[PATCH 2 of 6] export: invoke the file prefetch hook

[Matt Harbison]

> On Apr 16, 2018, at 7:31 AM, Yuya Nishihara <yuya at tcha.org> wrote:
> 
>> On Sun, 15 Apr 2018 02:44:06 -0400, Matt Harbison wrote:
>> # HG changeset patch
>> # User Matt Harbison <matt_harbison at yahoo.com>
>> # Date 1523749425 14400
>> #      Sat Apr 14 19:43:45 2018 -0400
>> # Node ID 1c3654f7ed31e6770cbd97681083bab834554056
>> # Parent  de2975df3997148a832ef41425b069fc6f8ff3bc
>> export: invoke the file prefetch hook
>> 
>> cmdutil.exportfile() is only called by shelve, mq and patchbomb.  Those are
>> unlikely to mix with lfs, but it may as well be invoked there for completeness.
>> 
>> diff --git a/mercurial/cmdutil.py b/mercurial/cmdutil.py
>> --- a/mercurial/cmdutil.py
>> +++ b/mercurial/cmdutil.py
>> @@ -1619,6 +1619,12 @@ def export(repo, revs, basefm, fntemplat
>>                             the given template.
>>         Otherwise: All revs will be written to basefm.
>>     '''
>> +    files = None
>> +    ctxs = [repo[r] for r in revs]
>> +    if match:
>> +        files = set([f for ctx in ctxs for f in ctx if match(f)])
>> +    scmutil.fileprefetchhooks(repo, ctxs, files)
> 
> Perhaps we'll need
> 
>  fileprefetchhooks(repo, revs, match)
> 
> since it may take some time to build a list of ctxs and files.

All of the callers other than export and verify already have ctx.  Does it make sense to ctx -> rev -> ctx like that?

I really like the idea of using match (in fact, I started coding it up). But I stopped when either diff or export printed a “no such file in rev $hash” message.  I was also a little concerned with not undermining how cat will extract a single file from the matcher as an optimization.  But I guess we can fix that later.

Wrapping in match.badmatch() works, so I’ll try that again.

> We can reconstruct a matcher from files by scmutil.matchfiles().

Presumably we should only do that for things like revert, that are building their own file list?  I’m assuming that using the available matcher for commands where there is one is ok.