clone: use "quick" lookup while following tags

When cloning with --single-branch, we implement git-fetch's usual
tag-following behavior, grabbing any tag objects that point to objects
we have locally.

When we're a partial clone, though, our has_object_file() check will
actually lazy-fetch each tag. That not only defeats the purpose of
--single-branch, but it does it incredibly slowly, potentially kicking
off a new fetch for each tag. This is even worse for a shallow clone,
which implies --single-branch, because even tags which are supersets of
each other will be fetched individually.

We can fix this by passing OBJECT_INFO_SKIP_FETCH_OBJECT to the call,
which is what git-fetch does in this case.

Likewise, let's include OBJECT_INFO_QUICK, as that's what git-fetch
does. The rationale is discussed in 5827a03545 (fetch: use "quick"
has_sha1_file for tag following, 2016-10-13), but here the tradeoff
would apply even more so because clone is very unlikely to be racing
with another process repacking our newly-created repository.

This may provide a very small speedup even in the non-partial case case,
as we'd avoid calling reprepare_packed_git() for each tag (though in
practice, we'd only have a single packfile, so that reprepare should be
quite cheap).

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

diff --git a/builtin/clone.c b/builtin/clone.c
index 0fc89ae2b9c77d420153c8bef6680d3324cdf5ad..e568a7382b5dd87b501bb0d18aa53231a419d39a 100644 (file)
--- a/builtin/clone.c
+++ b/builtin/clone.c
@@ -639,7 +639,9 @@ static void write_followtags(const struct ref *refs, const char *msg)
                        continue;
                if (ends_with(ref->name, "^{}"))
                        continue;
-               if (!has_object_file(&ref->old_oid))
+               if (!has_object_file_with_flags(&ref->old_oid,
+                                               OBJECT_INFO_QUICK |
+                                               OBJECT_INFO_SKIP_FETCH_OBJECT))
                        continue;
                update_ref(msg, ref->name, &ref->old_oid, NULL, 0,
                           UPDATE_REFS_DIE_ON_ERR);

diff --git a/t/t5616-partial-clone.sh b/t/t5616-partial-clone.sh
index da3ad4e32a1ad5d8d03d3e37170d49c516cc611b..91322f3d97bec58aa2d99ae1b2edaa8ef59cb115 100755 (executable)
--- a/t/t5616-partial-clone.sh
+++ b/t/t5616-partial-clone.sh
@@ -405,6 +405,14 @@ test_expect_success 'verify fetch downloads only one pack when updating refs' '
        test_line_count = 3 pack-list
 '
 
+test_expect_success 'single-branch tag following respects partial clone' '
+       git clone --single-branch -b B --filter=blob:none \
+               "file://$(pwd)/srv.bare" single &&
+       git -C single rev-parse --verify refs/tags/B &&
+       git -C single rev-parse --verify refs/tags/A &&
+       test_must_fail git -C single rev-parse --verify refs/tags/C
+'
+
 . "$TEST_DIRECTORY"/lib-httpd.sh
 start_httpd