Re: [PATCH v2] remote: make refspec follow the same disambiguation rule as local refs

From: Jonathan Nieder <jrnieder@gmail.com>
Date: Aug 1, 2018, 23:08 UTC
Message-ID: <20180801230802.GC189024@aiede.svl.corp.google.com>
In-Reply-To: <xmqq8t5q821c.fsf@gitster-ct.c.googlers.com>

Hi,

Junio C Hamano 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 any DWIM rules used by refname_match() in refs.c, even if a
> better match occurs later in the list of refs.

Nicely explained.

[...]

Show 18 quoted lines

> --- a/refs.c
> +++ b/refs.c
> @@ -487,16 +487,22 @@ static const char *ref_rev_parse_rules[] = {
>  	NULL
>  };
>  
> +/*
> + * Is it possible that the caller meant full_name with abbrev_name?
> + * If so return a non-zero value to signal "yes"; the magnitude of
> + * the returned value gives the precedence used for disambiguation.
> + *
> + * If abbrev_name cannot mean full_name, return 0.
> + */
>  int refname_match(const char *abbrev_name, const char *full_name)
>  {
>  	const char **p;
>  	const int abbrev_name_len = strlen(abbrev_name);
> +	const int num_rules = ARRAY_SIZE(ref_rev_parse_rules) - 1;

This is assuming ref_rev_parse_rules consists exactly of its items followed by a NULL terminator, which is potentially a bit subtle. I wonder if we should put

	static const char *ref_rev_parse_rules[] = {
		"%.*s",
		"refs/%.*s",
		"refs/tags/%.*s",
		"refs/heads/%.*s",
		"refs/remotes/%.*s",
		"refs/remotes/%.*s/HEAD",
		NULL
	};
	#define NUM_REV_PARSE_RULES (ARRAY_SIZE(ref_rev_parse_rules) - 1)

and then use something like

	const int num_rules = NUM_REV_PARSE_RULES;

so that this dependency is more obvious if the ref_rev_parse_rules convention changes later.

Alternatively, what would you think of using the simpler return convention

	return p - ref_rev_parse_rules + 1;

?  Or even

	return p - ref_rev_parse_rules;

and -1 for "no match"?

[...]

Show 21 quoted lines

> --- a/remote.c
> +++ b/remote.c
> @@ -1880,11 +1880,18 @@ 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 *ref;
> +	const struct ref *best_match = NULL;
> +	int best_score = 0;
> +
>  	for (ref = refs; ref; ref = ref->next) {
> -		if (refname_match(name, ref->name))
> -			return ref;
> +		int score = refname_match(name, ref->name);
> +
> +		if (best_score < score) {
> +			best_match = ref;
> +			best_score = score;
> +		}
>  	}
> -	return NULL;
> +	return best_match;

Sensible and simple. If we wanted to make items earlier in the list return a lower value from refname_match, then we'd need a !best_score test here, which might be what motivates that return value convention.

[...]

Show 7 quoted lines

> --- a/t/t5510-fetch.sh
> +++ b/t/t5510-fetch.sh
> @@ -535,6 +535,41 @@ test_expect_success "should be able to fetch with duplicate refspecs" '
>  	)
>  '
>  
> +test_expect_success 'LHS of refspec follows ref disambiguation rules' '

Clearly illustrates the bug this fixes, in a way that makes it obvious that a user would prefer the new behavior. Good.

With or without the tweak of introducing NUM_REV_PARSE_RULES mentioned above,

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

Thanks.