branch: show upstream branch when double verbose

This information is easily accessible when we are
calculating the relationship. The only reason not to print
it all the time is that it consumes a fair bit of screen
space, and may not be of interest to the user.

Signed-off-by: Jeff King <peff@peff.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

Documentation/git-branch.txt

@@ -100,7 +100,9 @@ OPTIONS
 
 -v::
 --verbose::
-	Show sha1 and commit subject line for each head.
+	Show sha1 and commit subject line for each head, along with
+	relationship to upstream branch (if any). If given twice, print
+	the name of the upstream branch, as well.
 
 --abbrev=<length>::
 	Alter the sha1's minimum display length in the output listing.

builtin-branch.c

@@ -301,19 +301,30 @@ static int ref_cmp(const void *r1, const void *r2)
 	return strcmp(c1->name, c2->name);
 }
 
-static void fill_tracking_info(struct strbuf *stat, const char *branch_name)
+static void fill_tracking_info(struct strbuf *stat, const char *branch_name,
+		int show_upstream_ref)
 {
 	int ours, theirs;
 	struct branch *branch = branch_get(branch_name);
 
-	if (!stat_tracking_info(branch, &ours, &theirs) || (!ours && !theirs))
+	if (!stat_tracking_info(branch, &ours, &theirs)) {
+		if (branch && branch->merge && branch->merge[0]->dst &&
+		    show_upstream_ref)
+			strbuf_addf(stat, "[%s] ",
+			    shorten_unambiguous_ref(branch->merge[0]->dst));
 		return;
+	}
+
+	strbuf_addch(stat, '[');
+	if (show_upstream_ref)
+		strbuf_addf(stat, "%s: ",
+			shorten_unambiguous_ref(branch->merge[0]->dst));
 	if (!ours)
-		strbuf_addf(stat, "[behind %d] ", theirs);
+		strbuf_addf(stat, "behind %d] ", theirs);
 	else if (!theirs)
-		strbuf_addf(stat, "[ahead %d] ", ours);
+		strbuf_addf(stat, "ahead %d] ", ours);
 	else
-		strbuf_addf(stat, "[ahead %d, behind %d] ", ours, theirs);
+		strbuf_addf(stat, "ahead %d, behind %d] ", ours, theirs);
 }
 
 static int matches_merge_filter(struct commit *commit)
@@ -379,7 +390,7 @@ static void print_ref_item(struct ref_item *item, int maxwidth, int verbose,
 		}
 
 		if (item->kind == REF_LOCAL_BRANCH)
-			fill_tracking_info(&stat, item->name);
+			fill_tracking_info(&stat, item->name, verbose > 1);
 
 		strbuf_addf(&out, " %s %s%s",
 			find_unique_abbrev(item->commit->object.sha1, abbrev),