path: refactor repo_worktree_path() family of functions

As explained in an earlier commit, we're refactoring path-related
functions to provide a consistent interface for computing paths into the
commondir, gitdir and worktree. Refactor the "worktree" family of
functions accordingly.

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

path.c

@@ -519,9 +519,6 @@ char *repo_worktree_path(const struct repository *repo, const char *fmt, ...)
 	struct strbuf path = STRBUF_INIT;
 	va_list args;
 
-	if (!repo->worktree)
-		return NULL;
-
 	va_start(args, fmt);
 	do_worktree_path(repo, &path, fmt, args);
 	va_end(args);
@@ -529,18 +526,37 @@ char *repo_worktree_path(const struct repository *repo, const char *fmt, ...)
 	return strbuf_detach(&path, NULL);
 }
 
-void strbuf_repo_worktree_path(struct strbuf *sb,
+const char *repo_worktree_path_append(const struct repository *repo,
-			       const struct repository *repo,
+				      struct strbuf *sb,
-			       const char *fmt, ...)
+				      const char *fmt, ...)
 {
 	va_list args;
 
 	if (!repo->worktree)
-		return;
+		return NULL;
 
 	va_start(args, fmt);
 	do_worktree_path(repo, sb, fmt, args);
 	va_end(args);
+
+	return sb->buf;
+}
+
+const char *repo_worktree_path_replace(const struct repository *repo,
+				       struct strbuf *sb,
+				       const char *fmt, ...)
+{
+	va_list args;
+
+	strbuf_reset(sb);
+	if (!repo->worktree)
+		return NULL;
+
+	va_start(args, fmt);
+	do_worktree_path(repo, sb, fmt, args);
+	va_end(args);
+
+	return sb->buf;
 }
 
 /* Returns 0 on success, negative on failure. */

path.h

@@ -75,24 +75,22 @@ const char *worktree_git_path(struct repository *r,
 	__attribute__((format (printf, 3, 4)));
 
 /*
- * Return a path into the worktree of repository `repo`.
+ * The `repo_worktree_path` family of functions will construct a path into a
+ * repository's worktree.
  *
- * If the repository doesn't have a worktree NULL is returned.
+ * Returns a `NULL` pointer in case the repository has no worktree.
  */
 char *repo_worktree_path(const struct repository *repo,
 				const char *fmt, ...)
 	__attribute__((format (printf, 2, 3)));
-
+const char *repo_worktree_path_append(const struct repository *repo,
-/*
+				      struct strbuf *sb,
- * Construct a path into the worktree of repository `repo` and append it
- * to the provided buffer `sb`.
- *
- * If the repository doesn't have a worktree nothing will be appended to `sb`.
- */
-void strbuf_repo_worktree_path(struct strbuf *sb,
-				      const struct repository *repo,
 				      const char *fmt, ...)
 	__attribute__((format (printf, 3, 4)));
+const char *repo_worktree_path_replace(const struct repository *repo,
+				       struct strbuf *sb,
+				       const char *fmt, ...)
+	__attribute__((format (printf, 3, 4)));
 
 /*
  * Return a path into a submodule's git directory located at `path`.  `path`

repository.c

@@ -312,8 +312,8 @@ int repo_submodule_init(struct repository *subrepo,
 	struct strbuf worktree = STRBUF_INIT;
 	int ret = 0;
 
-	strbuf_repo_worktree_path(&gitdir, superproject, "%s/.git", path);
+	repo_worktree_path_append(superproject, &gitdir, "%s/.git", path);
-	strbuf_repo_worktree_path(&worktree, superproject, "%s", path);
+	repo_worktree_path_append(superproject, &worktree, "%s", path);
 
 	if (repo_init(subrepo, gitdir.buf, worktree.buf)) {
 		/*