treemanifest: add walksubtrees api

Adds a new function to treemanifest that allows walking over the directories in
the tree. Currently it only accepts a matcher to prune the walk, but in the
future it will also accept a list of trees and will only walk over subtrees that
differ from the versions in the list. This will be useful for identifying what
parts of the tree are new to this revision, which is useful when deciding the
minimal set of trees to send to a client given that they have a certain tree
already.

Since this is intended for an extension to use, the only current consumer is a
test. In the future this function may be useful for implementing other
algorithms like diff and changegroup generation.

mercurial/manifest.py

@@ -1155,6 +1155,22 b' class treemanifest(object):'
                 subp1, subp2 = subp2, subp1
             writesubtree(subm, subp1, subp2)
 
+    def walksubtrees(self, matcher=None):
+        """Returns an iterator of the subtrees of this manifest, including this
+        manifest itself.
+
+        If `matcher` is provided, it only returns subtrees that match.
+        """
+        if matcher and not matcher.visitdir(self._dir[:-1] or '.'):
+            return
+        if not matcher or matcher(self._dir[:-1]):
+            yield self
+
+        self._load()
+        for d, subm in self._dirs.iteritems():
+            for subtree in subm.walksubtrees(matcher=matcher):
+                yield subtree
+
 class manifestrevlog(revlog.revlog):
     '''A revlog that stores manifest texts. This is responsible for caching the
     full-text manifest contents.

tests/test-manifest.py

@@ -467,5 +467,21 b' class testtreemanifest(unittest.TestCase'
     def parsemanifest(self, text):
         return manifestmod.treemanifest('', text)
 
+    def testWalkSubtrees(self):
+        m = self.parsemanifest(A_DEEPER_MANIFEST)
+
+        dirs = [s._dir for s in m.walksubtrees()]
+        self.assertEqual(
+            sorted(['', 'a/', 'a/c/', 'a/d/', 'a/b/', 'a/b/c/', 'a/b/d/']),
+            sorted(dirs)
+        )
+
+        match = matchmod.match('/', '', ['path:a/b/'])
+        dirs = [s._dir for s in m.walksubtrees(matcher=match)]
+        self.assertEqual(
+            sorted(['a/b/', 'a/b/c/', 'a/b/d/']),
+            sorted(dirs)
+        )
+
 if __name__ == '__main__':
     silenttestrunner.main(__name__)