[RFC] status: show tracking branch even no difference

[Jiang Xin <worldhello.net@gmail.com>]

If the current branch has an upstream branch, and there are differences
between the current branch and its upstream, some commands (such as
"git status", "git status -bs", and "git checkout") will report their
relationship. E.g.

    $ git status
    # On branch master
    # Your branch is ahead of 'origin/master' by 1 commit.
    #   (use "git push" to publish your local commits)
    #
    ...

    $ git status -bs
    ## master...origin/master [ahead 1]
    ...

    $ git checkout master
    Already on 'master'
    Your branch is ahead of 'origin/master' by 1 commit.
      (use "git push" to publish your local commits)

But if there is no difference between the current branch and its
upstream, the relationship will not be reported, and it's hard to
tell whether the current branch has a tracking branch or not. And
what's worse, when the 'push.default' config variable is set to
`matching`, it's hard to tell whether current branch is pushed out
or not [1].

With this patch, "git status" will report relationship between current
branch and its upstream counterpart even if there is no difference.

    $ git status
    # On branch master
    # Your branch is identical to its tracking branch: 'origin/master'.
    #
    ...

    $ git status -bs
    ## master...origin/master
    ...

    $ git checkout master
    Already on 'master'
    Your branch is identical to its tracking branch: 'origin/master'.

[1]: http://thread.gmane.org/gmane.comp.version-control.git/198703

Signed-off-by: Jiang Xin <worldhello.net@gmail.com>
---
 remote.c    | 22 ++++++++++++++++------
 wt-status.c | 13 ++++++++++---
 2 files changed, 26 insertions(+), 9 deletions(-)

diff --git a/remote.c b/remote.c
index 2433467..8d6f278 100644
--- a/remote.c
+++ b/remote.c
@@ -1740,6 +1740,10 @@ int stat_tracking_info(struct branch *branch, int *num_ours, int *num_theirs)
 	const char *rev_argv[10], *base;
 	int rev_argc;
 
+	/* Set both num_theirs and num_ours as undetermined. */
+	*num_theirs = -1;
+	*num_ours = -1;
+
 	/*
 	 * Nothing to report unless we are marked to build on top of
 	 * somebody else.
@@ -1758,14 +1762,16 @@ int stat_tracking_info(struct branch *branch, int *num_ours, int *num_theirs)
 	theirs = lookup_commit_reference(sha1);
 	if (!theirs)
 		return 0;
+	*num_theirs = 0;
 
 	if (read_ref(branch->refname, sha1))
 		return 0;
 	ours = lookup_commit_reference(sha1);
 	if (!ours)
 		return 0;
+	*num_ours = 0;
 
-	/* are we the same? */
+	/* are we the same? both num_theirs and num_ours are set to 0. */
 	if (theirs == ours)
 		return 0;
 
@@ -1786,8 +1792,6 @@ int stat_tracking_info(struct branch *branch, int *num_ours, int *num_theirs)
 	prepare_revision_walk(&revs);
 
 	/* ... and count the commits on each side. */
-	*num_ours = 0;
-	*num_theirs = 0;
 	while (1) {
 		struct commit *c = get_revision(&revs);
 		if (!c)
@@ -1812,12 +1816,18 @@ int format_tracking_info(struct branch *branch, struct strbuf *sb)
 	int num_ours, num_theirs;
 	const char *base;
 
-	if (!stat_tracking_info(branch, &num_ours, &num_theirs))
-		return 0;
+	if (!stat_tracking_info(branch, &num_ours, &num_theirs)) {
+		if (num_ours || num_theirs)
+			return 0;
+	}
 
 	base = branch->merge[0]->dst;
 	base = shorten_unambiguous_ref(base, 0);
-	if (!num_theirs) {
+	if (!num_ours && !num_theirs) {
+		strbuf_addf(sb,
+			_("Your branch is identical to its tracking branch: '%s'.\n"),
+			base);
+	} else if (!num_theirs) {
 		strbuf_addf(sb,
 			Q_("Your branch is ahead of '%s' by %d commit.\n",
 			   "Your branch is ahead of '%s' by %d commits.\n",
diff --git a/wt-status.c b/wt-status.c
index ff4b324..56f3c19 100644
--- a/wt-status.c
+++ b/wt-status.c
@@ -1381,9 +1381,11 @@ static void wt_shortstatus_print_tracking(struct wt_status *s)
 	if (s->is_initial)
 		color_fprintf(s->fp, header_color, _("Initial commit on "));
 	if (!stat_tracking_info(branch, &num_ours, &num_theirs)) {
-		color_fprintf(s->fp, branch_color_local, "%s", branch_name);
-		fputc(s->null_termination ? '\0' : '\n', s->fp);
-		return;
+		if (num_ours || num_theirs) {
+			color_fprintf(s->fp, branch_color_local, "%s", branch_name);
+			fputc(s->null_termination ? '\0' : '\n', s->fp);
+			return;
+		}
 	}
 
 	base = branch->merge[0]->dst;
@@ -1392,6 +1394,11 @@ static void wt_shortstatus_print_tracking(struct wt_status *s)
 	color_fprintf(s->fp, header_color, "...");
 	color_fprintf(s->fp, branch_color_remote, "%s", base);
 
+	if (!num_ours && !num_theirs) {
+		fputc(s->null_termination ? '\0' : '\n', s->fp);
+		return;
+	}
+
 	color_fprintf(s->fp, header_color, " [");
 	if (!num_ours) {
 		color_fprintf(s->fp, header_color, _("behind "));
-- 
1.8.4.rc1.429.g46fb194