+ hg init
+ hg add a
+ hg ci -m a -d 0 0
+ hg add b
+ hg diff
diff -r 3903775176ed b
--- /dev/null
+++ b/b
@@ -0,0 +1,1 @@
+123
+ hg diff -r tip
diff -r 3903775176ed b
--- /dev/null
+++ b/b
@@ -0,0 +1,1 @@
+123