manifest: add matches() method

Move the code in context._manifestmatches() into a new
manifest.matches(). It's a natural place for the code to live and it
allows other callers to easily use it. It should also make it easier
to optimize the new method in alternative implementations of the
manifest (same reasoning as with manifest.diff()).

mercurial/context.py

@@ -71,19 +71,7 b' class basectx(object):'
         object oriented way for other contexts to customize the manifest
         generation.
         """
-        if match.always():
-            return self.manifest().copy()
-
-        files = match.files()
-        if (match.matchfn == match.exact or
-            (not match.anypats() and util.all(fn in self for fn in files))):
-            return self.manifest().intersectfiles(files)
-
-        mf = self.manifest().copy()
-        for fn in mf.keys():
-            if not match(fn):
-                del mf[fn]
-        return mf
+        return self.manifest().matches(match)
 
     def _matchstatus(self, other, match):
         """return match.always if match is none

mercurial/manifest.py

@@ -39,6 +39,22 b' class manifestdict(dict):'
                     ret._flags[fn] = flags
         return ret
 
+    def matches(self, match):
+        '''generate a new manifest filtered by the match argument'''
+        if match.always():
+            return self.copy()
+
+        files = match.files()
+        if (match.matchfn == match.exact or
+            (not match.anypats() and util.all(fn in self for fn in files))):
+            return self.intersectfiles(files)
+
+        mf = self.copy()
+        for fn in mf.keys():
+            if not match(fn):
+                del mf[fn]
+        return mf
+
     def diff(self, m2):
         '''Finds changes between the current manifest and m2. The result is
         returned as a dict with filename as key and values of the form