repack: simplify handling of auto-bitmaps and .keep files

Commit 7328482253 (repack: disable bitmaps-by-default if .keep files
exist, 2019-06-29) taught repack to prefer disabling bitmaps to
duplicating objects (unless bitmaps were asked for explicitly).

But there's an easier way to do this: if we keep passing the
--honor-pack-keep flag to pack-objects when auto-enabling bitmaps, then
pack-objects already makes the same decision (it will disable bitmaps
rather than duplicate). Better still, pack-objects can actually decide
to do so based not just on the presence of a .keep file, but on whether
that .keep file actually impacts the new pack we're making (so if we're
racing with a push or fetch, for example, their temporary .keep file
will not block us from generating bitmaps if they haven't yet updated
their refs).

And because repack uses the --write-bitmap-index-quiet flag, we don't
have to worry about pack-objects generating confusing warnings when it
does see a .keep file. We can confirm this by tweaking the .keep test to
check repack's stderr.

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

builtin/repack.c

@@ -89,17 +89,6 @@ static void remove_pack_on_signal(int signo)
 	raise(signo);
 }
 
-static int has_pack_keep_file(void)
-{
-	struct packed_git *p;
-
-	for (p = get_all_packs(the_repository); p; p = p->next) {
-		if (p->pack_keep)
-			return 1;
-	}
-	return 0;
-}
-
 /*
  * Adds all packs hex strings to the fname list, which do not
  * have a corresponding .keep file. These packs are not to
@@ -346,13 +335,11 @@ int cmd_repack(int argc, const char **argv, const char *prefix)
 
 	if (write_bitmaps < 0) {
 		if (!(pack_everything & ALL_INTO_ONE) ||
-		    !is_bare_repository() ||
-		    keep_pack_list.nr != 0 ||
-		    has_pack_keep_file())
+		    !is_bare_repository())
 			write_bitmaps = 0;
 	}
 	if (pack_kept_objects < 0)
-		pack_kept_objects = !!write_bitmaps;
+		pack_kept_objects = write_bitmaps > 0;
 
 	if (write_bitmaps && !(pack_everything & ALL_INTO_ONE))
 		die(_(incremental_bitmap_conflict_error));

t/t7700-repack.sh

@@ -245,7 +245,8 @@ test_expect_success 'no bitmaps created if .keep files present' '
 	keep=${pack%.pack}.keep &&
 	test_when_finished "rm -f \"\$keep\"" &&
 	>"$keep" &&
-	git -C bare.git repack -ad &&
+	git -C bare.git repack -ad 2>stderr &&
+	test_must_be_empty stderr &&
 	find bare.git/objects/pack/ -type f -name "*.bitmap" >actual &&
 	test_must_be_empty actual
 '