revlog: introduce an explicit NodeMap class for pure code

This class make the "pure" nodemap raise the same exception than the C-extension
one.

This is a step toward unifying nodemap and index, the class is not meant to
survive on the long run.

This work is part of a refactoring to unify the revlog index and the nodemap.
This unification prepare the use of a persistent nodemap.

There is a new `isinstance` call, it will be cleaned up in coming changesets.

Differential Revision: https://phab.mercurial-scm.org/D7312

mercurial/revlog.py

@@ -65,6 +65,7 b' from . import ('
     mdiff,
     policy,
     pycompat,
+    revlogutils,
     templatefilters,
     util,
 )
@@ -217,7 +218,7 b' class revlogoldio(object):'
     def parseindex(self, data, inline):
         s = self.size
         index = []
-        nodemap = {nullid: nullrev}
+        nodemap = revlogutils.NodeMap({nullid: nullrev})
         n = off = 0
         l = len(data)
         while off + s <= l:
@@ -375,7 +376,7 b' class revlog(object):'
         # Mapping of partial identifiers to full nodes.
         self._pcache = {}
         # Mapping of revision integer to full node.
-        self._nodecache = {nullid: nullrev}
+        self._nodecache = revlogutils.NodeMap({nullid: nullrev})
         self._nodepos = None
         self._compengine = b'zlib'
         self._compengineopts = {}
@@ -652,7 +653,7 b' class revlog(object):'
             # object.
             self._nodecache.clearcaches()
         except AttributeError:
-            self._nodecache = {nullid: nullrev}
+            self._nodecache = revlogutils.NodeMap({nullid: nullrev})
             self._nodepos = None
 
     def rev(self, node):
@@ -661,11 +662,12 b' class revlog(object):'
         except TypeError:
             raise
         except error.RevlogError:
+            if not isinstance(self._nodecache, revlogutils.NodeMap):
             # parsers.c radix tree lookup failed
             if node == wdirid or node in wdirfilenodeids:
                 raise error.WdirUnsupported
             raise error.LookupError(node, self.indexfile, _(b'no node'))
-        except KeyError:
+            else:
             # pure python cache lookup failed
             n = self._nodecache
             i = self.index

mercurial/revlogutils/__init__.py

@@ -0,0 +1,14 b''
+# mercurial.revlogutils -- basic utilities for revlog
+#
+# Copyright 2019 Pierre-Yves David <[e-mail]>
+#
+# This software may be used and distributed according to the terms of the
+# GNU General Public License version 2 or any later version.
+
+from __future__ import absolute_import
+from .. import error
+
+
+class NodeMap(dict):
+    def __missing__(self, x):
+        raise error.RevlogError('unknown node: %s' % x)