resolve: abort when not applicable (BC)

The resolve command is only relevant when mergestate is present.
This patch will make resolve abort when no mergestate is present.

This change will let people know when they are using resolve when they
shouldn't be. This change will let people know when their use of resolve
doesn't do anything.

Previously, |hg resolve -m| would allow mergestate to be created. This
patch now forbids that. Strictly speaking, this is backwards
incompatible. The author of this patch believes creating mergestate via
resolve doesn't make much sense and this side-effect was unintended.

mercurial/commands.py

@@ -4927,6 +4927,10 b' def resolve(ui, repo, *pats, **opts):'
                            'use --all to remerge all files'))
 
     ms = mergemod.mergestate(repo)
+
+    if not ms.active():
+        raise util.Abort(_('resolve command not applicable when not merging'))
+
     m = scmutil.match(repo[None], pats, opts)
     ret = 0
 

mercurial/merge.py

@@ -175,6 +175,18 b' class mergestate(object):'
                 raise
         return records
 
+    def active(self):
+        """Whether mergestate is active.
+
+        Returns True if there appears to be mergestate. This is a rough proxy
+        for "is a merge in progress."
+        """
+        # Check local variables before looking at filesystem for performance
+        # reasons.
+        return bool(self._local) or bool(self._state) or \
+               self._repo.opener.exists(self.statepathv1) or \
+               self._repo.opener.exists(self.statepathv2)
+
     def commit(self):
         """Write current state on disk (if necessary)"""
         if self._dirty:

tests/test-histedit-non-commute-abort.t

@@ -85,6 +85,8 b' abort the edit'
 
 log after abort
   $ hg resolve -l
+  abort: resolve command not applicable when not merging
+  [255]
   $ hg log --graph
   @  changeset:   6:bfa474341cc9
   |  tag:         tip

tests/test-resolve.t

@@ -37,9 +37,11 b' resolve the failure'
   $ hg resolve -m file
   $ hg commit -m 'resolved'
 
-resolve -l, should be empty
+resolve -l should error since no merge in progress
 
   $ hg resolve -l
+  abort: resolve command not applicable when not merging
+  [255]
 
 test crashed merge with empty mergestate
 

tests/test-shelve.t

@@ -262,6 +262,8 b' abort the unshelve and be happy'
   summary:     second
   
   $ hg resolve -l
+  abort: resolve command not applicable when not merging
+  [255]
   $ hg status
   A foo/foo
   ? a/a.orig