to set the environment again and again. See ef6f0af (git-init: set
core.worktree if GIT_WORK_TREE is specified - 2007-07-04)

We detect that by this logic (in needs_work_tree_config): normally
worktree's top dir would contains ".git" directory, if this is not true,
worktree is probably set to elsewhere by the user.

Unfortunately when it calls get_git_dir() it does not take ".git" files
into account. When we find a .git file, we immediately follow the file
until we find the real ".git" directory. The location of this first
".git" file is lost.

The .git file would satisfy the logic above and not create
core.worktree (correct). But because the final .git's location is used,
needs_work_tree_config() is misled and creates core.worktree anyway.

This would not be a huge deal normally. But if this happens in a
multiple worktree setup it becomes a real problem because up until now,
core.worktree will be applied to the main worktree only. If you
accidentally do "git init" from a linked worktree, you set
core.worktree (for the main repo) pointing to the _linked_ worktree.
After that point, may you live in interesting times.

Record the .git file location and use it here.

Noticed-by: Max Nordlund <max.nordlund@sqore.com>
Helped-by: Michael J Gruber <git@drmicha.warpmail.net>
Signed-off-by: Nguyễn Thái Ngọc Duy <pclouds@gmail.com>
---
 builtin/init-db.c |  2 +-
 cache.h           |  1 +
 environment.c     | 16 +++++++++++++++-
 t/t0001-init.sh   |  2 ++
 4 files changed, 19 insertions(+), 2 deletions(-)

diff --git a/builtin/init-db.c b/builtin/init-db.c
index 6d9552e..36255f2 100644
--- a/builtin/init-db.c
+++ b/builtin/init-db.c
@@ -254,7 +254,7 @@ static int create_default_files(const char *template_path)
 		/* allow template config file to override the default */
 		if (log_all_ref_updates == -1)
 			git_config_set("core.logallrefupdates", "true");
-		if (needs_work_tree_config(get_git_dir(), work_tree))
+		if (needs_work_tree_config(get_first_git_dir(), work_tree))
 			git_config_set("core.worktree", work_tree);
 	}
 
diff --git a/cache.h b/cache.h
index b780a91..e6c05f8 100644
--- a/cache.h
+++ b/cache.h
@@ -460,6 +460,7 @@ 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 const char *get_first_git_dir(void);
 extern char *get_object_directory(void);
 extern char *get_index_file(void);
 extern char *get_graft_file(void);
diff --git a/environment.c b/environment.c
index ca72464..8cfb8f3 100644
--- a/environment.c
+++ b/environment.c
@@ -100,7 +100,7 @@ static char *work_tree;
 static const char *namespace;
 static size_t namespace_len;
 
-static const char *git_dir, *git_common_dir;
+static const char *git_dir, *git_common_dir, *first_git_dir;
 static char *git_object_dir, *git_index_file, *git_graft_file;
 int git_db_env, git_index_env, git_graft_env, git_common_dir_env;
 
@@ -168,6 +168,8 @@ static void setup_git_env(void)
 	if (!git_dir)
 		git_dir = DEFAULT_GIT_DIR_ENVIRONMENT;
 	gitfile = read_gitfile(git_dir);
+	if (gitfile && !first_git_dir)
+		first_git_dir = xstrdup(git_dir);
 	git_dir = xstrdup(gitfile ? gitfile : git_dir);
 	if (get_common_dir(&sb, git_dir))
 		git_common_dir_env = 1;
@@ -203,6 +205,18 @@ const char *get_git_dir(void)
 	return git_dir;
 }
 
+/*
+ * Return the first ".git" that we have encountered.
+ * FIXME this function for not entirely correct because
+ * setup_git_directory() and enter_repo() do not update first_git_dir
+ * when they follow .git files. The function in its current state is
+ * only suitable for "git init".
+ */
+const char *get_first_git_dir(void)
+{
+	return first_git_dir ? first_git_dir : git_dir;
+}
+
 const char *get_git_common_dir(void)
 {
 	return git_common_dir;
diff --git a/t/t0001-init.sh b/t/t0001-init.sh
index 393c940..d59669a 100755
--- a/t/t0001-init.sh
+++ b/t/t0001-init.sh
@@ -393,9 +393,11 @@ test_expect_success 're-init from a linked worktree' '
 		test_commit first &&
 		git worktree add ../linked-worktree &&
 		mv .git/info/exclude expected-exclude &&
+		cp .git/config expected-config &&
 		find .git/worktrees -print | sort >expected &&
 		git -C ../linked-worktree init &&
 		test_cmp expected-exclude .git/info/exclude &&
+		test_cmp expected-config .git/config &&
 		find .git/worktrees -print | sort >actual &&
 		test_cmp expected actual
 	)
-- 
2.8.2.524.g6ff3d78