worktree: return allocated string from `get_worktree_git_dir()`

The `get_worktree_git_dir()` function returns a string constant that
does not need to be free'd by the caller. This string is computed for
three different cases:

  - If we don't have a worktree we return a path into the Git directory.
    The returned string is owned by `the_repository`, so there is no
    need for the caller to free it.

  - If we have a worktree, but no worktree ID then the caller requests
    the main worktree. In this case we return a path into the common
    directory, which again is owned by `the_repository` and thus does
    not need to be free'd.

  - In the third case, where we have an actual worktree, we compute the
    path relative to "$GIT_COMMON_DIR/worktrees/". This string does not
    need to be released either, even though `git_common_path()` ends up
    allocating memory. But this doesn't result in a memory leak either
    because we write into a buffer returned by `get_pathname()`, which
    returns one out of four static buffers.

We're about to drop `git_common_path()` in favor of `repo_common_path()`,
which doesn't use the same mechanism but instead returns an allocated
string owned by the caller. While we could adapt `get_worktree_git_dir()`
to also use `get_pathname()` and print the derived common path into that
buffer, the whole schema feels a lot like premature optimization in this
context. There are some callsites where we call `get_worktree_git_dir()`
in a loop that iterates through all worktrees. But none of these loops
seem to be even remotely in the hot path, so saving a single allocation
there does not feel worth it.

Refactor the function to instead consistently return an allocated path
so that we can start using `repo_common_path()` in a subsequent commit.

Signed-off-by: Patrick Steinhardt <ps@pks.im>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 6 insertions, 5 deletions

diff --git a/worktree.c b/worktree.c
index 8f4fc10c44..3b94535963 100644
--- a/worktree.c
+++ b/worktree.c
@@ -59,8 +59,9 @@ static void add_head_info(struct worktree *wt)
 static int is_current_worktree(struct worktree *wt)
 {
 	char *git_dir = absolute_pathdup(repo_get_git_dir(the_repository));
-	const char *wt_git_dir = get_worktree_git_dir(wt);
+	char *wt_git_dir = get_worktree_git_dir(wt);
 	int is_current = !fspathcmp(git_dir, absolute_path(wt_git_dir));
+	free(wt_git_dir);
 	free(git_dir);
 	return is_current;
 }
@@ -175,14 +176,14 @@ struct worktree **get_worktrees(void)
 	return get_worktrees_internal(0);
 }
 
-const char *get_worktree_git_dir(const struct worktree *wt)
+char *get_worktree_git_dir(const struct worktree *wt)
 {
 	if (!wt)
-		return repo_get_git_dir(the_repository);
+		return xstrdup(repo_get_git_dir(the_repository));
 	else if (!wt->id)
-		return repo_get_common_dir(the_repository);
+		return xstrdup(repo_get_common_dir(the_repository));
 	else
-		return git_common_path("worktrees/%s", wt->id);
+		return xstrdup(git_common_path("worktrees/%s", wt->id));
 }
 
 static struct worktree *find_worktree_by_suffix(struct worktree **list,