Strip empty fragments when directly looking up a resource.

This isn't necessarily 100% 'nice feeling', but early versions
of JSON Schema used URIs with empty fragments as their $ids, and
even though later versions don't, and future versions may even
make this an error, a downstream library (including jsonschema)
is likely to copy these $ids exactly as-is and expect the resource
to be retrievable, despite the last commit making some of this
behavior JSON Schema-specific. We may revisit this all later if/when
it turns out to matter.

Refs: python-jsonschema/jsonschema#1064

Author: Julian

referencing/_core.py

@@ -362,7 +362,9 @@ def contents(self, uri: URI) -> D:
         """
         Retrieve the contents identified by the given URI.
         """
-        return self._resources[uri].contents
+        # Empty fragment URIs are equivalent to URIs without the fragment.
+        # TODO: Is this true for non JSON Schema resources? Probably not.
+        return self._resources[uri.rstrip("#")].contents
 
     def crawl(self) -> Registry[D]:
         """

referencing/tests/test_core.py

@@ -155,6 +155,12 @@ def test_contents(self):
         registry = Registry().with_resource(uri, resource)
         assert registry.contents(uri) == {"foo": "bar"}
 
+    def test_contents_strips_empty_fragments(self):
+        uri = "http://example.com/"
+        resource = ID_AND_CHILDREN.create_resource({"ID": uri + "#"})
+        registry = resource @ Registry()
+        assert registry.contents(uri) == {"ID": uri + "#"}
+
     def test_crawled_anchor(self):
         resource = ID_AND_CHILDREN.create_resource({"anchors": {"foo": "bar"}})
         registry = Registry().with_resource("urn:example", resource)