[PATCH 2 of 2 V3] manifest: change manifestctx to not inherit from manifestdict

[Durham Goode]

# HG changeset patch
# User Durham Goode <durham at fb.com>
# Date 1473702943 25200
#      Mon Sep 12 10:55:43 2016 -0700
# Node ID 1bbdc6966b8fc477538e0a41cafaf07debb0fa05
# Parent  0570e4b415b5814633cfe1f66b88f487c08cfa17
manifest: change manifestctx to not inherit from manifestdict

If manifestctx inherits from manifestdict, it requires some weird logic to
lazily load the dict if a piece of information is asked for. This ended up being
complicated and unintuitive to use.

Let's move the dict creation to .read(). This will make even more sense once we
start adding readdelta() and other similar methods to manifestctx.

diff --git a/mercurial/context.py b/mercurial/context.py
--- a/mercurial/context.py
+++ b/mercurial/context.py
@@ -528,7 +528,7 @@ class changectx(basectx):
 
     @propertycache
     def _manifest(self):
-        return self._repo.manifestlog[self._changeset.manifest]
+        return self._repo.manifestlog[self._changeset.manifest].read()
 
     @propertycache
     def _manifestdelta(self):
diff --git a/mercurial/manifest.py b/mercurial/manifest.py
--- a/mercurial/manifest.py
+++ b/mercurial/manifest.py
@@ -962,12 +962,13 @@ class manifestlog(object):
             self._mancache[node] = m
         return m
 
-class manifestctx(manifestdict):
+class manifestctx(object):
     """A class representing a single revision of a manifest, including its
     contents, its parent revs, and its linkrev.
     """
     def __init__(self, revlog, node):
         self._revlog = revlog
+        self._data = None
 
         self._node = node
 
@@ -978,21 +979,26 @@ class manifestctx(manifestdict):
         #rev = revlog.rev(node)
         #self.linkrev = revlog.linkrev(rev)
 
-        # This should eventually be made lazy loaded, so consumers can access
-        # the node/p1/linkrev data without having to parse the whole manifest.
-        data = revlog.revision(node)
-        arraytext = array.array('c', data)
-        revlog._fulltextcache[node] = arraytext
-        super(manifestctx, self).__init__(data)
-
     def node(self):
         return self._node
 
-class treemanifestctx(treemanifest):
+    def read(self):
+        if not self._data:
+            if self._node == revlog.nullid:
+                self._data = manifestdict()
+            else:
+                text = self._revlog.revision(self._node)
+                arraytext = array.array('c', text)
+                self._revlog._fulltextcache[self._node] = arraytext
+                self._data = manifestdict(text)
+        return self._data
+
+class treemanifestctx(object):
     def __init__(self, revlog, dir, node):
         revlog = revlog.dirlog(dir)
         self._revlog = revlog
         self._dir = dir
+        self._data = None
 
         self._node = node
 
@@ -1003,19 +1009,26 @@ class treemanifestctx(treemanifest):
         #rev = revlog.rev(node)
         #self.linkrev = revlog.linkrev(rev)
 
-        if revlog._treeondisk:
-            super(treemanifestctx, self).__init__(dir=dir)
-            def gettext():
-                return revlog.revision(node)
-            def readsubtree(dir, subm):
-                return revlog.dirlog(dir).read(subm)
-            self.read(gettext, readsubtree)
-            self.setnode(node)
-        else:
-            text = revlog.revision(node)
-            arraytext = array.array('c', text)
-            revlog.fulltextcache[node] = arraytext
-            super(treemanifestctx, self).__init__(dir=dir, text=text)
+    def read(self):
+        if not self._data:
+            if self._node == revlog.nullid:
+                self._data = treemanifest()
+            elif self._revlog._treeondisk:
+                m = treemanifest(dir=self._dir)
+                def gettext():
+                    return self._revlog.revision(self._node)
+                def readsubtree(dir, subm):
+                    return treemanifestctx(self._revlog, dir, subm).read()
+                m.read(gettext, readsubtree)
+                m.setnode(self._node)
+                self._data = m
+            else:
+                text = self._revlog.revision(self._node)
+                arraytext = array.array('c', text)
+                self._revlog.fulltextcache[self._node] = arraytext
+                self._data = treemanifest(dir=self._dir, text=text)
+
+        return self._data
 
     def node(self):
         return self._node
@@ -1133,7 +1146,7 @@ class manifest(manifestrevlog):
             cached = self._mancache[node]
             if (isinstance(cached, manifestctx) or
                 isinstance(cached, treemanifestctx)):
-                cached = cached
+                cached = cached.read()
             return cached
         if self._treeondisk:
             def gettext():