phases: return zero for no-op operations (issue4751) (BC)

It is rather unhelpful to return 1 if there were no changes because
the request matches the current state of phases. So we just undo that.

mercurial/commands.py

@@ -5025,8 +5025,7 b' def phase(ui, repo, *revs, **opts):'
 
         public < draft < secret
 
-    Returns 0 on success, 1 if no phases were changed or some could not
-    be changed.
+    Returns 0 on success, 1 if some phases could not be changed.
 
     (For more information about the phases concept, see :hg:`help phases`.)
     """
@@ -5095,7 +5094,6 b' def phase(ui, repo, *revs, **opts):'
                 ui.note(msg)
         else:
             ui.warn(_('no phases changed\n'))
-            ret = 1
     return ret
 
 def postincoming(ui, repo, modheads, optupdate, checkout):

tests/test-commandserver.t

@@ -322,7 +322,6 b' check that local configs for the cached '
   ...     runcommand(server, ['phase', '-r', '.'])
   *** runcommand phase -r . -p
   no phases changed
-   [1]
   *** runcommand commit -Am.
   *** runcommand rollback
   repository tip rolled back to revision 3 (undo commit)