phase: when phase cannot be reduced, hint at --force and return 1 (BC)

Before, trying to change the phase of a "public" node to "draft" would result
in:

  $ hg phase --draft .
  no phases changed
  [0]

With this patch:

  $ hg phase --draft .
  cannot move 1 changesets to a more permissive phase, use --force
  no phases changed
  [1]

On partial failures, the exit status is now 1 instead of 0 and the number of
changed nodes is displayed while it was only with --verbose. It seems useful to
tell the user that despite the apparent failure, something changed.

  $ hg phase --draft '5 or 7'
  cannot move 1 changesets to a more permissive phase, use --force
  phase changed for 1 changesets
  [1]

mercurial/commands.py

@@ -4210,7 +4210,8 b' def phase(ui, repo, *revs, **opts):'
 
         public < draft < secret
 
-    Return 0 on success, 1 if no phases were changed.
+    Return 0 on success, 1 if no phases were changed or some could not
+    be changed.
     """
     # search for a unique phase argument
     targetphase = None
@@ -4252,8 +4253,18 b' def phase(ui, repo, *revs, **opts):'
             changes = 0
             newdata = repo._phaserev
             changes = sum(o != newdata[i] for i, o in enumerate(olddata))
+            rejected = [n for n in nodes
+                        if newdata[repo[n].rev()] < targetphase]
+            if rejected:
+                ui.warn(_('cannot move %i changesets to a more permissive '
+                          'phase, use --force\n') % len(rejected))
+                ret = 1
             if changes:
-                ui.note(_('phase change for %i changesets\n') % changes)
+                msg = _('phase changed for %i changesets\n') % changes
+                if ret:
+                    ui.status(msg)
+                else:
+                    ui.note(msg)
             else:
                 ui.warn(_('no phases changed\n'))
                 ret = 1

tests/test-phases.t

@@ -402,3 +402,34 b' move changeset forward and backward'
   |
   o  0 public A
   
+test partial failure
+
+  $ hg phase --public 7
+  $ hg phase --draft '5 or 7'
+  cannot move 1 changesets to a more permissive phase, use --force
+  phase changed for 1 changesets
+  [1]
+  $ hg log -G --template "{rev} {phase} {desc}\n"
+  @    7 public merge B' and E
+  |\
+  | o  6 public B'
+  | |
+  +---o  5 draft H
+  | |
+  o |  4 public E
+  | |
+  o |  3 public D
+  | |
+  o |  2 public C
+  |/
+  o  1 public B
+  |
+  o  0 public A
+  
+
+test complete failure
+
+  $ hg phase --draft 7
+  cannot move 1 changesets to a more permissive phase, use --force
+  no phases changed
+  [1]