branch: report invalid tracking branch as gone

Command "git branch -vv" will report tracking branches, but invalid
tracking branches are also reported. This is because the function
stat_tracking_info() can not distinguish invalid tracking branch
from other cases which it would not like to report, such as
there is no upstream settings at all, or nothing is changed between
one branch and its upstream.

Junio suggested missing upstream should be reported [1] like:

    $ git branch -v -v
      master    e67ac84 initial
    * topic     3fc0f2a [topicbase: gone] topic

    $ git status
    # On branch topic
    # Your branch is based on 'topicbase', but the upstream is gone.
    #   (use "git branch --unset-upstream" to fixup)
    ...

    $ git status -b -s
    ## topic...topicbase [gone]
    ...

In order to do like that, we need to distinguish these three cases
(i.e. no tracking, with configured but no longer valid tracking, and
with tracking) in function stat_tracking_info(). So the refactored
function stat_tracking_info() has three return values: -1 (with "gone"
base), 0 (no base), and 1 (with base).

If the caller does not like to report tracking info when nothing
changed between the branch and its upstream, simply checks if
num_theirs and num_ours are both 0.

[1]: http://thread.gmane.org/gmane.comp.version-control.git/231830/focus=232288

Suggested-by: Junio C Hamano <gitster@pobox.com>
Signed-off-by: Jiang Xin <worldhello.net@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 46 insertions, 25 deletions

diff --git a/remote.c b/remote.c
index efcba931e..87c8dd35b 100644
--- a/remote.c
+++ b/remote.c
@@ -1695,7 +1695,11 @@ int ref_newer(const unsigned char *new_sha1, const unsigned char *old_sha1)
 }
 
 /*
- * Return true if there is anything to report, otherwise false.
+ * Compare a branch with its upstream, and save their differences (number
+ * of commits) in *num_ours and *num_theirs.
+ *
+ * Return 0 if branch has no upstream (no base), -1 if upstream is missing
+ * (with "gone" base), otherwise 1 (with base).
  */
 int stat_tracking_info(struct branch *branch, int *num_ours, int *num_theirs)
 {
@@ -1706,34 +1710,30 @@ int stat_tracking_info(struct branch *branch, int *num_ours, int *num_theirs)
 	const char *rev_argv[10], *base;
 	int rev_argc;
 
-	/*
-	 * Nothing to report unless we are marked to build on top of
-	 * somebody else.
-	 */
+	/* Cannot stat unless we are marked to build on top of somebody else. */
 	if (!branch ||
 	    !branch->merge || !branch->merge[0] || !branch->merge[0]->dst)
 		return 0;
 
-	/*
-	 * If what we used to build on no longer exists, there is
-	 * nothing to report.
-	 */
+	/* Cannot stat if what we used to build on no longer exists */
 	base = branch->merge[0]->dst;
 	if (read_ref(base, sha1))
-		return 0;
+		return -1;
 	theirs = lookup_commit_reference(sha1);
 	if (!theirs)
-		return 0;
+		return -1;
 
 	if (read_ref(branch->refname, sha1))
-		return 0;
+		return -1;
 	ours = lookup_commit_reference(sha1);
 	if (!ours)
-		return 0;
+		return -1;
 
 	/* are we the same? */
-	if (theirs == ours)
-		return 0;
+	if (theirs == ours) {
+		*num_theirs = *num_ours = 0;
+		return 1;
+	}
 
 	/* Run "rev-list --left-right ours...theirs" internally... */
 	rev_argc = 0;
@@ -1775,31 +1775,52 @@ int stat_tracking_info(struct branch *branch, int *num_ours, int *num_theirs)
  */
 int format_tracking_info(struct branch *branch, struct strbuf *sb)
 {
-	int num_ours, num_theirs;
+	int ours, theirs;
 	const char *base;
+	int upstream_is_gone = 0;
 
-	if (!stat_tracking_info(branch, &num_ours, &num_theirs))
+	switch (stat_tracking_info(branch, &ours, &theirs)) {
+	case 0:
+		/* no base */
 		return 0;
+	case -1:
+		/* with "gone" base */
+		upstream_is_gone = 1;
+		break;
+	default:
+		/* Nothing to report if neither side has changes. */
+		if (!ours && !theirs)
+			return 0;
+		/* with base */
+		break;
+	}
 
 	base = branch->merge[0]->dst;
 	base = shorten_unambiguous_ref(base, 0);
-	if (!num_theirs) {
+	if (upstream_is_gone) {
+		strbuf_addf(sb,
+			_("Your branch is based on '%s', but the upstream is gone.\n"),
+			base);
+		if (advice_status_hints)
+			strbuf_addf(sb,
+				_("  (use \"git branch --unset-upstream\" to fixup)\n"));
+	} else if (!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",
-			   num_ours),
-			base, num_ours);
+			   ours),
+			base, ours);
 		if (advice_status_hints)
 			strbuf_addf(sb,
 				_("  (use \"git push\" to publish your local commits)\n"));
-	} else if (!num_ours) {
+	} else if (!ours) {
 		strbuf_addf(sb,
 			Q_("Your branch is behind '%s' by %d commit, "
 			       "and can be fast-forwarded.\n",
 			   "Your branch is behind '%s' by %d commits, "
 			       "and can be fast-forwarded.\n",
-			   num_theirs),
-			base, num_theirs);
+			   theirs),
+			base, theirs);
 		if (advice_status_hints)
 			strbuf_addf(sb,
 				_("  (use \"git pull\" to update your local branch)\n"));
@@ -1811,8 +1832,8 @@ int format_tracking_info(struct branch *branch, struct strbuf *sb)
 			   "Your branch and '%s' have diverged,\n"
 			       "and have %d and %d different commits each, "
 			       "respectively.\n",
-			   num_theirs),
-			base, num_ours, num_theirs);
+			   theirs),
+			base, ours, theirs);
 		if (advice_status_hints)
 			strbuf_addf(sb,
 				_("  (use \"git pull\" to merge the remote branch into yours)\n"));