pack-objects: don't loosen objects available in alternate or kept packs

If pack-objects is called with the --unpack-unreachable option then it
will unpack (i.e. loosen) all unreferenced objects from local not-kept
packs, including those that also exist in packs residing in an alternate
object database or a locally kept pack.  The only user of this option is
git-repack.

In this case, repack will follow the call to pack-objects with a call to
prune-packed, which will delete these newly loosened objects, making the
act of loosening a waste of time.  The unnecessary loosening can be
avoided by checking whether an object exists in a non-local pack or a
locally kept pack before loosening it.

This fixes the 'local packed unreachable obs that exist in alternate ODB
are not loosened' test in t7700.

Signed-off-by: Brandon Casey <drafnel@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin-pack-objects.c

@@ -1944,6 +1944,29 @@ static void add_objects_in_unpacked_packs(struct rev_info *revs)
 	free(in_pack.array);
 }
 
+static int has_sha1_pack_kept_or_nonlocal(const unsigned char *sha1)
+{
+	static struct packed_git *last_found = (void *)1;
+	struct packed_git *p;
+
+	p = (last_found != (void *)1) ? last_found : packed_git;
+
+	while (p) {
+		if ((!p->pack_local || p->pack_keep) &&
+			find_pack_entry_one(sha1, p)) {
+			last_found = p;
+			return 1;
+		}
+		if (p == last_found)
+			p = packed_git;
+		else
+			p = p->next;
+		if (p == last_found)
+			p = p->next;
+	}
+	return 0;
+}
+
 static void loosen_unused_packed_objects(struct rev_info *revs)
 {
 	struct packed_git *p;
@@ -1959,7 +1982,8 @@ static void loosen_unused_packed_objects(struct rev_info *revs)
 
 		for (i = 0; i < p->num_objects; i++) {
 			sha1 = nth_packed_object_sha1(p, i);
-			if (!locate_object_entry(sha1))
+			if (!locate_object_entry(sha1) &&
+				!has_sha1_pack_kept_or_nonlocal(sha1))
 				if (force_object_loose(sha1, p->mtime))
 					die("unable to force loose object");
 		}

t/t7700-repack.sh

@@ -113,7 +113,7 @@ test_expect_success 'packed unreachable obs in alternate ODB are not loosened' '
 	test_must_fail git show $csha1
 '
 
-test_expect_failure 'local packed unreachable obs that exist in alternate ODB are not loosened' '
+test_expect_success 'local packed unreachable obs that exist in alternate ODB are not loosened' '
 	echo `pwd`/alt_objects > .git/objects/info/alternates &&
 	echo "$csha1" | git pack-objects --non-empty --all --reflog pack &&
 	rm -f .git/objects/pack/* &&