[PATCH 3 of 5 V2] treemanifest: make diff() faster

[Martin von Zweigbergk]

# HG changeset patch
# User Martin von Zweigbergk <martinvonz at google.com>
# Date 1424394815 28800
#      Thu Feb 19 17:13:35 2015 -0800
# Node ID f2b1de4e1c9b70a2f1f4298f61c3a60e38f4bfef
# Parent  a0311193e19703ea01890460d9abe1aa8421cad5
treemanifest: make diff() faster

Containment checking is slower in treemanifest than it is in
manifestdict, making the current diff algorithm O(n log n). By
traversing both treemanifests in parallel, we can make it O(n). More
importantly, once we start lazily loading submanifests, we will be
able to easily skip entire submanifest if they have the same nodeid.

diff -r a0311193e197 -r f2b1de4e1c9b mercurial/manifest.py
--- a/mercurial/manifest.py	Mon Feb 23 10:57:57 2015 -0800
+++ b/mercurial/manifest.py	Thu Feb 19 17:13:35 2015 -0800
@@ -527,25 +527,33 @@
         the nodeid will be None and the flags will be the empty
         string.
         '''
-        diff = {}
+        result = {}
+        emptytree = treemanifest()
+        def _diff(t1, t2):
+            for d, m1 in t1._dirs.iteritems():
+                m2 = t2._dirs.get(d, emptytree)
+                _diff(m1, m2)
 
-        for fn, n1 in self.iteritems():
-            fl1 = self.flags(fn)
-            n2 = m2.get(fn, None)
-            fl2 = m2.flags(fn)
-            if n2 is None:
-                fl2 = ''
-            if n1 != n2 or fl1 != fl2:
-                diff[fn] = ((n1, fl1), (n2, fl2))
-            elif clean:
-                diff[fn] = None
+            for d, m2 in t2._dirs.iteritems():
+                if d not in t1._dirs:
+                    _diff(emptytree, m2)
 
-        for fn, n2 in m2.iteritems():
-            if fn not in self:
-                fl2 = m2.flags(fn)
-                diff[fn] = ((None, ''), (n2, fl2))
+            for fn, n1 in t1._files.iteritems():
+                fl1 = t1._flags.get(fn, '')
+                n2 = t2._files.get(fn, None)
+                fl2 = t2._flags.get(fn, '')
+                if n1 != n2 or fl1 != fl2:
+                    result[t1._subpath(fn)] = ((n1, fl1), (n2, fl2))
+                elif clean:
+                    result[t1._subpath(fn)] = None
 
-        return diff
+            for fn, n2 in t2._files.iteritems():
+                if fn not in t1._files:
+                    fl2 = t2._flags.get(fn, '')
+                    result[t2._subpath(fn)] = ((None, ''), (n2, fl2))
+
+        _diff(self, m2)
+        return result
 
     def text(self):
         """Get the full data of this manifest as a bytestring."""