[PATCH 3 of 3 V2] dirstate._walkexplicit: don't bother normalizing '.'

[Siddharth Agarwal]

# HG changeset patch
# User Siddharth Agarwal <sid0 at fb.com>
# Date 1427678928 25200
#      Sun Mar 29 18:28:48 2015 -0700
# Node ID 64ded2aa226dbe1d2e1f96ec476d707cabe8e56e
# Parent  a05be84438fb2a502590b7ae7d5001308b558c03
dirstate._walkexplicit: don't bother normalizing '.'

The overwhelmingly common case is running commands like 'hg diff' with no
arguments. Therefore the only file that'll be listed is the root directory.
Normalizing that's just a waste of time.

This means that for a plain 'hg diff' we'll never need to construct the
foldmap, saving us a significant chunk of time.

On case-insensitive HFS+ on OS X, for a large repository with over 200,000
files, this brings down 'hg diff' from 2.97 seconds to 2.36.

diff --git a/mercurial/dirstate.py b/mercurial/dirstate.py
--- a/mercurial/dirstate.py
+++ b/mercurial/dirstate.py
@@ -634,7 +634,9 @@
 
         alldirs = None
         for ff in files:
-            if normalize:
+            # constructing the foldmap is expensive, so don't do it for the
+            # common case where files is ['.']
+            if normalize and ff != '.':
                 nf = normalize(ff, False, True)
             else:
                 nf = ff