[PATCH] revset: use manifest.matches in _follow revset

[Durham Goode]

On 2/5/16 1:22 PM, Martin von Zweigbergk wrote:
> On Fri, Feb 5, 2016 at 12:47 PM, Durham Goode <durham at fb.com> wrote:
>> # HG changeset patch
>> # User Durham Goode <durham at fb.com>
>> # Date 1454705079 28800
>> #      Fri Feb 05 12:44:39 2016 -0800
>> # Node ID 4bf06bc950fcbee8fc65cd3fd17d366a27603ad9
>> # Parent  01a5143cd25f285f8c745a92986cd7186bb32c90
>> revset: use manifest.matches in _follow revset
>>
>> The old _follow revset iterated over every file in the commit and checked if it
>> matched. For repos with large manifests, this could take 500ms. By switching to
>> use manifest.matches() we can take advantage of the fastpaths built in to
>> manifest.py that allows iterating over only the files in the matcher when it's a
>> simple matcher. This brings the time spent down from 500ms to 0ms during simple
>> operations like 'hg log -f file.txt'.
> Nice!
>
>> diff --git a/mercurial/revset.py b/mercurial/revset.py
>> --- a/mercurial/revset.py
>> +++ b/mercurial/revset.py
>> @@ -1086,13 +1086,14 @@ def _follow(repo, subset, x, name, follo
>>           matcher = matchmod.match(repo.root, repo.getcwd(), [x],
>>                                    ctx=repo[None], default='path')
>>
>> +        files = c.manifest().matches(matcher)
> I think you can even use c.manifest.walk(matcher) here to avoid
> creating the manifest. Obviously we don't need it to be faster than
> 0ms, but perhaps it would be noticeable when many files are matched.
> I'll leave it to you to test or just dismiss that.
>
Interesting.  It's probably doesn't matter for this revset, but it's a 
good idea regardless.  I'll send a V2 with that.