export: export working directory parent by default

A common usecase for export is to preview the patch that will be patchbombed or
to see what changed in a revision found by bisect. Showing the working
directory parent is thus a useful and obvious default.

mercurial/commands.py

@@ -2709,11 +2709,12 b' def diff(ui, repo, *pats, **opts):'
     ('', 'switch-parent', None, _('diff against the second parent')),
     ('r', 'rev', [], _('revisions to export'), _('REV')),
     ] + diffopts,
-    _('[OPTION]... [-o OUTFILESPEC] [-r] REV...'))
+    _('[OPTION]... [-o OUTFILESPEC] [-r] [REV]...'))
 def export(ui, repo, *changesets, **opts):
     """dump the header and diffs for one or more changesets
 
     Print the changeset header and diffs for one or more revisions.
+    If no revision is given, the parent of the working directory is used.
 
     The information shown in the changeset header is: author, date,
     branch name (if non-default), changeset hash, parent(s) and commit
@@ -2769,6 +2770,8 b' def export(ui, repo, *changesets, **opts'
     Returns 0 on success.
     """
     changesets += tuple(opts.get('rev', []))
+    if not changesets:
+        changesets = ['.']
     revs = scmutil.revrange(repo, changesets)
     if not revs:
         raise util.Abort(_("export requires at least one changeset"))

tests/test-export.t

@@ -148,8 +148,23 b' Checking if only alphanumeric characters'
 Catch exporting unknown revisions (especially empty revsets, see issue3353)
 
   $ hg export
-  abort: export requires at least one changeset
-  [255]
+  # HG changeset patch
+  # User test
+  # Date 0 0
+  #      Thu Jan 01 00:00:00 1970 +0000
+  # Node ID 197ecd81a57f760b54f34a58817ad5b04991fa47
+  # Parent  f3acbafac161ec68f1598af38f794f28847ca5d3
+   !"#$%&(,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\]^_`abcdefghijklmnopqrstuvwxyz{|}~
+  
+  diff -r f3acbafac161 -r 197ecd81a57f foo
+  --- a/foo	Thu Jan 01 00:00:00 1970 +0000
+  +++ b/foo	Thu Jan 01 00:00:00 1970 +0000
+  @@ -10,3 +10,4 @@
+   foo-9
+   foo-10
+   foo-11
+  +line
+
   $ hg export ""
   hg: parse error: empty query
   [255]