resourceutil: implement `is_resource()`

This will be needed when iterating resources.

Differential Revision: https://phab.mercurial-scm.org/D7773

mercurial/utils/resourceutil.py

@@ -1,59 +1,74 b''
 # resourceutil.py - utility for looking up resources
 #
 #  Copyright 2005 K. Thananchayan <[e-mail]>
 #  Copyright 2005-2007 Matt Mackall <[e-mail]>
 #  Copyright 2006 Vadim Gelfer <[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
 
 import imp
 import os
 import sys
 
 from .. import pycompat
 
 
 def mainfrozen():
     """return True if we are a frozen executable.
 
     The code supports py2exe (most common, Windows only) and tools/freeze
     (portable, not much used).
     """
     return (
         pycompat.safehasattr(sys, "frozen")
         or pycompat.safehasattr(sys, "importers")  # new py2exe
         or imp.is_frozen("__main__")  # old py2exe
     )  # tools/freeze
 
 
 # the location of data files matching the source code
 if mainfrozen() and getattr(sys, 'frozen', None) != 'macosx_app':
     # executable version (py2exe) doesn't support __file__
     datapath = os.path.dirname(pycompat.sysexecutable)
 else:
     datapath = os.path.dirname(os.path.dirname(pycompat.fsencode(__file__)))
     _rootpath = os.path.dirname(datapath)
 
 try:
     from importlib import resources
 
+    from .. import encoding
+
     # Force loading of the resources module
     resources.open_binary  # pytype: disable=module-attr
 
     def open_resource(package, name):
         return resources.open_binary(  # pytype: disable=module-attr
             pycompat.sysstr(package), pycompat.sysstr(name)
         )
 
+    def is_resource(package, name):
+        return resources.is_resource(
+            pycompat.sysstr(package), encoding.strfromlocal(name)
+        )
+
 
 except (ImportError, AttributeError):
 
     def _package_path(package):
         return os.path.join(_rootpath, *package.split(b'.'))
 
     def open_resource(package, name):
         path = os.path.join(_package_path(package), name)
         return open(path, 'rb')
+
+    def is_resource(package, name):
+        path = os.path.join(_package_path(package), name)
+
+        try:
+            return os.path.isfile(pycompat.fsdecode(path))
+        except (IOError, OSError):
+            return False