Add DeprecationWarning for ResourceLoader

Co-authored-by: rashansmith <[email protected]>

Author: tomasr8

Lib/importlib/abc.py

@@ -70,6 +70,15 @@ class ResourceLoader(Loader):
 
     """
 
+    def __init__(self):
+        import warnings
+        warnings.warn("importlib.abc.ResourceLoader is deprecated in "
+                      "favour of supporting resource loading through "
+                      "importlib.resources.abc.ResourceReader.",
+                      DeprecationWarning, stacklevel=2)
+        super().__init__()
+
+
     @abc.abstractmethod
     def get_data(self, path):
         """Abstract method which when implemented should return the bytes for

Lib/test/test_importlib/test_abc.py

@@ -933,5 +933,13 @@ def path_stats(self, path):
             loader.path_mtime('foo.py')
 
 
+class ResourceLoaderDeprecationWarningsTests(unittest.TestCase):
+    """Tests ResourceLoader deprecation warnings."""
+
+    def test_deprecated_resource_loader(self):
+        with self.assertWarns(DeprecationWarning):
+            from importlib.abc import ResourceLoader
+
+
 if __name__ == '__main__':
     unittest.main()