commit: make the error message more specific while aborting branch closing

Differential Revision: https://phab.mercurial-scm.org/D6493

mercurial/commands.py

@@ -1677,7 +1677,7 b' def _docommit(ui, repo, *pats, **opts):'
             raise error.Abort(_('current revision is already a branch closing'
                                 ' head'))
         elif not bheads:
-            raise error.Abort(_('can only close branch heads'))
+            raise error.Abort(_('branch "%s" has no heads to close') % branch)
         elif branch == repo['.'].branch() and repo['.'].node() not in bheads:
             raise error.Abort(_('can only close branch heads'))
         elif opts.get('amend'):

tests/test-commit-amend.t

@@ -892,7 +892,7 b' This silliness fails:'
   marked working directory as branch silliness
   $ echo b >> b
   $ hg ci --close-branch -m'open and close'
-  abort: can only close branch heads
+  abort: branch "silliness" has no heads to close
   [255]
 
 Test that amend with --secret creates new secret changeset forcibly