rust-dirstate: call new "dirs" rust implementation from Python

This is a simple module attribute replacement, will take precedence over the
Python and C implementations.

Differential Revision: https://phab.mercurial-scm.org/D6395

mercurial/util.py

@@ -53,6 +53,8 b' from .utils import ('
     stringutil,
 )
 
+rustdirs = policy.importrust('dirstate', 'Dirs')
+
 base85 = policy.importmod(r'base85')
 osutil = policy.importmod(r'osutil')
 parsers = policy.importmod(r'parsers')
@@ -3204,6 +3206,9 b' class dirs(object):'
 if safehasattr(parsers, 'dirs'):
     dirs = parsers.dirs
 
+if rustdirs is not None:
+    dirs = rustdirs
+
 def finddirs(path):
     pos = path.rfind('/')
     while pos != -1: