[PATCH] revset: for x^2, do not take null as a valid p2 revision

[Pierre-Yves David]

On 10/15/2016 09:06 AM, Yuya Nishihara wrote:
> 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 <yuya at 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.

I've pushed this as a net improvement.

>>> 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?
>
> 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.

I remember a discussion about having the special revision excluded 
unless something else in the revset make a direct reference to it. But 
this is a discussion for after this cycle.

Cheers,

-- 
Pierre-Yves David