$ hg init

  $ touch a

  $ hg add a

  $ hg ci -m "a"

  $ echo 123 > b

  $ hg add b

  $ hg diff --nodates

  diff -r 3903775176ed b

  --- /dev/null

  +++ b/b

  @@ -0,0 +1,1 @@

  +123

  $ hg diff --nodates -r tip

  diff -r 3903775176ed b

  --- /dev/null

  +++ b/b

  @@ -0,0 +1,1 @@

  +123

  $ echo foo > a

  $ hg diff --nodates

  diff -r 3903775176ed a

  --- a/a

  +++ b/a

  @@ -0,0 +1,1 @@

  +foo

  diff -r 3903775176ed b

  --- /dev/null

  +++ b/b

  @@ -0,0 +1,1 @@

  +123

  $ hg diff -r ""

  hg: parse error: empty query

  [255]

  $ hg diff -r tip -r ""

  hg: parse error: empty query

  [255]

Remove a file that was added via merge. Since the file is not in parent 1,

it should not be in the diff.

  $ hg ci -m 'a=foo' a

  $ hg co -Cq null

  $ echo 123 > b

  $ hg add b

  $ hg ci -m "b"

  created new head

  $ hg merge 1

  1 files updated, 0 files merged, 0 files removed, 0 files unresolved

  (branch merge, don't forget to commit)

  $ hg rm -f a

  $ hg diff --nodates

Rename a file that was added via merge. Since the rename source is not in

parent 1, the diff should be relative to /dev/null

  $ hg co -Cq 2

  $ hg merge 1

  1 files updated, 0 files merged, 0 files removed, 0 files unresolved

  (branch merge, don't forget to commit)

  $ hg mv a a2

  $ hg diff --nodates

  diff -r cf44b38435e5 a2

  --- /dev/null

  +++ b/a2

  @@ -0,0 +1,1 @@

  +foo

  $ hg diff --nodates --git

  diff --git a/a2 b/a2

  new file mode 100644

  --- /dev/null

  +++ b/a2

  @@ -0,0 +1,1 @@

  +foo