On Fri, 14 Oct 2016 18:42:12 +0200, Pierre-Yves David wrote:
> On 10/14/2016 05:35 PM, Yuya Nishihara wrote:
> > # HG changeset patch
> > # User Yuya Nishihara <y...@tcha.org>
> > # Date 1476455580 -32400
> > # Fri Oct 14 23:33:00 2016 +0900
> > # Node ID 18ba0036dd81db9e45fd1a450c7f207f1b89f22c
> > # Parent 5cb830801855dbb63e98b948e355bc995d295bf3
> > revset: for x^2, do not take null as a valid p2 revision
> >
> > Since we don't count null p2 revision as a parent, x^2 should never return
> > null even if null is explicitly populated.
> >
> > diff --git a/mercurial/revset.py b/mercurial/revset.py
> > --- a/mercurial/revset.py
> > +++ b/mercurial/revset.py
> > @@ -1620,7 +1620,7 @@ def parentspec(repo, subset, x, n, order
> > ps.add(cl.parentrevs(r)[0])
> > elif n == 2:
> > parents = cl.parentrevs(r)
> > - if len(parents) > 1:
> > + if parents[1] != node.nullrev:
>
> Is there any chance that p1 is nullid and p2 is not?

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No.
> Also, how does this behave if r is a root (p1 and p2 is nullid).
>
> Should we instead filter the parents list ?::
>
> parents = [p for p in cl.parentrevs(r) if p != nullrev]
IMHO, that's undecided problem. It doesn't make sense to take p2=null as
a valid relation because otherwise all revisions must be rooted to null (b),
which doesn't agree with how we draw a graph including null (a).
(a) -1 - 0 - 1 ...
(b) -1 = 0 - 1
\ /
------
But we could say '0^1' (or 'null:tip & 0^1') is null per the graph (a). So
I fixed only 'x^2 -> null', which is clearly wrong.
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