localrepo: extract bookmarkheads method to bookmarks.py

This method is only used internally by destutil, and it's obscure
enough I'm willing to just move it without a deprecation warning,
especially since the new method has more constrained functionality.

Design-wise I'd also like to get active bookmark handling folded into
the bookmark store, so that we don't squirrel away an extra attribute
for the active bookmark on the repository object.

mercurial/bookmarks.py

@@ -226,6 +226,28 b' def deletedivergent(repo, deletefrom, bm'
                 deleted = True
     return deleted
 
+def headsforactive(repo):
+    """Given a repo with an active bookmark, return divergent bookmark nodes.
+
+    Args:
+      repo: A repository with an active bookmark.
+
+    Returns:
+      A list of binary node ids that is the full list of other
+      revisions with bookmarks divergent from the active bookmark. If
+      there were no divergent bookmarks, then this list will contain
+      only one entry.
+    """
+    if not repo._activebookmark:
+        raise ValueError(
+            'headsforactive() only makes sense with an active bookmark')
+    name = repo._activebookmark.split('@', 1)[0]
+    heads = []
+    for mark, n in repo._bookmarks.iteritems():
+        if mark.split('@', 1)[0] == name:
+            heads.append(n)
+    return heads
+
 def calculateupdate(ui, repo, checkout):
     '''Return a tuple (targetrev, movemarkfrom) indicating the rev to
     check out and where to move the active bookmark from, if needed.'''

mercurial/destutil.py

@@ -234,7 +234,7 b' msgdestmerge = {'
 def _destmergebook(repo, action='merge', sourceset=None, destspace=None):
     """find merge destination in the active bookmark case"""
     node = None
-    bmheads = repo.bookmarkheads(repo._activebookmark)
+    bmheads = bookmarks.headsforactive(repo)
     curhead = repo[repo._activebookmark].node()
     if len(bmheads) == 2:
         if curhead == bmheads[0]:
@@ -355,7 +355,7 b' def desthistedit(ui, repo):'
     return None
 
 def _statusotherbook(ui, repo):
-    bmheads = repo.bookmarkheads(repo._activebookmark)
+    bmheads = bookmarks.headsforactive(repo)
     curhead = repo[repo._activebookmark].node()
     if repo.revs('%n and parents()', curhead):
         # we are on the active bookmark

mercurial/localrepo.py

@@ -507,14 +507,6 b' class localrepository(object):'
     def _activebookmark(self):
         return self._bookmarks.active
 
-    def bookmarkheads(self, bookmark):
-        name = bookmark.split('@', 1)[0]
-        heads = []
-        for mark, n in self._bookmarks.iteritems():
-            if mark.split('@', 1)[0] == name:
-                heads.append(n)
-        return heads
-
     # _phaserevs and _phasesets depend on changelog. what we need is to
     # call _phasecache.invalidate() if '00changelog.i' was changed, but it
     # can't be easily expressed in filecache mechanism.