Subject: Re: [PATCH v2 1/4] ref-cache.c: fix prefix matching in ref iteration

From: Patrick Steinhardt <[email-masked]>
Date: Tue, 10 Oct 2023 09:21:12 +0200

On Mon, Oct 09, 2023 at 09:58:53PM +0000, Victoria Dye via GitGitGadget wrote:
> From: Victoria Dye <[email-masked]>
> 
> Update 'cache_ref_iterator_advance' to skip over refs that are not matched
> by the given prefix.
> 
> Currently, a ref entry is considered "matched" if the entry name is fully
> contained within the prefix:
> 
> * prefix: "refs/heads/v1"
> * entry: "refs/heads/v1.0"
> 
> OR if the prefix is fully contained in the entry name:
> 
> * prefix: "refs/heads/v1.0"
> * entry: "refs/heads/v1"
> 
> The first case is always correct, but the second is only correct if the ref
> cache entry is a directory, for example:
> 
> * prefix: "refs/heads/example"
> * entry: "refs/heads/"
> 
> Modify the logic in 'cache_ref_iterator_advance' to reflect these
> expectations:
> 
> 1. If 'overlaps_prefix' returns 'PREFIX_EXCLUDES_DIR', then the prefix and
>    ref cache entry do not overlap at all. Skip this entry.
> 2. If 'overlaps_prefix' returns 'PREFIX_WITHIN_DIR', then the prefix matches
>    inside this entry if it is a directory. Skip if the entry is not a
>    directory, otherwise iterate over it.
> 3. Otherwise, 'overlaps_prefix' returned 'PREFIX_CONTAINS_DIR', indicating
>    that the cache entry (directory or not) is fully contained by or equal to
>    the prefix. Iterate over this entry.
> 
> Note that condition 2 relies on the names of directory entries having the
> appropriate trailing slash. The existing function documentation of
> 'create_dir_entry' explicitly calls out the trailing slash requirement, so
> this is a safe assumption to make.
> 
> This bug generally doesn't have any user-facing impact, since it requires:
> 
> 1. using a non-empty prefix without a trailing slash in an iteration like
>    'for_each_fullref_in',
> 2. the callback to said iteration not reapplying the original filter (as
>    for-each-ref does) to ensure unmatched refs are skipped, and
> 3. the repository having one or more refs that match part of, but not all
>    of, the prefix.
> 
> However, there are some niche scenarios that meet those criteria
> (specifically, 'rev-parse --bisect' and '(log|show|shortlog) --bisect'). Add
> tests covering those cases to demonstrate the fix in this patch.
> 
> Signed-off-by: Victoria Dye <[email-masked]>
> ---
>  refs/ref-cache.c              |  3 ++-
>  t/t1500-rev-parse.sh          | 23 +++++++++++++++++++++++
>  t/t4205-log-pretty-formats.sh | 30 ++++++++++++++++++++++++++++++
>  3 files changed, 55 insertions(+), 1 deletion(-)
> 
> diff --git a/refs/ref-cache.c b/refs/ref-cache.c
> index 2294c4564fb..6e3b725245c 100644
> --- a/refs/ref-cache.c
> +++ b/refs/ref-cache.c
> @@ -412,7 +412,8 @@ static int cache_ref_iterator_advance(struct ref_iterator *ref_iterator)
>  
>  		if (level->prefix_state == PREFIX_WITHIN_DIR) {
>  			entry_prefix_state = overlaps_prefix(entry->name, iter->prefix);
> -			if (entry_prefix_state == PREFIX_EXCLUDES_DIR)
> +			if (entry_prefix_state == PREFIX_EXCLUDES_DIR ||
> +			    (entry_prefix_state == PREFIX_WITHIN_DIR && !(entry->flag & REF_DIR)))
>  				continue;
>  		} else {
>  			entry_prefix_state = level->prefix_state;
> diff --git a/t/t1500-rev-parse.sh b/t/t1500-rev-parse.sh
> index 37ee5091b5c..3f9e7f62e45 100755
> --- a/t/t1500-rev-parse.sh
> +++ b/t/t1500-rev-parse.sh
> @@ -264,4 +264,27 @@ test_expect_success 'rev-parse --since= unsqueezed ordering' '
>  	test_cmp expect actual
>  '
>  
> +test_expect_success 'rev-parse --bisect includes bad, excludes good' '
> +	test_commit_bulk 6 &&
> +
> +	git update-ref refs/bisect/bad-1 HEAD~1 &&
> +	git update-ref refs/bisect/b HEAD~2 &&
> +	git update-ref refs/bisect/bad-3 HEAD~3 &&
> +	git update-ref refs/bisect/good-3 HEAD~3 &&
> +	git update-ref refs/bisect/bad-4 HEAD~4 &&
> +	git update-ref refs/bisect/go HEAD~4 &&
> +
> +	# Note: refs/bisect/b and refs/bisect/go should be ignored because they
> +	# do not match the refs/bisect/bad or refs/bisect/good prefixes.
> +	cat >expect <<-EOF &&
> +	refs/bisect/bad-1
> +	refs/bisect/bad-3
> +	refs/bisect/bad-4
> +	^refs/bisect/good-3
> +	EOF
> +
> +	git rev-parse --symbolic-full-name --bisect >actual &&
> +	test_cmp expect actual
> +'
> +
>  test_done
> diff --git a/t/t4205-log-pretty-formats.sh b/t/t4205-log-pretty-formats.sh
> index 16626e4fe96..62c7bfed5d7 100755
> --- a/t/t4205-log-pretty-formats.sh
> +++ b/t/t4205-log-pretty-formats.sh
> @@ -956,6 +956,36 @@ test_expect_success '%S in git log --format works with other placeholders (part
>  	test_cmp expect actual
>  '
>  
> +test_expect_success 'setup more commits for %S with --bisect' '
> +	test_commit four &&
> +	test_commit five &&
> +
> +	head1=$(git rev-parse --verify HEAD~0) &&
> +	head2=$(git rev-parse --verify HEAD~1) &&
> +	head3=$(git rev-parse --verify HEAD~2) &&
> +	head4=$(git rev-parse --verify HEAD~3)
> +'
> +
> +test_expect_success '%S with --bisect labels commits with refs/bisect/bad ref' '
> +	git update-ref refs/bisect/bad-$head1 $head1 &&
> +	git update-ref refs/bisect/go $head1 &&
> +	git update-ref refs/bisect/bad-$head2 $head2 &&
> +	git update-ref refs/bisect/b $head3 &&
> +	git update-ref refs/bisect/bad-$head4 $head4 &&
> +	git update-ref refs/bisect/good-$head4 $head4 &&
> +
> +	# We expect to see the range of commits betwee refs/bisect/good-$head4

Nit: s/betwee/between. Probably not worth rerolling this series only
because of this typo though.

Patrick

> +	# and refs/bisect/bad-$head1. The "source" ref is the nearest bisect ref
> +	# from which the commit is reachable.
> +	cat >expect <<-EOF &&
> +	$head1 refs/bisect/bad-$head1
> +	$head2 refs/bisect/bad-$head2
> +	$head3 refs/bisect/bad-$head2
> +	EOF
> +	git log --bisect --format="%H %S" >actual &&
> +	test_cmp expect actual
> +'
> +
>  test_expect_success 'log --pretty=reference' '
>  	git log --pretty="tformat:%h (%s, %as)" >expect &&
>  	git log --pretty=reference >actual &&
> -- 
> gitgitgadget
>