nodemap: provide the on disk data to indexes who support it

Time to start defining the API and prepare the rust index support. We provide
a method to do so. We use a distinct method instead of passing them in the
constructor because we will need this method anyway later (to refresh the mmap
once we update the data on disk).

Differential Revision: https://phab.mercurial-scm.org/D7847

mercurial/pure/parsers.py

@@ -156,6 +156,14 b' class PersistentNodeMapIndexObject(Index'
         index."""
         return nodemaputil.persistent_data(self)
 
+    def update_nodemap_data(self, nm_data):
+        """provide full blokc of persisted binary data for a nodemap
+
+        The data are expected to come from disk. See `nodemap_data_all` for a
+        produceur of such data."""
+        if nm_data is not None:
+            nodemaputil.parse_data(nm_data)
+
 
 class InlinedIndexObject(BaseIndexObject):
     def __init__(self, data, inline=0):

mercurial/revlog.py

@@ -626,6 +626,16 b' class revlog(object):'
             self._io = rustrevlogio()
         try:
             d = self._io.parseindex(indexdata, self._inline)
+            index, _chunkcache = d
+            use_nodemap = (
+                not self._inline
+                and self.nodemap_file is not None
+                and util.safehasattr(index, 'update_nodemap_data')
+            )
+            if use_nodemap:
+                nodemap_data = nodemaputil.persisted_data(self)
+                if nodemap_data is not None:
+                    index.update_nodemap_data(nodemap_data)
         except (ValueError, IndexError):
             raise error.RevlogError(
                 _(b"index %s is corrupted") % self.indexfile