diff -r c2a81aa19980 -r 97b2f26dfc43 tests/test-revset.t
--- a/tests/test-revset.t	Fri Mar 28 16:12:05 2014 -0700
+++ b/tests/test-revset.t	Thu Mar 20 18:44:25 2014 -0700
@@ -744,6 +744,43 @@
   6
   7
 
+test usage in revpair (with "+")
+
+(real pair)
+
+  $ hg diff -r 'tip^^' -r 'tip'
+  diff -r 2326846efdab -r 24286f4ae135 .hgtags
+  --- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+  +++ b/.hgtags	Thu Jan 01 00:00:00 1970 +0000
+  @@ -0,0 +1,1 @@
+  +e0cc66ef77e8b6f711815af4e001a6594fde3ba5 1.0
+  $ hg diff -r 'tip^^::tip'
+  diff -r 2326846efdab -r 24286f4ae135 .hgtags
+  --- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+  +++ b/.hgtags	Thu Jan 01 00:00:00 1970 +0000
+  @@ -0,0 +1,1 @@
+  +e0cc66ef77e8b6f711815af4e001a6594fde3ba5 1.0
+
+(single rev)
+
+  $ hg diff -r 'tip^' -r 'tip^'
+  $ hg diff -r 'tip^::tip^ or tip^'
+
+(single rev that does not looks like a range)
+
+  $ hg diff -r 'tip^ or tip^'
+  diff -r d5d0dcbdc4d9 .hgtags
+  --- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+  +++ b/.hgtags	* (glob)
+  @@ -0,0 +1,1 @@
+  +e0cc66ef77e8b6f711815af4e001a6594fde3ba5 1.0
+
+(no rev)
+
+  $ hg diff -r 'author("babar") or author("celeste")'
+  abort: empty revision range
+  [255]
+
 aliases:
 
   $ echo '[revsetalias]' >> .hg/hgrc