Add --validator-class option for passing a validator class

docs/usage.rst

@@ -251,3 +251,26 @@ not set.
 
 ``--base-uri`` overrides this behavior, setting a custom base URI for ``$ref``
 resolution.
+
+``--validator-class``
+~~~~~~~~~~~~~~~~~~~~~
+
+``check-jsonschema`` allows users to pass a custom validator class which
+implements the ``jsonschema.protocols.Validator`` protocol.
+
+The format used for this argument is ``<module>:<class>``. For example, to
+explicitly use the ``jsonschema`` validator for Draft7, use
+``--validator-class 'jsonschema.validators:Draft7Validator'``.
+
+The module containing the validator class must be importable from within the
+``check-jsonschema`` runtime context.
+
+.. note::
+
+    ``check-jsonschema`` will treat the validator class similarly to the
+    ``jsonschema`` library builtin validators. This includes using documented
+    extension points like passing a format checker or the behavior enabled with
+    ``--fill-defaults``. Users of this feature are recommended to build their
+    validators using ``jsonschema``'s documented interfaces (e.g.
+    ``jsonschema.validators.extend``) to ensure that their validators are
+    compatible.

src/check_jsonschema/cli/main_command.py

@@ -4,6 +4,7 @@
 import textwrap
 
 import click
+import jsonschema
 
 from ..catalog import CUSTOM_SCHEMA_NAMES, SCHEMA_CATALOG
 from ..checker import SchemaChecker
@@ -18,7 +19,7 @@
     SchemaLoaderBase,
 )
 from ..transforms import TRANSFORM_LIBRARY
-from .param_types import CommaDelimitedList
+from .param_types import CommaDelimitedList, ValidatorClassName
 from .parse_result import ParseResult, SchemaLoadingMode
 
 BUILTIN_SCHEMA_NAMES = [f"vendor.{k}" for k in SCHEMA_CATALOG.keys()] + [
@@ -169,13 +170,27 @@ def pretty_helptext_list(values: list[str] | tuple[str, ...]) -> str:
 )
 @click.option(
     "--fill-defaults",
-    help="Autofill 'default' values prior to validation.",
+    help=(
+        "Autofill 'default' values prior to validation. "
+        "This may conflict with certain third-party validators used with "
+        "'--validator-class'"
+    ),
     is_flag=True,
 )
+@click.option(
+    "--validator-class",
+    help=(
+        "The fully qualified name of a python validator to use in place of "
+        "the 'jsonschema' library validators, in the form of '<package>:<class>'. "
+        "The validator must be importable in the same environment where "
+        "'check-jsonschema' is run."
+    ),
+    type=ValidatorClassName(),
+)
 @click.option(
     "-o",
     "--output-format",
-    help="Which output format to use",
+    help="Which output format to use.",
     type=click.Choice(tuple(REPORTER_BY_NAME.keys()), case_sensitive=False),
     default="text",
 )
@@ -217,6 +232,7 @@ def main(
     traceback_mode: str,
     data_transform: str | None,
     fill_defaults: bool,
+    validator_class: type[jsonschema.protocols.Validator] | None,
     output_format: str,
     verbose: int,
     quiet: int,
@@ -225,6 +241,8 @@ def main(
     args = ParseResult()
 
     args.set_schema(schemafile, builtin_schema, check_metaschema)
+    args.set_validator(validator_class)
+
     args.base_uri = base_uri
     args.instancefiles = instancefiles
 
@@ -272,6 +290,7 @@ def build_schema_loader(args: ParseResult) -> SchemaLoaderBase:
             args.cache_filename,
             args.disable_cache,
             base_uri=args.base_uri,
+            validator_class=args.validator_class,
         )
     else:
         raise NotImplementedError("no valid schema option provided")

src/check_jsonschema/cli/param_types.py

@@ -1,11 +1,16 @@
 from __future__ import annotations
 
+import importlib
+import re
 import typing as t
 
 import click
+import jsonschema
 
 
 class CommaDelimitedList(click.ParamType):
+    name = "comma_delimited"
+
     def __init__(
         self,
         *,
@@ -43,3 +48,59 @@ def convert(
                 )
 
