Re: [PATCH v3 17/25] t/helper/test-read-midx.c: add --checksum mode

On Thu, Aug 12, 2021 at 04:31:18PM -0400, Jeff King wrote:

On Tue, Jul 27, 2021 at 05:20:07PM -0400, Taylor Blau wrote:

quoted

Subsequent tests will want to check for the existence of a multi-pack
bitmap which matches the multi-pack-index stored in the pack directory.

The multi-pack bitmap includes the hex checksum of the MIDX it
corresponds to in its filename (for example,
'$packdir/multi-pack-index-<checksum>.bitmap'). As a result, some tests
want a way to learn what '<checksum>' is.

This helper addresses that need by printing the checksum of the
repository's multi-pack-index.

Makes sense. It might be nice to have a generic tool for pulling hashes
out of checksum files. Perhaps even a tool that is shipped with Git for
operating on such files (for in-the-field debugging and diagnosis). But
that can definitely be separate from this series (if ever).

Yeah. That would definitely be in the spirit of "we should have more
test-tool-like helpers exposed via user-facing plumbing". And I agree
that it would be nice, but I definitely agree that it's a topic for a
later date ;).

quoted

 t/helper/test-read-midx.c | 16 +++++++++++++++-
 t/lib-bitmap.sh           |  4 ++++
 2 files changed, 19 insertions(+), 1 deletion(-)

The patch itself looks fine to me. One curiosity:

quoted

diff --git a/t/lib-bitmap.sh b/t/lib-bitmap.sh
index ecb5d0e05d..09cd036f4d 100644
--- a/t/lib-bitmap.sh
+++ b/t/lib-bitmap.sh

@@ -260,3 +260,7 @@ have_delta () {
 	echo $1 | git cat-file --batch-check="%(deltabase)" >actual &&
 	test_cmp expect actual
 }
+
+midx_checksum () {
+	test-tool read-midx --checksum "${1:-.git/objects}"
+}

This default ".git/objects" will only _usually_ be the right thing. :)
If the actual C code accepted a missing object-dir, it could use the
correct object directory discovered by setup_git_directory().

Probably not a big deal either way, though.

Yeah. We could just sidestep the whole thing by not having the
`.git/objects` default, since all callers of midx_checksum pass an
argument, so that fallback is dead code anyway. Thanks for noting, I'll
remove it for the next round.

Thanks,
Taylor