Gut the meat of the recursiveRef implementation for draft2019

It's buggy, and can lead to blowing up the stack with recursion errors.

Done by (redundantly) checking schemas during test runs, even though the
upstream test suite 'guarantees' they're valid. (Given that it uses this
implementation to make that guarantee, bugs like the above went unnoticed.)

Closes: #847

jsonschema/_legacy_validators.py

@@ -221,4 +221,8 @@ def recursiveRef(validator, recursiveRef, instance, schema):
 
     fragment = recursiveRef.lstrip("#")
     subschema = validator.resolver.resolve_fragment(target, fragment)
-    yield from validator.descend(instance, subschema)
+    # FIXME: This is gutted (and not calling .descend) because it can trigger
+    #        recursion errors, so there's a bug here. Re-enable the tests to
+    #        see it.
+    subschema
+    return []

jsonschema/tests/_suite.py

@@ -197,6 +197,7 @@ def fn(this):
         return unittest.skipIf(reason is not None, reason)(fn)
 
     def validate(self, Validator, **kwargs):
+        Validator.check_schema(self.schema)
         resolver = jsonschema.RefResolver.from_schema(
             schema=self.schema,
             store=self._remotes,

jsonschema/tests/test_jsonschema_test_suite.py

@@ -360,6 +360,18 @@ def leap_second(test):
             message="dynamicRef support isn't working yet.",
             subject="recursiveRef",
         )(test)
+        or skip(
+            message="These tests depends on dynamicRef working.",
+            subject="id",
+            case_description=(
+                "Invalid use of fragments in location-independent $id"
+            ),
+        )(test)
+        or skip(
+            message="These tests depends on dynamicRef working.",
+            subject="defs",
+            description="invalid definition schema",
+        )(test)
         or skip(
             message="These tests depends on dynamicRef working.",
             subject="anchor",

jsonschema/tests/test_validators.py

@@ -1410,7 +1410,7 @@ class MetaSchemaTestsMixin(object):
     # TODO: These all belong upstream
     def test_invalid_properties(self):
         with self.assertRaises(exceptions.SchemaError):
-            self.Validator.check_schema({"properties": {"test": object()}})
+            self.Validator.check_schema({"properties": 12})
 
     def test_minItems_invalid_string(self):
         with self.assertRaises(exceptions.SchemaError):