         return resolved
+
+
+class ValidatorClassName(click.ParamType):
+    name = "validator"
+
+    def convert(
+        self, value: str, param: click.Parameter | None, ctx: click.Context | None
+    ) -> type[jsonschema.protocols.Validator]:
+        """
+        Use a colon-based parse to split this up and do the import with importlib.
+        This method is inspired by pkgutil.resolve_name and uses the newer syntax
+        documented there.
+
+        pkgutil supports both
+            W(.W)*
+        and
+            W(.W)*:(W(.W)*)?
+        as patterns, but notes that the first one is for backwards compatibility only.
+        The second form is preferred because it clarifies the division between the
+        importable name and any namespaced path to an object or class.
+
+        As a result, only one import is needed, rather than iterative imports over the
+        list of names.
+        """
+        value = super().convert(value, param, ctx)
+        pattern = re.compile(
+            r"^(?P<pkg>(?!\d)(\w+)(\.(?!\d)(\w+))*):"
+            r"(?P<cls>(?!\d)(\w+)(\.(?!\d)(\w+))*)$"
+        )
+        m = pattern.match(value)
+        if m is None:
+            self.fail(
+                f"'{value}' is not a valid specifier in '<package>:<class>' form",
+                param,
+                ctx,
+            )
+        pkg = m.group("pkg")
+        classname = m.group("cls")
+        try:
+            result: t.Any = importlib.import_module(pkg)
+        except ImportError as e:
+            self.fail(f"'{pkg}' was not an importable module. {str(e)}", param, ctx)
+        try:
+            for part in classname.split("."):
+                result = getattr(result, part)
+        except AttributeError as e:
+            self.fail(
+                f"'{classname}' was not resolvable to a class in '{pkg}'. {str(e)}",
+                param,
+                ctx,
+            )
+
+        if not isinstance(result, type):
+            self.fail(f"'{classname}' in '{pkg}' is not a class", param, ctx)
+
+        return t.cast(t.Type[jsonschema.protocols.Validator], result)

src/check_jsonschema/cli/parse_result.py

@@ -3,6 +3,7 @@
 import enum
 
 import click
+import jsonschema
 
 from ..formats import FormatOptions, RegexVariantName
 from ..transforms import Transform
@@ -28,7 +29,8 @@ def __init__(self) -> None:
         self.default_filetype: str = "json"
         # data-transform (for Azure Pipelines and potentially future transforms)
         self.data_transform: Transform | None = None
-        # fill default values on instances during validation
+        # validation behavioral controls
+        self.validator_class: type[jsonschema.protocols.Validator] | None = None
         self.fill_defaults: bool = False
         # regex format options
         self.disable_all_formats: bool = False
@@ -65,6 +67,17 @@ def set_schema(
         else:
             self.schema_mode = SchemaLoadingMode.metaschema
 
+    def set_validator(
+        self, validator_class: type[jsonschema.protocols.Validator] | None
+    ) -> None:
+        if validator_class is None:
+            return
+        if self.schema_mode != SchemaLoadingMode.filepath:
+            raise click.UsageError(
+                "--validator-class can only be used with --schemafile for schema loading"
+            )
+        self.validator_class = validator_class
+
     @property
     def format_opts(self) -> FormatOptions:
         return FormatOptions(

src/check_jsonschema/schema_loader/main.py

@@ -56,18 +56,22 @@ def get_validator(
 
 
 class SchemaLoader(SchemaLoaderBase):
+    validator_class: type[jsonschema.protocols.Validator] | None = None
+
     def __init__(
         self,
         schemafile: str,
         cache_filename: str | None = None,
         disable_cache: bool = False,
         base_uri: str | None = None,
+        validator_class: type[jsonschema.protocols.Validator] | None = None,
     ) -> None:
         # record input parameters (these are not to be modified)
         self.schemafile = schemafile
         self.cache_filename = cache_filename
         self.disable_cache = disable_cache
         self.base_uri = base_uri
+        self.validator_class = validator_class
 
         # if the schema location is a URL, which may include a file:// URL, parse it
         self.url_info = None
@@ -132,9 +136,19 @@ def get_validator(
             self._parsers, retrieval_uri, schema
         )
 
-        # get the correct validator class and check the schema under its metaschema
-        validator_cls = jsonschema.validators.validator_for(schema)
-        validator_cls.check_schema(schema)
+        if self.validator_class is None:
+            # get the correct validator class and check the schema under its metaschema
+            validator_cls = jsonschema.validators.validator_for(schema)
+            validator_cls.check_schema(schema)
+        else:
+            # for a user-provided validator class, don't check_schema
+            # on the grounds that it might *not* be valid but the user wants to use
+            # their custom validator anyway
+            #
+            # in fact, there's no real guarantee that a user-provided
+            # validator_class properly conforms to the jsonschema.Validator protocol
+            # we *hope* that it does, but we can't be fully sure
+            validator_cls = self.validator_class
 
         # extend the validator class with default-filling behavior if appropriate
         if fill_defaults: