Normalize JSON Schema IDs to strip empty fragments.

This is discouraged by the spec, albeit still allowed.

Future versions may fully make it an error, which is why
it seems to make sense to make this JSON Schema-specific
(rather than e.g. doing it as part of Resource.id) as some
other spec may allow it and have different behavior to my
current understanding.

Refs: python-jsonschema/jsonschema#1064

Author: Julian

referencing/jsonschema.py

@@ -36,23 +36,25 @@ class UnknownDialect(Exception):
 def _dollar_id(contents: Schema) -> URI | None:
     if isinstance(contents, bool):
         return
-    return contents.get("$id")
+    id = contents.get("$id")
+    if id is not None:
+        return id.rstrip("#")
 
 
 def _legacy_dollar_id(contents: Schema) -> URI | None:
     if isinstance(contents, bool) or "$ref" in contents:
         return
     id = contents.get("$id")
     if id is not None and not id.startswith("#"):
-        return id
+        return id.rstrip("#")
 
 
 def _legacy_id(contents: ObjectSchema) -> URI | None:
     if "$ref" in contents:
         return
     id = contents.get("id")
     if id is not None and not id.startswith("#"):
-        return id
+        return id.rstrip("#")
 
 
 def _anchor(
@@ -547,10 +549,10 @@ def maybe_in_subresource(
         for dialect_id, specification in [
             ("https://json-schema.org/draft/2020-12/schema", DRAFT202012),
             ("https://json-schema.org/draft/2019-09/schema", DRAFT201909),
-            ("http://json-schema.org/draft-07/schema#", DRAFT7),
-            ("http://json-schema.org/draft-06/schema#", DRAFT6),
-            ("http://json-schema.org/draft-04/schema#", DRAFT4),
-            ("http://json-schema.org/draft-03/schema#", DRAFT3),
+            ("http://json-schema.org/draft-07/schema", DRAFT7),
+            ("http://json-schema.org/draft-06/schema", DRAFT6),
+            ("http://json-schema.org/draft-04/schema", DRAFT4),
+            ("http://json-schema.org/draft-03/schema", DRAFT3),
         ]
     },
 )
@@ -569,7 +571,7 @@ def specification_with(
 
             if the given ``dialect_id`` isn't known
     """
-    resource = _SPECIFICATIONS.get(dialect_id)
+    resource = _SPECIFICATIONS.get(dialect_id.rstrip("#"))
     if resource is not None:
         return resource.contents
     if default is None:  # type: ignore[reportUnnecessaryComparison]

referencing/tests/test_jsonschema.py

@@ -65,6 +65,22 @@ def test_id_of_mapping(id, specification):
     assert specification.id_of({id: uri}) == uri
 
 
+@pytest.mark.parametrize(
+    "id, specification",
+    [
+        ("$id", referencing.jsonschema.DRAFT202012),
+        ("$id", referencing.jsonschema.DRAFT201909),
+        ("$id", referencing.jsonschema.DRAFT7),
+        ("$id", referencing.jsonschema.DRAFT6),
+        ("id", referencing.jsonschema.DRAFT4),
+        ("id", referencing.jsonschema.DRAFT3),
+    ],
+)
+def test_id_of_empty_fragment(id, specification):
+    uri = "http://example.com/some-schema"
+    assert specification.id_of({id: uri + "#"}) == uri
+
+
 @pytest.mark.parametrize(
     "specification",
     [
@@ -140,6 +156,31 @@ def test_specification_with(uri, expected):
     assert referencing.jsonschema.specification_with(uri) == expected
 
 
+@pytest.mark.parametrize(
+    "uri, expected",
+    [
+        (
+            "http://json-schema.org/draft-07/schema",
+            referencing.jsonschema.DRAFT7,
+        ),
+        (
+            "http://json-schema.org/draft-06/schema",
+            referencing.jsonschema.DRAFT6,
+        ),
+        (
+            "http://json-schema.org/draft-04/schema",
+            referencing.jsonschema.DRAFT4,
+        ),
+        (
+            "http://json-schema.org/draft-03/schema",
+            referencing.jsonschema.DRAFT3,
+        ),
+    ],
+)
+def test_specification_with_no_empty_fragment(uri, expected):
+    assert referencing.jsonschema.specification_with(uri) == expected
+
+
 def test_specification_with_unknown_dialect():
     dialect_id = "http://example.com/unknown-json-schema-dialect-id"
     with pytest.raises(referencing.jsonschema.UnknownDialect) as excinfo: