[PATCH 2 of 2] cat: do not instantiate subrepo if no potential match in it

[Yuya Nishihara]

On Sat, 25 Nov 2017 23:53:45 -0500, Matt Harbison wrote:
> On Sat, 25 Nov 2017 02:35:04 -0500, Yuya Nishihara <yuya at tcha.org> wrote:
> 
> > # HG changeset patch
> > # User Yuya Nishihara <yuya at tcha.org>
> > # Date 1511593310 -32400
> > #      Sat Nov 25 16:01:50 2017 +0900
> > # Node ID b6e526ee5d2662ca30a555ca51264b3e371fe44e
> > # Parent  38e952030f0c4746257280d47f0f94b6cb9ddb41
> > cat: do not instantiate subrepo if no potential match in it
> >
> > This fixes the test failure in hg-git.
> >
> > https://bitbucket.org/durin42/hg-git/issues/227/
> >
> > diff --git a/mercurial/cmdutil.py b/mercurial/cmdutil.py
> > --- a/mercurial/cmdutil.py
> > +++ b/mercurial/cmdutil.py
> > @@ -3068,6 +3068,8 @@ def cat(ui, repo, ctx, matcher, basefm,
> >          err = 0
> >     for subpath in sorted(ctx.substate):
> > +        if not matcher.visitdir(subpath):
> > +            continue
> 
> The basematcher contract says the result is undefined if False is returned  
> for any parent directory.  Do we need a subrepo utility method to break up  
> the subpath and test top down?  Consider 'directory/subrepo', where  
> 'directory' is excluded.

(+CC Martin)

Yeah the doc says that, but not all callers seem to obey the restriction. So
I take it visitdir() won't return Falsy value if there is a possible match,
even though it might return non-False for Falsy case if any parents return
False.

> It's probably beyond the scope of what you were fixing, but should all  
> subrepo recursion be guarded like this?
> 
> >          sub = ctx.sub(subpath)
> >          try:
> >              submatch = matchmod.subdirmatcher(subpath, matcher)

Maybe we'll need ctx.walksub(matcher) which yields (subrepo, submatcher) pairs?