[validation] Add "onError" option to allow for custom error handling behavior when performing validation

src/validation/ValidationContext.js

@@ -41,6 +41,7 @@ type VariableUsage = {|
  */
 export class ASTValidationContext {
   _ast: DocumentNode;
+  _onError: ?(err: GraphQLError) => void;
   _errors: Array<GraphQLError>;
   _fragments: ?ObjMap<FragmentDefinitionNode>;
   _fragmentSpreads: Map<SelectionSetNode, $ReadOnlyArray<FragmentSpreadNode>>;
@@ -49,18 +50,23 @@ export class ASTValidationContext {
     $ReadOnlyArray<FragmentDefinitionNode>,
   >;
 
-  constructor(ast: DocumentNode): void {
+  constructor(ast: DocumentNode, onError?: (err: GraphQLError) => void): void {
     this._ast = ast;
     this._errors = [];
     this._fragments = undefined;
     this._fragmentSpreads = new Map();
     this._recursivelyReferencedFragments = new Map();
+    this._onError = onError;
   }
 
   reportError(error: GraphQLError): void {
     this._errors.push(error);
+    if (this._onError) {
+      this._onError(error);
+    }
   }
 
+  // @deprecated: use onError callback instead - will be removed in v15.
   getErrors(): $ReadOnlyArray<GraphQLError> {
     return this._errors;
   }
@@ -140,8 +146,12 @@ export type ASTValidationRule = ASTValidationContext => ASTVisitor;
 export class SDLValidationContext extends ASTValidationContext {
   _schema: ?GraphQLSchema;
 
-  constructor(ast: DocumentNode, schema?: ?GraphQLSchema): void {
-    super(ast);
+  constructor(
+    ast: DocumentNode,
+    schema: ?GraphQLSchema,
+    onError: (err: GraphQLError) => void,
+  ): void {
+    super(ast, onError);
     this._schema = schema;
   }
 
@@ -165,8 +175,9 @@ export class ValidationContext extends ASTValidationContext {
     schema: GraphQLSchema,
     ast: DocumentNode,
     typeInfo: TypeInfo,
+    onError?: (err: GraphQLError) => void,
   ): void {
-    super(ast);
+    super(ast, onError);
     this._schema = schema;
     this._typeInfo = typeInfo;
     this._variableUsages = new Map();

src/validation/__tests__/validation-test.js

@@ -75,3 +75,46 @@ describe('Validate: Supports full validation', () => {
     ]);
   });
 });
+
+describe('Validate: Limit maximum number of validation errors', () => {
+  const query = `
+    {
+      firstUnknownField
+      secondUnknownField
+      thirdUnknownField
+    }
+  `;
+  const doc = parse(query, { noLocation: true });
+
+  function validateDocument(options) {
+    return validate(testSchema, doc, undefined, undefined, options);
+  }
+
+  function invalidFieldError(fieldName) {
+    return {
+      message: `Cannot query field "${fieldName}" on type "QueryRoot".`,
+      locations: [],
+    };
+  }
+
+  it('when maxErrors is equal to number of errors', () => {
+    const errors = validateDocument({ maxErrors: 3 });
+    expect(errors).to.be.deep.equal([
+      invalidFieldError('firstUnknownField'),
+      invalidFieldError('secondUnknownField'),
+      invalidFieldError('thirdUnknownField'),
+    ]);
+  });
+
+  it('when maxErrors is less than number of errors', () => {
+    const errors = validateDocument({ maxErrors: 2 });
+    expect(errors).to.be.deep.equal([
+      invalidFieldError('firstUnknownField'),
+      invalidFieldError('secondUnknownField'),
+      {
+        message:
+          'Too many validation errors, error limit reached. Validation aborted.',
+      },
+    ]);
+  });
+});

src/validation/validate.js

@@ -2,7 +2,7 @@
 
 import devAssert from '../jsutils/devAssert';
 
-import { type GraphQLError } from '../error/GraphQLError';
+import { GraphQLError } from '../error/GraphQLError';
 
 import { type DocumentNode } from '../language/ast';
 import { visit, visitInParallel, visitWithTypeInfo } from '../language/visitor';
@@ -20,6 +20,8 @@ import {
   ValidationContext,
 } from './ValidationContext';
 
+export const ABORT_VALIDATION = Object.freeze({});
+
 /**
  * Implements the "Validation" section of the spec.
  *
@@ -41,18 +43,45 @@ export function validate(
   documentAST: DocumentNode,
   rules?: $ReadOnlyArray<ValidationRule> = specifiedRules,
   typeInfo?: TypeInfo = new TypeInfo(schema),
+  options?: {| maxErrors?: number |},
 ): $ReadOnlyArray<GraphQLError> {
   devAssert(documentAST, 'Must provide document');
   // If the schema used for validation is invalid, throw an error.
   assertValidSchema(schema);
 
-  const context = new ValidationContext(schema, documentAST, typeInfo);
+  const abortObj = Object.freeze({});
+  const errors = [];
+  const maxErrors = options && options.maxErrors;
+  const context = new ValidationContext(
+    schema,
+    documentAST,
+    typeInfo,
+    error => {
+      if (maxErrors != null && errors.length >= maxErrors) {
+        errors.push(
+          new GraphQLError(
+            'Too many validation errors, error limit reached. Validation aborted.',
+          ),
+        );
+        throw abortObj;
+      }
+      errors.push(error);
+    },
+  );
+
   // This uses a specialized visitor which runs multiple visitors in parallel,
   // while maintaining the visitor skip and break API.
   const visitor = visitInParallel(rules.map(rule => rule(context)));
+
   // Visit the whole document with each instance of all provided rules.
-  visit(documentAST, visitWithTypeInfo(typeInfo, visitor));
-  return context.getErrors();
+  try {
+    visit(documentAST, visitWithTypeInfo(typeInfo, visitor));
+  } catch (e) {
+    if (e !== abortObj) {
+      throw e;
+    }
+  }
+  return errors;
 }
 
 // @internal
@@ -61,10 +90,18 @@ export function validateSDL(
   schemaToExtend?: ?GraphQLSchema,
   rules?: $ReadOnlyArray<SDLValidationRule> = specifiedSDLRules,
 ): $ReadOnlyArray<GraphQLError> {
-  const context = new SDLValidationContext(documentAST, schemaToExtend);
+  const errors = [];
+  const context = new SDLValidationContext(
+    documentAST,
+    schemaToExtend,
+    error => {
+      errors.push(error);
+    },
+  );
+
   const visitors = rules.map(rule => rule(context));
   visit(documentAST, visitInParallel(visitors));
-  return context.getErrors();
+  return errors;
 }
 
 /**