treemanifests: store whether a lazydirs entry needs copied after materializing

Due to the way that things like manifestlog.get caches its values, without
making a copy (if necessary) after calling readsubtree(), we might end up
adjusting the state of the same object on different contexts, breaking things
like dirty state tracking (and probably other things).

Differential Revision: https://phab.mercurial-scm.org/D4874

mercurial/manifest.py

@@ -701,14 +701,21 b' class treemanifest(object):'
         return self._dir + path
 
     def _loadalllazy(self):
-        for k, (path, node, readsubtree) in self._lazydirs.iteritems():
-            self._dirs[k] = readsubtree(path, node)
+        selfdirs = self._dirs
+        for d, (path, node, readsubtree, docopy) in self._lazydirs.iteritems():
+            if docopy:
+                selfdirs[d] = readsubtree(path, node).copy()
+            else:
+                selfdirs[d] = readsubtree(path, node)
         self._lazydirs = {}
 
     def _loadlazy(self, d):
         v = self._lazydirs.get(d)
         if v:
-            path, node, readsubtree = v
+            path, node, readsubtree, docopy = v
+            if docopy:
+                self._dirs[d] = readsubtree(path, node).copy()
+            else:
             self._dirs[d] = readsubtree(path, node)
             del self._lazydirs[d]
 
@@ -1170,7 +1177,9 b' class treemanifest(object):'
         for f, n, fl in _parse(text):
             if fl == 't':
                 f = f + '/'
-                selflazy[f] = (subpath(f), n, readsubtree)
+                # False below means "doesn't need to be copied" and can use the
+                # cached value from readsubtree directly.
+                selflazy[f] = (subpath(f), n, readsubtree, False)
             elif '/' in f:
                 # This is a flat manifest, so use __setitem__ and setflag rather
                 # than assigning directly to _files and _flags, so we can
@@ -1197,8 +1206,7 b' class treemanifest(object):'
         """
         self._load()
         flags = self.flags
-        lazydirs = [(d[:-1], node, 't') for
-                    d, (path, node, readsubtree) in self._lazydirs.iteritems()]
+        lazydirs = [(d[:-1], v[1], 't') for d, v in self._lazydirs.iteritems()]
         dirs = [(d[:-1], self._dirs[d]._node, 't') for d in self._dirs]
         files = [(f, self._files[f], flags(f)) for f in self._files]
         return _text(sorted(dirs + files + lazydirs))