manifest: rewrite filesnotin to not make superfluous manifest copies

This also skips using diff() when all we care about is the filenames. I'm
expecting the built in set logic to be plenty fast. For really large manifests
with a matcher in play this should copy substantially less data around.

Differential Revision: https://phab.mercurial-scm.org/D8082

mercurial/manifest.py

@@ -23,6 +23,7 b' from .pycompat import getattr'
 from . import (
     encoding,
     error,
+    match as matchmod,
     mdiff,
     pathutil,
     policy,
@@ -482,17 +483,11 b' class manifestdict(object):'
 
     def filesnotin(self, m2, match=None):
         '''Set of files in this manifest that are not in the other'''
-        if match:
-            m1 = self.matches(match)
-            m2 = m2.matches(match)
-            return m1.filesnotin(m2)
-        diff = self.diff(m2)
-        files = set(
-            filepath
-            for filepath, hashflags in pycompat.iteritems(diff)
-            if hashflags[1][0] is None
-        )
-        return files
+        if match is not None:
+            match = matchmod.badmatch(match, lambda path, msg: None)
+            sm2 = set(m2.walk(match))
+            return {f for f in self.walk(match) if f not in sm2}
+        return {f for f in self if f not in m2}
 
     @propertycache
     def _dirs(self):