Implement the get_resource_reader() API for file system imports (#5168)

Lib/importlib/_bootstrap_external.py

@@ -6,12 +6,11 @@ such it requires the injection of specific modules and attributes in order to
 work. One should use importlib as the public-facing version of this module.
 
 """
-#
-# IMPORTANT: Whenever making changes to this module, be sure to run
-# a top-level make in order to get the frozen version of the module
-# updated. Not doing so will result in the Makefile to fail for
-# all others who don't have a ./python around to freeze the module
-# in the early stages of compilation.
+# IMPORTANT: Whenever making changes to this module, be sure to run a top-level
+# `make regen-importlib` followed by `make` in order to get the frozen version
+# of the module updated. Not doing so will result in the Makefile to fail for
+# all others who don't have a ./python around to freeze the module in the early
+# stages of compilation.
 #
 
 # See importlib._setup() for what is injected into the global namespace.
@@ -911,6 +910,33 @@ class FileLoader:
         with _io.FileIO(path, 'r') as file:
             return file.read()
 
+    # ResourceReader ABC API.
+
+    @_check_name
+    def get_resource_reader(self, module):
+        if self.is_package(module):
+            return self
+        return None
+
+    def open_resource(self, resource):
+        path = _path_join(_path_split(self.path)[0], resource)
+        return _io.FileIO(path, 'r')
+
+    def resource_path(self, resource):
+        if not self.is_resource(resource):
+            raise FileNotFoundError
+        path = _path_join(_path_split(self.path)[0], resource)
+        return path
+
+    def is_resource(self, name):
+        if path_sep in name:
+            return False
+        path = _path_join(_path_split(self.path)[0], name)
+        return _path_isfile(path)
+
+    def contents(self):
+        return iter(_os.listdir(_path_split(self.path)[0]))
+
 
 class SourceFileLoader(FileLoader, SourceLoader):
 

Lib/importlib/abc.py

@@ -342,7 +342,7 @@ class SourceLoader(_bootstrap_external.SourceLoader, ResourceLoader, ExecutionLo
 _register(SourceLoader, machinery.SourceFileLoader)
 
 
-class ResourceReader:
+class ResourceReader(metaclass=abc.ABCMeta):
 
     """Abstract base class to provide resource-reading support.
 
@@ -383,3 +383,6 @@ class ResourceReader:
     def contents(self):
         """Return an iterator of strings over the contents of the package."""
         return iter([])
+
+
+_register(ResourceReader, machinery.SourceFileLoader)

Lib/importlib/resources.py

@@ -59,8 +59,10 @@ def _get_resource_reader(
     # hook wants to create a weak reference to the object, but
     # zipimport.zipimporter does not support weak references, resulting in a
     # TypeError.  That seems terrible.
-    if hasattr(package.__spec__.loader, 'open_resource'):
-        return cast(resources_abc.ResourceReader, package.__spec__.loader)
+    spec = package.__spec__
+    if hasattr(spec.loader, 'get_resource_reader'):
+        return cast(resources_abc.ResourceReader,
+                    spec.loader.get_resource_reader(spec.name))
     return None
 
 

Lib/test/test_importlib/test_resource.py

@@ -1,10 +1,10 @@
 import sys
 import unittest
 
-from importlib import resources
 from . import data01
 from . import zipdata02
 from . import util
+from importlib import resources
 
 
 class ResourceTests:

Lib/test/test_importlib/util.py

@@ -397,6 +397,9 @@ class CASEOKTestBase:
 
 def create_package(file, path, is_package=True, contents=()):
     class Reader(ResourceReader):
+        def get_resource_reader(self, package):
+            return self
+
         def open_resource(self, path):
             self._path = path
             if isinstance(file, Exception):