[PATCH] log: make file log slow path usable on large repos

[Durham Goode]

# HG changeset patch
# User Durham Goode <durham at fb.com>
# Date 1378867774 25200
#      Tue Sep 10 19:49:34 2013 -0700
# Node ID 73303bff81aaa188c0113791f0147f9e13a9eef8
# Parent  c821473150d2cc0c75c74a0292e9a060eb19bc36
log: make file log slow path usable on large repos

Running "hg log <pattern or directory>" on large repos took a very, very long
time because it first read ctx.files() for every commit before even starting to
process the results.

This change makes the ctx.files() check lazy, which makes the command start
producing results immediately.

diff --git a/mercurial/cmdutil.py b/mercurial/cmdutil.py
--- a/mercurial/cmdutil.py
+++ b/mercurial/cmdutil.py
@@ -1172,12 +1172,34 @@
                                'filenames'))
 
         # The slow path checks files modified in every changeset.
-        for i in sorted(revs):
-            ctx = change(i)
-            matches = filter(match, ctx.files())
-            if matches:
-                fncache[i] = matches
-                wanted.add(i)
+        # This is really slow on large repos, so compute the set lazily.
+        class lazywantedset(object):
+            def __init__(self):
+                self.set = set()
+                self.revs = set(revs)
+
+            # No need to worry about locality here because it will be accessed
+            # in the same order as the increasing window below.
+            def __contains__(self, value):
+                if value in self.set:
+                    return True
+                elif not value in self.revs:
+                    return False
+                else:
+                    self.revs.discard(value)
+                    ctx = change(value)
+                    matches = filter(match, ctx.files())
+                    if matches:
+                        fncache[value] = matches
+                        self.set.add(value)
+                        return True
+                    return False
+
+            def discard(self, value):
+                self.revs.discard(value)
+                self.set.discard(value)
+
+        wanted = lazywantedset()
 
     class followfilter(object):
         def __init__(self, onlyfirst=False):