path: add repo_git_path and strbuf_repo_git_path

Introduce 'repo_git_path' and 'strbuf_repo_git_path' which take a
repository struct and constructs a path into the repository's git
directory.

Signed-off-by: Brandon Williams <bmwill@google.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

path.c

@@ -416,6 +416,27 @@ static void do_git_path(const struct repository *repo,
 	strbuf_cleanup_path(buf);
 }
 
+char *repo_git_path(const struct repository *repo,
+		    const char *fmt, ...)
+{
+	struct strbuf path = STRBUF_INIT;
+	va_list args;
+	va_start(args, fmt);
+	do_git_path(repo, NULL, &path, fmt, args);
+	va_end(args);
+	return strbuf_detach(&path, NULL);
+}
+
+void strbuf_repo_git_path(struct strbuf *sb,
+			  const struct repository *repo,
+			  const char *fmt, ...)
+{
+	va_list args;
+	va_start(args, fmt);
+	do_git_path(repo, NULL, sb, fmt, args);
+	va_end(args);
+}
+
 char *git_path_buf(struct strbuf *buf, const char *fmt, ...)
 {
 	va_list args;

path.h

@@ -35,6 +35,14 @@ extern char *mkpathdup(const char *fmt, ...)
 extern char *git_pathdup_submodule(const char *path, const char *fmt, ...)
 	__attribute__((format (printf, 2, 3)));
 
+extern char *repo_git_path(const struct repository *repo,
+			   const char *fmt, ...)
+	__attribute__((format (printf, 2, 3)));
+extern void strbuf_repo_git_path(struct strbuf *sb,
+				 const struct repository *repo,
+				 const char *fmt, ...)
+	__attribute__((format (printf, 3, 4)));
+
 extern void report_linked_checkout_garbage(void);
 
 /*