diff: deprecate -r option

The new `--from`/`--to` options should be enough to support all the
uses cases and are easier to understand, so there is no reason that
I'm aware of to use `-r` anymore.

Differential Revision: https://phab.mercurial-scm.org/D9564

mercurial/commands.py

@@ -2455,7 +2455,7 b" def debugcomplete(ui, cmd=b'', **opts):"
 @command(
     b'diff',
     [
-        (b'r', b'rev', [], _(b'revision'), _(b'REV')),
+        (b'r', b'rev', [], _(b'revision (DEPRECATED)'), _(b'REV')),
         (b'', b'from', b'', _(b'revision to diff from'), _(b'REV1')),
         (b'', b'to', b'', _(b'revision to diff to'), _(b'REV2')),
         (b'c', b'change', b'', _(b'change made by revision'), _(b'REV')),

relnotes/next

@@ -21,7 +21,8 b''
    debugstrip`. The extension remains for compatibility.
 
  * `hg diff` now supports `--from <rev>` and `--to <rev>` arguments as
-   clearer alternatives to `-r <revs>`.
+   clearer alternatives to `-r <revs>`. `-r <revs>` has been
+   deprecated.
 
  * The memory footprint per changeset during pull/unbundle
    operations has been further reduced.

tests/test-help.t

@@ -665,7 +665,6 b' Test command without options'
   
   options ([+] can be repeated):
   
-   -r --rev REV [+]         revision
       --from REV1           revision to diff from
       --to REV2             revision to diff to
    -c --change REV          change made by revision