[PATCH 4 of 8 RFC] basectx: cache filectx generation for all contexts

[Sean Farley]

# HG changeset patch
# User Sean Farley <sean.michael.farley at gmail.com>
# Date 1403899852 18000
#      Fri Jun 27 15:10:52 2014 -0500
# Node ID 6f2891408ace48a633862fd2b3dfb0ade1ab99db
# Parent  124225c16d40a0c2707e346c67e2a7a332ca0509
basectx: cache filectx generation for all contexts

Previously, filecontexts are generated on the fly but not cached. We need to
keep them around if we're going to allow the data inside to be changed.

diff --git a/mercurial/context.py b/mercurial/context.py
--- a/mercurial/context.py
+++ b/mercurial/context.py
@@ -31,10 +31,11 @@ class basectx(object):
         o = super(basectx, cls).__new__(cls)
 
         o._repo = repo
         o._rev = nullrev
         o._node = nullid
+        o._filectxs = {}
 
         return o
 
     def __str__(self):
         return short(self.node())
@@ -56,11 +57,17 @@ class basectx(object):
 
     def __contains__(self, key):
         return key in self._manifest
 
     def __getitem__(self, key):
-        return self.filectx(key)
+        try:
+            return self._filectxs[key]
+        except KeyError:
+            v = self.filectx(key)
+            self._filectxs[key] = v
+            return v
+
 
     def __iter__(self):
         for f in sorted(self._manifest):
             yield f