name-rev: include taggerdate in considering the best name

We most likely want the oldest tag that contained the commit to be
reported. So let's remember the taggerdate, and make it more important
than anything else when choosing the best name for a given commit.

Suggested by Linus Torvalds.

Note that we need to update t9903 because it tested for the old behavior
(which preferred the description "b1~1" over "tags/t2~1").

We might want to introduce a --heed-taggerdate option, and make the new
behavior dependent on that, if it turns out that some scripts rely on the
old name-rev method.

Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin/name-rev.c

@@ -10,6 +10,7 @@
 
 typedef struct rev_name {
 	const char *tip_name;
+	unsigned long taggerdate;
 	int generation;
 	int distance;
 } rev_name;
@@ -20,7 +21,8 @@ static long cutoff = LONG_MAX;
 #define MERGE_TRAVERSAL_WEIGHT 65535
 
 static void name_rev(struct commit *commit,
-		const char *tip_name, int generation, int distance,
+		const char *tip_name, unsigned long taggerdate,
+		int generation, int distance,
 		int deref)
 {
 	struct rev_name *name = (struct rev_name *)commit->util;
@@ -43,9 +45,12 @@ static void name_rev(struct commit *commit,
 		name = xmalloc(sizeof(rev_name));
 		commit->util = name;
 		goto copy_data;
-	} else if (name->distance > distance) {
+	} else if (name->taggerdate > taggerdate ||
+			(name->taggerdate == taggerdate &&
+			 name->distance > distance)) {
 copy_data:
 		name->tip_name = tip_name;
+		name->taggerdate = taggerdate;
 		name->generation = generation;
 		name->distance = distance;
 	} else
@@ -70,11 +75,11 @@ copy_data:
 				sprintf(new_name, "%.*s^%d", len, tip_name,
 						parent_number);
 
-			name_rev(parents->item, new_name, 0,
+			name_rev(parents->item, new_name, taggerdate, 0,
 				distance + MERGE_TRAVERSAL_WEIGHT, 0);
 		} else {
-			name_rev(parents->item, tip_name, generation + 1,
-				distance + 1, 0);
+			name_rev(parents->item, tip_name, taggerdate,
+				generation + 1, distance + 1, 0);
 		}
 	}
 }
@@ -144,6 +149,7 @@ static int name_ref(const char *path, const unsigned char *sha1, int flags, void
 	struct name_ref_data *data = cb_data;
 	int can_abbreviate_output = data->tags_only && data->name_only;
 	int deref = 0;
+	unsigned long taggerdate = ULONG_MAX;
 
 	if (data->tags_only && !starts_with(path, "refs/tags/"))
 		return 0;
@@ -168,12 +174,13 @@ static int name_ref(const char *path, const unsigned char *sha1, int flags, void
 			break; /* broken repository */
 		o = parse_object(t->tagged->sha1);
 		deref = 1;
+		taggerdate = t->date;
 	}
 	if (o && o->type == OBJ_COMMIT) {
 		struct commit *commit = (struct commit *)o;
 
 		path = name_ref_abbrev(path, can_abbreviate_output);
-		name_rev(commit, xstrdup(path), 0, 0, deref);
+		name_rev(commit, xstrdup(path), taggerdate, 0, 0, deref);
 	}
 	return 0;
 }

t/t9903-bash-prompt.sh

@@ -107,7 +107,7 @@ test_expect_success 'prompt - describe detached head - contains' '
 '
 
 test_expect_success 'prompt - describe detached head - branch' '
-	printf " ((b1~1))" >expected &&
+	printf " ((tags/t2~1))" >expected &&
 	git checkout b1^ &&
 	test_when_finished "git checkout master" &&
 	(