Re: [PATCH] remote: prefer exact matches when using refspecs

[Jonathan Nieder <jrnieder@gmail.com>]

Hi,

Jonathan Tan wrote:

> When matching a non-wildcard LHS of a refspec against a list of refs,
> find_ref_by_name_abbrev() returns the first ref that matches using the
> DWIM rules used by refname_match() in refs.c, even if an exact match
> occurs later in the list of refs.
>
> This causes unexpected behavior when (for example) fetching using the
> refspec "refs/heads/s:<something>" from a remote with both
> "refs/heads/refs/heads/s" and "refs/heads/s". (Even if the former was
> inadvertently created, one would still expect the latter to be fetched.)
>
> This problem has only been observed when the desired ref comes after the
> undesired ref in alphabetical order. However, for completeness, the test
> in this patch also checks what happens when the desired ref comes first
> alphabetically.
>
> Signed-off-by: Jonathan Tan <jonathantanmy@google.com>
> ---
>  remote.c         |  7 +++++--
>  t/t5510-fetch.sh | 28 ++++++++++++++++++++++++++++
>  2 files changed, 33 insertions(+), 2 deletions(-)

Very clear analysis --- thank you.

> --- a/remote.c
> +++ b/remote.c
> @@ -1687,12 +1687,15 @@ static struct ref *get_expanded_map(const struct ref *remote_refs,
>  
>  static const struct ref *find_ref_by_name_abbrev(const struct ref *refs, const char *name)
>  {
> +	const struct ref *best_match = NULL;
>  	const struct ref *ref;
>  	for (ref = refs; ref; ref = ref->next) {
> -		if (refname_match(name, ref->name))
> +		if (!strcmp(name, ref->name))
>  			return ref;
> +		if (refname_match(name, ref->name))

Should this check be

		if (!best_match && refname_match(name, ref->name))

?  Otherwise, this would make us prefer the last ref instead of the
first (which probably doesn't matter but would be an unintended
behavior change).

> +			best_match = ref;
>  	}
> -	return NULL;
> +	return best_match;
>  }
>  
>  struct ref *get_remote_ref(const struct ref *remote_refs, const char *name)
> diff --git a/t/t5510-fetch.sh b/t/t5510-fetch.sh
> index e402aee6a..da88f35f0 100755
> --- a/t/t5510-fetch.sh
> +++ b/t/t5510-fetch.sh
> @@ -535,6 +535,34 @@ test_expect_success "should be able to fetch with duplicate refspecs" '
>  	)
>  '
>  
> +test_expect_success 'LHS of refspec prefers exact matches' '

Nice.

With or without the suggested tweak,

Reviewed-by: Jonathan Nieder <jrnieder@gmail.com>

Thanks for a pleasant read.

> +	mkdir lhs-exact &&
> +	(
> +		cd lhs-exact &&
> +		git init server &&
> +		test_commit -C server unwanted &&
> +		test_commit -C server wanted &&
> +
> +		git init client &&
> +
> +		# Check a name coming after "refs" alphabetically ...
> +		git -C server update-ref refs/heads/s wanted &&
> +		git -C server update-ref refs/heads/refs/heads/s unwanted &&
> +		git -C client fetch ../server refs/heads/s:refs/heads/checkthis &&
> +		git -C server rev-parse wanted >expect &&
> +		git -C client rev-parse checkthis >actual &&
> +		test_cmp expect actual &&
> +
> +		# ... and one before.
> +		git -C server update-ref refs/heads/q wanted &&
> +		git -C server update-ref refs/heads/refs/heads/q unwanted &&
> +		git -C client fetch ../server refs/heads/q:refs/heads/checkthis &&
> +		git -C server rev-parse wanted >expect &&
> +		git -C client rev-parse checkthis >actual &&
> +		test_cmp expect actual
> +	)
> +'
> +
>  # configured prune tests
>  
>  set_config_tristate () {