--- a/mercurial/context.py	Sun May 06 14:15:17 2012 -0500
+++ b/mercurial/context.py	Sun May 06 14:20:53 2012 -0500
@@ -645,9 +645,16 @@
         # the easy case: no (relevant) renames
         if fc2.path() == self.path() and self.path() in actx:
             return actx[self.path()]
-        acache = {}
+
+        # the next easiest cases: unambiguous predecessor (name trumps
+        # history)
+        if self.path() in actx and fc2.path() not in actx:
+            return actx[self.path()]
+        if fc2.path() in actx and self.path() not in actx:
+            return actx[fc2.path()]
 
         # prime the ancestor cache for the working directory
+        acache = {}
         for c in (self, fc2):
             if c._filerev is None:
                 pl = [(n.path(), n.filenode()) for n in c.parents()]

--- a/tests/test-graft.t	Sun May 06 14:15:17 2012 -0500
+++ b/tests/test-graft.t	Sun May 06 14:20:53 2012 -0500
@@ -72,28 +72,23 @@
   # HG changeset patch
   # User foo
   # Date 0 0
-  # Node ID d2e44c99fd3f31c176ea4efb9eca9f6306c81756
+  # Node ID ef0ef43d49e79e81ddafdc7997401ba0041efc82
   # Parent  68795b066622ca79a25816a662041d8f78f3cd9e
   2
   
   diff --git a/a b/b
   rename from a
   rename to b
-  --- a/a
-  +++ b/b
-  @@ -1,1 +1,1 @@
-  -a
-  +b
 
 Look for extra:source
 
   $ hg log --debug -r tip
-  changeset:   7:d2e44c99fd3f31c176ea4efb9eca9f6306c81756
+  changeset:   7:ef0ef43d49e79e81ddafdc7997401ba0041efc82
   tag:         tip
   phase:       draft
   parent:      0:68795b066622ca79a25816a662041d8f78f3cd9e
   parent:      -1:0000000000000000000000000000000000000000
-  manifest:    7:5d59766436fd8fbcd38e7bebef0f6eaf3eebe637
+  manifest:    7:e59b6b228f9cbf9903d5e9abf996e083a1f533eb
   user:        foo
   date:        Thu Jan 01 00:00:00 1970 +0000
   files+:      b
@@ -128,16 +123,20 @@
     checking for directory renames
   resolving manifests
    overwrite: False, partial: False
-   ancestor: 68795b066622, local: d2e44c99fd3f+, remote: 5d205f8b35b6
+   ancestor: 68795b066622, local: ef0ef43d49e7+, remote: 5d205f8b35b6
    b: local copied/moved to a -> m
   preserving b for resolve of b
   updating: b 1/1 files (100.00%)
-  graft for revision 1 is empty
+  picked tool 'internal:merge' for b (binary False symlink False)
+  merging b and a to b
+  my b@ef0ef43d49e7+ other a@5d205f8b35b6 ancestor a@68795b066622
+   premerge successful
+  b
   grafting revision 5
     searching for copies back to rev 1
   resolving manifests
    overwrite: False, partial: False
-   ancestor: 4c60f11aa304, local: d2e44c99fd3f+, remote: 97f8bfe72746
+   ancestor: 4c60f11aa304, local: 6b9e5368ca4e+, remote: 97f8bfe72746
    e: remote is newer -> g
   updating: e 1/1 files (100.00%)
   getting e
@@ -146,7 +145,7 @@
     searching for copies back to rev 1
   resolving manifests
    overwrite: False, partial: False
-   ancestor: 4c60f11aa304, local: 839a7e8fcf80+, remote: 9c233e8e184d
+   ancestor: 4c60f11aa304, local: 1905859650ec+, remote: 9c233e8e184d
    e: versions differ -> m
    d: remote is newer -> g
   preserving e for resolve of e
@@ -155,7 +154,7 @@
   updating: e 2/2 files (100.00%)
   picked tool 'internal:merge' for e (binary False symlink False)
   merging e
-  my e@839a7e8fcf80+ other e@9c233e8e184d ancestor e@68795b066622
+  my e@1905859650ec+ other e@9c233e8e184d ancestor e@68795b066622
   warning: conflicts during merge.
   merging e incomplete! (edit conflicts, then use 'hg resolve --mark')
   abort: unresolved conflicts, can't continue
@@ -201,11 +200,13 @@
 View graph:
 
   $ hg --config extensions.graphlog= log -G --template '{author}@{rev}.{phase}: {desc}\n'
-  @  test@10.draft: 3
+  @  test@11.draft: 3
+  |
+  o  test@10.draft: 4
   |
-  o  test@9.draft: 4
+  o  test@9.draft: 5
   |
-  o  test@8.draft: 5
+  o  bar@8.draft: 1
   |
   o  foo@7.draft: 2
   |
@@ -233,17 +234,17 @@
   grafting revision 7
 
   $ hg log -r 7 --template '{rev}:{node}\n'
-  7:d2e44c99fd3f31c176ea4efb9eca9f6306c81756
+  7:ef0ef43d49e79e81ddafdc7997401ba0041efc82
   $ hg log -r 2 --template '{rev}:{node}\n'
   2:5c095ad7e90f871700f02dd1fa5012cb4498a2d4
 
   $ hg log --debug -r tip
-  changeset:   12:95adbe5de6b10f376b699ece9ed5a57cd7b4b0f6
+  changeset:   13:9db0f28fd3747e92c57d015f53b5593aeec53c2d
   tag:         tip
   phase:       draft
-  parent:      11:b592ea63bb0c19a6c5c44685ee29a2284f9f1b8f
+  parent:      12:b592ea63bb0c19a6c5c44685ee29a2284f9f1b8f
   parent:      -1:0000000000000000000000000000000000000000
-  manifest:    12:9944044f82a462bbaccc9bdf7e0ac5b811db7d1b
+  manifest:    13:dc313617b8c32457c0d589e0dbbedfe71f3cd637
   user:        foo
   date:        Thu Jan 01 00:00:00 1970 +0000
   files+:      b
@@ -261,7 +262,7 @@
   [255]
 
 Disallow grafting already grafted csets with the same origin onto each other
-  $ hg up -q 12
+  $ hg up -q 13
   $ hg graft 2
   skipping already grafted revision 2
   [255]
@@ -274,5 +275,5 @@
   skipping already grafted revision 2
   [255]
   $ hg graft tip
-  skipping already grafted revision 12 (same origin 2)
+  skipping already grafted revision 13 (same origin 2)
   [255]