# HG changeset patch
# User Lucas Moscovicz <lmoscovicz@fb.com>
# Date 1391534085 28800
# Node ID 51890507c6b3be0b24afffaedd77a8ecd523ac9c
# Parent  8dabcc889e3329ff3c5f2cbd4eda859a7712124c
revset: added lazyset implementation to matching revset

Performance Benchmarking:

$ time hg log -qr "first(matching(0))"
0:9117c6561b0b

real  0m2.213s
user  0m2.149s
sys 0m0.055s

$ time ./hg log -qr "first(matching(0))"
0:9117c6561b0b

real  0m0.177s
user  0m0.137s
sys 0m0.038s

diff -r 8dabcc889e33 -r 51890507c6b3 mercurial/revset.py
--- a/mercurial/revset.py	Tue Feb 04 08:51:07 2014 -0800
+++ b/mercurial/revset.py	Tue Feb 04 09:14:45 2014 -0800
@@ -1365,18 +1365,18 @@
     # is only one field to match)
     getinfo = lambda r: [f(r) for f in getfieldfuncs]
 
-    matches = set()
-    for rev in revs:
-        target = getinfo(rev)
-        for r in subset:
+    def matches(x):
+        for rev in revs:
+            target = getinfo(rev)
             match = True
             for n, f in enumerate(getfieldfuncs):
-                if target[n] != f(r):
+                if target[n] != f(x):
                     match = False
-                    break
             if match:
-                matches.add(r)
-    return baseset([r for r in subset if r in matches])
+                return True
+        return False
+
+    return lazyset(subset, matches)
 
 def reverse(repo, subset, x):
     """``reverse(set)``