$ hg init a
$ cd a
$ hg diff inexistent1 inexistent2
inexistent1: No such file or directory
inexistent2: No such file or directory
$ echo bar > foo
$ hg add foo
$ hg ci -m 'add foo' -d '1000000 0'
$ echo foobar > foo
$ hg ci -m 'change foo' -d '1000001 0'
$ hg --quiet diff -r 0 -r 1
--- a/foo Mon Jan 12 13:46:40 1970 +0000
+++ b/foo Mon Jan 12 13:46:41 1970 +0000
@@ -1,1 +1,1 @@
-bar
+foobar
$ hg diff -r 0 -r 1
diff -r 74de3f1392e2 -r b8b5f023a6ad foo
--- a/foo Mon Jan 12 13:46:40 1970 +0000
+++ b/foo Mon Jan 12 13:46:41 1970 +0000
@@ -1,1 +1,1 @@
-bar
+foobar
$ hg --verbose diff -r 0 -r 1
diff -r 74de3f1392e2 -r b8b5f023a6ad foo
--- a/foo Mon Jan 12 13:46:40 1970 +0000
+++ b/foo Mon Jan 12 13:46:41 1970 +0000
@@ -1,1 +1,1 @@
-bar
+foobar
$ hg --debug diff -r 0 -r 1
diff -r 74de3f1392e2d67856fb155963441f2610494e1a -r b8b5f023a6ad77fc378bd95cf3fa00cd1414d107 foo
--- a/foo Mon Jan 12 13:46:40 1970 +0000
+++ b/foo Mon Jan 12 13:46:41 1970 +0000
@@ -1,1 +1,1 @@
-bar
+foobar