revlog: use "entry_point" phrasing for loading the revlog

The main entry for the revlog will not necessary be the index, but a small
"docket". So we change the variable names and we move the initialisation of the
index_file and data_file after that first entry point have been read.

Differential Revision: https://phab.mercurial-scm.org/D10601

mercurial/revlog.py

@@ -469,21 +469,13 b' class revlog(object):'
         new_header, mmapindexthreshold, force_nodemap = self._init_opts()
 
         if self.postfix is None:
-            index_file = b'%s.i' % self.radix
-            data_file = b'%s.d' % self.radix
-        elif self.postfix == b'a':
-            index_file = b'%s.i.a' % self.radix
-            data_file = b'%s.d' % self.radix
+            entry_point = b'%s.i' % self.radix
         else:
-            index_file = b'%s.i.%s' % (self.radix, self.postfix)
-            data_file = b'%s.d.%s' % (self.radix, self.postfix)
-
-        self._indexfile = index_file
-        self._datafile = data_file
+            entry_point = b'%s.i.%s' % (self.radix, self.postfix)
 
         indexdata = b''
         self._initempty = True
-        indexdata = self._get_data(self._indexfile, mmapindexthreshold)
+        indexdata = self._get_data(entry_point, mmapindexthreshold)
         if len(indexdata) > 0:
             header = INDEX_HEADER.unpack(indexdata[:4])[0]
             self._initempty = False
@@ -533,6 +525,13 b' class revlog(object):'
             msg %= (self._format_version, self.display_id)
             raise error.RevlogError(msg)
 
+        self._indexfile = entry_point
+
+        if self.postfix is None or self.postfix == b'a':
+            self._datafile = b'%s.d' % self.radix
+        else:
+            self._datafile = b'%s.d.%s' % (self.radix, self.postfix)
+
         self.nodeconstants = sha1nodeconstants
         self.nullid = self.nodeconstants.nullid