[PATCH 3 of 3] revset: fast implementation for fullreposet.__and__

[Pierre-Yves David]

# HG changeset patch
# User Pierre-Yves David <pierre-yves.david at fb.com>
# Date 1398878911 25200
#      Wed Apr 30 10:28:31 2014 -0700
# Node ID f9806f19d2d158c228ae7207371afa42475ed946
# Parent  5aec2be794fbd94adc4f624c57cdd2fc9907e6e3
revset: fast implementation for fullreposet.__and__

"And" operation with something that contains the whole repo should be super
cheap. Check method docstring for details.

This provide massive boost to simple revset that use `subset & xxx`

revset #0: p1(20000)
0) wall 0.002447 comb 0.010000 user 0.010000 sys 0.000000 (best of 767)
1) wall 0.000529 comb 0.000000 user 0.000000 sys 0.000000 (best of 3947)

revset #1: p2(10000)
0) wall 0.002464 comb 0.000000 user 0.000000 sys 0.000000 (best of 913)
1) wall 0.000530 comb 0.000000 user 0.000000 sys 0.000000 (best of 4226)

No other regression spotted.

More performance are expected  in the future as more revset predicate are
converted to use `subset & xxx`

diff --git a/mercurial/revset.py b/mercurial/revset.py
--- a/mercurial/revset.py
+++ b/mercurial/revset.py
@@ -2865,7 +2865,29 @@ class fullreposet(_spanset):
     """
 
     def __init__(self, repo):
         super(fullreposet, self).__init__(repo)
 
+    def __and__(self, other):
+        """fullrepo & other -> other
+
+        As self contains the whole repo, all of the other set should also be in
+        self. Therefor `self & other = other`.
+
+        This boldly assume the other contains valid revs only.
+        """
+        # dif not a smartset, make is so
+        if not util.safehasattr(other, 'set'):
+            other = baseset(other)
+
+        # preserve order:
+        #
+        # this is probably useless and harmful in multiple case but this match
+        # the current behavior.
+        if self.isascending():
+            other.ascending()
+        else:
+            other.descending()
+        return other
+
 # tell hggettext to extract docstrings from these functions:
 i18nfunctions = symbols.values()