histedit: move topmost bookmark movement to a separate function

histedit treats topmost bookmark movement specially. The rest of the
bookmark movement could be handled by scmutil.cleanupnodes. So let's move
the special logic out to make the patch easier to review.

hgext/histedit.py

@@ -1541,21 +1541,30 b' def processreplacement(state):'
 
     return final, tmpnodes, new, newtopmost
 
+def movetopmostbookmarks(repo, oldtopmost, newtopmost):
+    """Move bookmark from oldtopmost to newly created topmost
+
+    This is arguably a feature and we may only want that for the active
+    bookmark. But the behavior is kept compatible with the old version for now.
+    """
+    if not oldtopmost or not newtopmost:
+        return
+    oldbmarks = repo.nodebookmarks(oldtopmost)
+    if oldbmarks:
+        with repo.lock(), repo.transaction('histedit') as tr:
+            marks = repo._bookmarks
+            for name in oldbmarks:
+                marks[name] = newtopmost
+            marks.recordchange(tr)
+
 def movebookmarks(ui, repo, mapping, oldtopmost, newtopmost):
     """Move bookmark from old to newly created node"""
     if not mapping:
         # if nothing got rewritten there is not purpose for this function
         return
+    movetopmostbookmarks(repo, oldtopmost, newtopmost)
     moves = []
     for bk, old in sorted(repo._bookmarks.iteritems()):
-        if old == oldtopmost:
-            # special case ensure bookmark stay on tip.
-            #
-            # This is arguably a feature and we may only want that for the
-            # active bookmark. But the behavior is kept compatible with the old
-            # version for now.
-            moves.append((bk, newtopmost))
-            continue
         base = old
         new = mapping.get(base, None)
         if new is None: