SchemaError in 4.0.1 for schema working with 3.2

[rikardn]

The schema in the example below can be used to validate the instance without problems in jsonschema 3.2, but when using 4.0.1 it gives a schema error.

import jsonschema
instance = ['A', 'B']
schema = {
  "type": "array",
  "items": [{"type": "string"}, {"type": "string"}]
}
jsonschema.validate(instance, schema)

Output:

  File "<stdin>", line 1, in <module>
  File "/home/debug/myvenv/lib/python3.8/site-packages/jsonschema/validators.py", line 963, in validate
    cls.check_schema(schema)
  File "/home/debug/myvenv/lib/python3.8/site-packages/jsonschema/validators.py", line 183, in check_schema
    raise exceptions.SchemaError.create_from(error)
jsonschema.exceptions.SchemaError: [{'type': 'string'}, {'type': 'string'}] is not of type 'object', 'boolean'

Failed validating 'type' in metaschema['allOf'][1]['properties']['items']['$dynamicRef']['allOf'][0]:
    {'$defs': {'anchorString': {'pattern': '^[A-Za-z_][-A-Za-z0-9._]*$',
                                'type': 'string'},
               'uriReferenceString': {'format': 'uri-reference',
                                      'type': 'string'},
               'uriString': {'format': 'uri', 'type': 'string'}},
     '$dynamicAnchor': 'meta',
     '$id': 'https://json-schema.org/draft/2020-12/meta/core',
     '$schema': 'https://json-schema.org/draft/2020-12/schema',
     '$vocabulary': {'https://json-schema.org/draft/2020-12/vocab/core': True},
     'properties': {'$anchor': {'$ref': '#/$defs/anchorString'},
                    '$comment': {'type': 'string'},
                    '$defs': {'additionalProperties': {'$dynamicRef': '#meta'},
                              'type': 'object'},
                    '$dynamicAnchor': {'$ref': '#/$defs/anchorString'},
                    '$dynamicRef': {'$ref': '#/$defs/uriReferenceString'},
                    '$id': {'$comment': 'Non-empty fragments not allowed.',
                            '$ref': '#/$defs/uriReferenceString',
                            'pattern': '^[^#]*#?$'},
                    '$ref': {'$ref': '#/$defs/uriReferenceString'},
                    '$schema': {'$ref': '#/$defs/uriString'},
                    '$vocabulary': {'additionalProperties': {'type': 'boolean'},
                                    'propertyNames': {'$ref': '#/$defs/uriString'},
                                    'type': 'object'}},
     'title': 'Core vocabulary meta-schema',
     'type': ['object', 'boolean']}

On schema['items']:
    [{'type': 'string'}, {'type': 'string'}]

[Julian]

Hi. Your schema doesn't use $schema to declare what version of the spec it's written for, so you're comparing behavior across different versions of the spec.

Indeed in draft 7 what you have is fine, but in newer drafts it isn't, as doing what you have there now uses prefixItems rather than items.

You should be setting $schema or at least if not, directly using a validator for the version you intend to use. And if that's draft2020-12, prefixItems.

[rikardn]

Thanks for the explanation @Julian !