Move the empty fragment stripping to Resource.id

Fine, given we are anyways doing this for Registry.contents, this
feels slightly better, as otherwise someone wouldn't anyhow have a
way to create some specification where empty fragments are
meaningful but still call contents().

So, let's try this.

Author: Julian

referencing/_core.py

@@ -142,7 +142,10 @@ def id(self) -> URI | None:
         """
         Retrieve this resource's (specification-specific) identifier.
         """
-        return self._specification.id_of(self.contents)
+        id = self._specification.id_of(self.contents)
+        if id is None:
+            return
+        return id.rstrip("#")
 
     def subresources(self) -> Iterable[Resource[D]]:
         """

referencing/jsonschema.py

@@ -36,25 +36,23 @@ class UnknownDialect(Exception):
 def _dollar_id(contents: Schema) -> URI | None:
     if isinstance(contents, bool):
         return
-    id = contents.get("$id")
-    if id is not None:
-        return id.rstrip("#")
+    return contents.get("$id")
 
 
 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.rstrip("#")
+        return id
 
 
 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.rstrip("#")
+        return id
 
 
 def _anchor(

referencing/tests/test_core.py

@@ -610,6 +610,11 @@ def test_id_delegates_to_specification(self):
         )
         assert resource.id() == "urn:fixedID"
 
+    def test_id_strips_empty_fragment(self):
+        uri = "http://example.com/"
+        root = ID_AND_CHILDREN.create_resource({"ID": uri + "#"})
+        assert root.id() == uri
+
     def test_subresources_delegates_to_specification(self):
         resource = ID_AND_CHILDREN.create_resource({"children": [{}, 12]})
         assert list(resource.subresources()) == [

referencing/tests/test_jsonschema.py

@@ -65,22 +65,6 @@ 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",
     [