Re: [PATCH 1/3] revision: complicated pathspecs disable filters

[Derrick Stolee <stolee@gmail.com>]

On 4/12/2020 8:07 PM, Taylor Blau wrote:
> On Sun, Apr 12, 2020 at 03:30:07PM -0700, Junio C Hamano wrote:
>> Taylor Blau <me@ttaylorr.com> writes:
>>
>>> I certainly wouldn't complain about a comment here explaining these
>>> three checks, but I suppose that the rationale is only a 'git blame'
>>> away (and I guess that is faster now after this series ;-)).
>>>
>>>> +	if (revs->prune_data.has_wildcard)
>>>> +		return;
>>>> +	if (revs->prune_data.nr > 1)
>>>> +		return;
>>>> +	if (revs->prune_data.magic ||
>>>> +	    (revs->prune_data.nr &&
>>>> +	     revs->prune_data.items[0].magic))
>>
>> This says "any magic", but it is overly pessimistic to disable the
>> optimization for "literal" magic.  That magic is the one that lets
>> well written scripts to say "I have in a '$variable' that the user
>> gave me as a pathname (not pathspec), and it may have a wildcard
>> letter in it, but please treat it as a literal string" by prefixing
>> ":(literal)" before that user-supplied data, so it is punishing well
>> disciplined folks.

This is a good point. I'm unfamiliar with these advanced pathspec
tricks.

> I hadn't thought of that, but it makes sense to me. How about something
> like this squashed into this patch? I moved the if-chain that Stolee
> introduced out to its own function, at least since they seem
> well-contained and related to one another. I figure that this simplifies
> the implementation of 'prepare_to_use_bloom_filter' by giving the reader
> less to think about up-front.
> 
> diff --git a/revision.c b/revision.c
> index 534c0bf996..15bf4ccff5 100644
> --- a/revision.c
> +++ b/revision.c
> @@ -654,6 +654,18 @@ static void trace2_bloom_filter_statistics_atexit(void)
>         jw_release(&jw);
>  }
> 
> +static int has_bloom_key(struct pathspec *spec)
> +{
> +       if (spec->has_wildcard)
> +               return 0;
> +       if (spec->nr > 1)
> +               return 0;
> +       if ((spec->magic & ~PATHSPEC_LITERAL) ||
> +           (spec->nr && spec->items[0].magic & ~PATHSPEC_LITERAL))
> +               return 0;
> +       return 1;
> +}
> +

Perhaps flip this on its head?

+static int forbids_bloom_key(struct pathspec *spec)
+{
+       if (spec->has_wildcard)
+               return 1;
+       if (spec->nr > 1)
+               return 1;
+       if (spec->magic & ~PATHSPEC_LITERAL)
+		return 1;
+	if (spec->nr && (spec->items[0].magic & ~PATHSPEC_LITERAL))
+               return 1;
+       return 0;
+}
+

>  static void prepare_to_use_bloom_filter(struct rev_info *revs)
>  {
>         struct pathspec_item *pi;
> @@ -665,13 +677,7 @@ static void prepare_to_use_bloom_filter(struct rev_info *revs)
>         if (!revs->commits)
>             return;
> 
> -       if (revs->prune_data.has_wildcard)
> -               return;
> -       if (revs->prune_data.nr > 1)
> -               return;
> -       if (revs->prune_data.magic ||
> -           (revs->prune_data.nr &&
> -            revs->prune_data.items[0].magic))
> +       if (!has_bloom_key(&revs->prune_data))
>                 return;

Then this would be "if (forbids_bloom_key(&revs->prune_data))"

Generally, I like pulling this stuff out as a method to isolate and
label its purpose. If we wanted to allow certain :(icase) things
later, then we know what to modify in order to "allow" it.

Thanks,
-Stolee