[PATCH V2] localrepo: avoid unnecessary conversion from node to rev

[Yuya Nishihara]

On Tue, 7 Feb 2017 13:11:23 -0800, Jun Wu wrote:
> V1 was accepted and in hg-committed [1] already. I don't know the official
> recommended workflows but I used to just push follow-up fixes.

It's at the bottom of the draft stack, so I think follow-ups would be
preferred.

> Excerpts from Stanislau Hlebik's message of 2017-02-07 00:52:13 -0800:
> > # HG changeset patch
> > # User Stanislau Hlebik <stash at fb.com>
> > # Date 1486457478 28800
> > #      Tue Feb 07 00:51:18 2017 -0800
> > # Node ID 8614d5d15d6fe47c3bcfdf79823f68f18c7741ae
> > # Parent  1f51b4658f21bbb797e922d155c1046eddccf91d
> > localrepo: avoid unnecessary conversion from node to rev
> > 
> > changelog.heads() first calls headrevs then converts them to nodes.
> > localrepo.heads() then sorts them using self.changelog.rev function and makes
> > useless conversion back to revs. Instead let's call changelog.headrevs() from
> > localrepo.heads(), sort the output and then convert to nodes. Because headrevs
> > does not support start parameter this optimization only works if start is None.
> > 
> > diff --git a/mercurial/localrepo.py b/mercurial/localrepo.py
> > --- a/mercurial/localrepo.py
> > +++ b/mercurial/localrepo.py
> > @@ -1852,6 +1852,10 @@
> >                                    listsubrepos)
> >  
> >      def heads(self, start=None):
> > +        if start is None:
> > +            headrevs = reversed(self.changelog.headrevs())
> > +            return [self.changelog.node(rev) for rev in headrevs]

Also, can you check if self.changelog has no visible cost? I'm a bit afraid that
this patch could actually made heads() slow because of repeated self.changelog
calls.