Validation: Allow to limit maximum number of validation errors

Replicates graphql/graphql-js@4339864

Author: Cito

README.md

@@ -16,7 +16,7 @@ The current version 3.0.0a2 of GraphQL-core is up-to-date
 with GraphQL.js version 14.4.2.
 
 All parts of the API are covered by an extensive test suite
-of currently 1979 unit tests.
+of currently 1981 unit tests.
 
 
 ## Documentation

src/graphql/validation/validate.py

@@ -12,11 +12,16 @@
 __all__ = ["assert_valid_sdl", "assert_valid_sdl_extension", "validate", "validate_sdl"]
 
 
+class ValidationAbortedError(RuntimeError):
+    """Error when a validation has been aborted (error limit reached)."""
+
+
 def validate(
     schema: GraphQLSchema,
     document_ast: DocumentNode,
     rules: Sequence[RuleType] = None,
     type_info: TypeInfo = None,
+    max_errors: int = None,
 ) -> List[GraphQLError]:
     """Implements the "Validation" section of the spec.
 
@@ -45,13 +50,34 @@ def validate(
         rules = specified_rules
     elif not isinstance(rules, (list, tuple)):
         raise TypeError("Rules must be passed as a list/tuple.")
-    context = ValidationContext(schema, document_ast, type_info)
+    if max_errors is not None and not isinstance(max_errors, int):
+        raise TypeError("The maximum number of errors must be passed as an int.")
+
+    errors: List[GraphQLError] = []
+
+    def on_error(error: GraphQLError) -> None:
+        if max_errors is not None and len(errors) >= max_errors:
+            errors.append(
+                GraphQLError(
+                    "Too many validation errors, error limit reached."
+                    " Validation aborted."
+                )
+            )
+            raise ValidationAbortedError
+        errors.append(error)
+
+    context = ValidationContext(schema, document_ast, type_info, on_error)
+
     # This uses a specialized visitor which runs multiple visitors in parallel,
     # while maintaining the visitor skip and break API.
     visitors = [rule(context) for rule in rules]
+
     # Visit the whole document with each instance of all provided rules.
-    visit(document_ast, TypeInfoVisitor(type_info, ParallelVisitor(visitors)))
-    return context.errors
+    try:
+        visit(document_ast, TypeInfoVisitor(type_info, ParallelVisitor(visitors)))
+    except ValidationAbortedError:
+        pass
+    return errors
 
 
 def validate_sdl(

src/graphql/validation/validation_context.py

@@ -1,4 +1,4 @@
-from typing import Any, Dict, List, NamedTuple, Optional, Set, Union, cast
+from typing import Any, Callable, Dict, List, NamedTuple, Optional, Set, Union, cast
 
 from ..error import GraphQLError
 from ..language import (
@@ -62,10 +62,14 @@ class ASTValidationContext:
     """
 
     document: DocumentNode
+    on_error: Optional[Callable[[GraphQLError], None]]
     errors: List[GraphQLError]
 
-    def __init__(self, ast: DocumentNode) -> None:
+    def __init__(
+        self, ast: DocumentNode, on_error: Callable[[GraphQLError], None] = None
+    ) -> None:
         self.document = ast
+        self.on_error = on_error
         self.errors = []
         self._fragments: Optional[Dict[str, FragmentDefinitionNode]] = None
         self._fragment_spreads: Dict[SelectionSetNode, List[FragmentSpreadNode]] = {}
@@ -75,6 +79,8 @@ def __init__(self, ast: DocumentNode) -> None:
 
     def report_error(self, error: GraphQLError):
         self.errors.append(error)
+        if self.on_error:
+            self.on_error(error)
 
     def get_fragment(self, name: str) -> Optional[FragmentDefinitionNode]:
         fragments = self._fragments
@@ -146,8 +152,13 @@ class SDLValidationContext(ASTValidationContext):
 
     schema: Optional[GraphQLSchema]
 
-    def __init__(self, ast: DocumentNode, schema: GraphQLSchema = None) -> None:
-        super().__init__(ast)
+    def __init__(
+        self,
+        ast: DocumentNode,
+        schema: GraphQLSchema = None,
+        on_error: Callable[[GraphQLError], None] = None,
+    ) -> None:
+        super().__init__(ast, on_error)
         self.schema = schema
 
 
@@ -162,9 +173,13 @@ class ValidationContext(ASTValidationContext):
     schema: GraphQLSchema
 
     def __init__(
-        self, schema: GraphQLSchema, ast: DocumentNode, type_info: TypeInfo
+        self,
+        schema: GraphQLSchema,
+        ast: DocumentNode,
+        type_info: TypeInfo,
+        on_error: Callable[[GraphQLError], None] = None,
     ) -> None:
-        super().__init__(ast)
+        super().__init__(ast, on_error)
         self.schema = schema
         self._type_info = type_info
         self._variable_usages: Dict[NodeWithSelectionSet, List[VariableUsage]] = {}

tests/validation/test_validation.py

@@ -72,3 +72,42 @@ def validates_using_a_custom_type_info():
             "Cannot query field 'isHousetrained' on type 'Dog'."
             " Did you mean 'isHousetrained'?",
         ]
+
+
+def describe_validate_limit_maximum_number_of_validation_errors():
+    query = """
+        {
+          firstUnknownField
+          secondUnknownField
+          thirdUnknownField
+        }
+        """
+    doc = parse(query, no_location=True)
+
+    def _validate_document(max_errors=None):
+        return validate(test_schema, doc, max_errors=max_errors)
+
+    def _invalid_field_error(field_name: str):
+        return {
+            "message": f"Cannot query field '{field_name}' on type 'QueryRoot'.",
+            "locations": [],
+        }
+
+    def when_max_errors_is_equal_to_number_of_errors():
+        errors = _validate_document(max_errors=3)
+        assert errors == [
+            _invalid_field_error("firstUnknownField"),
+            _invalid_field_error("secondUnknownField"),
+            _invalid_field_error("thirdUnknownField"),
+        ]
+
+    def when_max_errors_is_less_than_number_of_errors():
+        errors = _validate_document(max_errors=2)
+        assert errors == [
+            _invalid_field_error("firstUnknownField"),
+            _invalid_field_error("secondUnknownField"),
+            {
+                "message": "Too many validation errors, error limit reached."
+                " Validation aborted."
+            },
+        ]