stash: optimize `get_untracked_files()` and `check_changes()`

This commits introduces a optimization by avoiding calling the
same functions again. For example, `git stash push -u`
would call at some points the following functions:

 * `check_changes()` (inside `do_push_stash()`)
 * `do_create_stash()`, which calls: `check_changes()` and
`get_untracked_files()`

Note that `check_changes()` also calls `get_untracked_files()`.
So, `check_changes()` is called 2 times and `get_untracked_files()`
3 times.

The old function `check_changes()` now consists of two functions:
`get_untracked_files()` and `check_changes_tracked_files()`.

These are the call chains for `push` and `create`:

 * `push_stash()` -> `do_push_stash()` -> `do_create_stash()`

 * `create_stash()` -> `do_create_stash()`

To prevent calling the same functions over and over again,
`check_changes()` inside `do_create_stash()` is now placed
in the caller functions (`create_stash()` and `do_push_stash()`).
This way `check_changes()` and `get_untracked files()` are called
only one time.

Signed-off-by: Paul-Sebastian Ungureanu <ungureanupaulsebastian@gmail.com>
Signed-off-by: Thomas Gummerer <t.gummerer@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/stash--helper.c

@@ -879,18 +879,17 @@ static int get_untracked_files(struct pathspec ps, int include_untracked,
 }
 
 /*
- * The return value of `check_changes()` can be:
+ * The return value of `check_changes_tracked_files()` can be:
  *
  * < 0 if there was an error
  * = 0 if there are no changes.
  * > 0 if there are changes.
  */
-static int check_changes(struct pathspec ps, int include_untracked)
+static int check_changes_tracked_files(struct pathspec ps)
 {
 	int result;
 	struct rev_info rev;
 	struct object_id dummy;
-	struct strbuf out = STRBUF_INIT;
 
 	/* No initial commit. */
 	if (get_oid("HEAD", &dummy))
@@ -918,16 +917,27 @@ static int check_changes(struct pathspec ps, int include_untracked)
 	if (diff_result_code(&rev.diffopt, result))
 		return 1;
 
-	if (include_untracked && get_untracked_files(ps, include_untracked,
-						     &out)) {
-		strbuf_release(&out);
-		return 1;
-	}
-
-	strbuf_release(&out);
 	return 0;
 }
 
+/*
+ * The function will fill `untracked_files` with the names of untracked files
+ * It will return 1 if there were any changes and 0 if there were not.
+ */
+static int check_changes(struct pathspec ps, int include_untracked,
+			 struct strbuf *untracked_files)
+{
+	int ret = 0;
+	if (check_changes_tracked_files(ps))
+		ret = 1;
+
+	if (include_untracked && get_untracked_files(ps, include_untracked,
+						     untracked_files))
+		ret = 1;
+
+	return ret;
+}
+
 static int save_untracked_files(struct stash_info *info, struct strbuf *msg,
 				struct strbuf files)
 {
@@ -1137,7 +1147,7 @@ static int do_create_stash(struct pathspec ps, struct strbuf *stash_msg_buf,
 		head_commit = lookup_commit(the_repository, &info->b_commit);
 	}
 
-	if (!check_changes(ps, include_untracked)) {
+	if (!check_changes(ps, include_untracked, &untracked_files)) {
 		ret = 1;
 		goto done;
 	}
@@ -1162,8 +1172,7 @@ static int do_create_stash(struct pathspec ps, struct strbuf *stash_msg_buf,
 		goto done;
 	}
 
-	if (include_untracked && get_untracked_files(ps, include_untracked,
-						     &untracked_files)) {
+	if (include_untracked) {
 		if (save_untracked_files(info, &msg, untracked_files)) {
 			if (!quiet)
 				fprintf_ln(stderr, _("Cannot save "
@@ -1248,6 +1257,9 @@ static int create_stash(int argc, const char **argv, const char *prefix)
 			     0);
 
 	memset(&ps, 0, sizeof(ps));
+	if (!check_changes_tracked_files(ps))
+		return 0;
+
 	strbuf_addstr(&stash_msg_buf, stash_msg);
 	ret = do_create_stash(ps, &stash_msg_buf, include_untracked, 0, &info,
 			      NULL, 0);
@@ -1255,12 +1267,7 @@ static int create_stash(int argc, const char **argv, const char *prefix)
 		printf_ln("%s", oid_to_hex(&info.w_commit));
 
 	strbuf_release(&stash_msg_buf);
-
-	/*
-	 * ret can be 1 if there were no changes. In this case, we should
-	 * not error out.
-	 */
-	return ret < 0;
+	return ret;
 }
 
 static int do_push_stash(struct pathspec ps, const char *stash_msg, int quiet,
@@ -1270,6 +1277,7 @@ static int do_push_stash(struct pathspec ps, const char *stash_msg, int quiet,
 	struct stash_info info;
 	struct strbuf patch = STRBUF_INIT;
 	struct strbuf stash_msg_buf = STRBUF_INIT;
+	struct strbuf untracked_files = STRBUF_INIT;
 
 	if (patch_mode && keep_index == -1)
 		keep_index = 1;
@@ -1304,7 +1312,7 @@ static int do_push_stash(struct pathspec ps, const char *stash_msg, int quiet,
 		goto done;
 	}
 
-	if (!check_changes(ps, include_untracked)) {
+	if (!check_changes(ps, include_untracked, &untracked_files)) {
 		if (!quiet)
 			printf_ln(_("No local changes to save"));
 		goto done;