[PATCH 2 of 2] revset: fix merge() to fall back to changectx API if wdir specified

[Yuya Nishihara]

On Tue, 11 Jun 2019 00:04:19 +0200, Pierre-Yves David wrote:
> The patch looks functionnally good. Do we have any information on the
> performance impact ?

Appears no. IIRC, there are one (or two?) extra ops per loop to open
try-except context.

% echo 'merge()' | HGPLAIN=1 ./contrib/revsetbenchmarks.py --variants=plain -R ../mercurial '@:9b8e1a2d5b0c'
Revision:
0) Revision  69900:f163e2b2594c: phabricator: pass ui instead of repo to callconduit
1) Revision  69901:282376c97e4f: revset: use nullrev constant in merge()
2) Revision  (tip) 69903:9b8e1a2d5b0c: revset: fix merge() to fall back to changectx API if wdir specified


revset #0: merge()
   plain
0) 0.050687
1) 0.050049
2) 0.051622