# HG changeset patch
# User Pierre-Yves David <pierre-yves.david@fb.com>
# Date 2014-09-17 17:59:52
# Node ID a428db9ab61ddd870983eda1e0bf4d328c7b32c0
# Parent  bbf4f3dfd700256f186315d2996b74fe1ccae370

revset: use `subset &` in bare `p1()`

This takes advantage of the `fullreposet` smartness and yields a nice
speedup.

revset #0: p1()
0) wall 0.003256 comb 0.010000 user 0.010000 sys 0.000000 (best of 527)
1) wall 0.000066 comb 0.000000 user 0.000000 sys 0.000000 (best of 23224)

diff --git a/mercurial/revset.py b/mercurial/revset.py
--- a/mercurial/revset.py
+++ b/mercurial/revset.py
@@ -1198,7 +1198,9 @@ def p1(repo, subset, x):
     """
     if x is None:
         p = repo[x].p1().rev()
-        return subset.filter(lambda r: r == p)
+        if p >= 0:
+            return subset & baseset([p])
+        return baseset([])
 
     ps = set()
     cl = repo.changelog