GraphQLScalarType: make 'serialize' optional with 'identityFunc' as default

src/type/__tests__/definition-test.js

@@ -25,7 +25,7 @@ import {
   GraphQLNonNull,
 } from '../definition';
 
-const ScalarType = new GraphQLScalarType({ name: 'Scalar', serialize() {} });
+const ScalarType = new GraphQLScalarType({ name: 'Scalar' });
 const ObjectType = new GraphQLObjectType({ name: 'Object', fields: {} });
 const InterfaceType = new GraphQLInterfaceType({
   name: 'Interface',
@@ -45,46 +45,28 @@ const NonNullListofScalars = GraphQLNonNull(ListOfScalarsType);
 
 describe('Type System: Scalars', () => {
   it('accepts a Scalar type defining serialize', () => {
-    expect(
-      () =>
-        new GraphQLScalarType({
-          name: 'SomeScalar',
-          serialize: () => null,
-        }),
-    ).not.to.throw();
+    expect(() => new GraphQLScalarType({ name: 'SomeScalar' })).not.to.throw();
   });
 
   it('accepts a Scalar type defining parseValue and parseLiteral', () => {
     expect(
       () =>
         new GraphQLScalarType({
           name: 'SomeScalar',
-          serialize: () => null,
           parseValue: () => null,
           parseLiteral: () => null,
         }),
     ).not.to.throw();
   });
 
   it('provides default methods if omitted', () => {
-    const scalar = new GraphQLScalarType({
-      name: 'Foo',
-      serialize: () => null,
-    });
+    const scalar = new GraphQLScalarType({ name: 'Foo' });
 
+    expect(scalar.serialize).to.equal(identityFunc);
     expect(scalar.parseValue).to.equal(identityFunc);
     expect(scalar.parseLiteral).to.equal(valueFromASTUntyped);
   });
 
-  it('rejects a Scalar type not defining serialize', () => {
-    expect(
-      // $DisableFlowOnNegativeTest
-      () => new GraphQLScalarType({ name: 'SomeScalar' }),
-    ).to.throw(
-      'SomeScalar must provide "serialize" function. If this custom Scalar is also used as an input type, ensure "parseValue" and "parseLiteral" functions are also provided.',
-    );
-  });
-
   it('rejects a Scalar type defining serialize with an incorrect type', () => {
     expect(
       () =>
@@ -103,7 +85,6 @@ describe('Type System: Scalars', () => {
       () =>
         new GraphQLScalarType({
           name: 'SomeScalar',
-          serialize: () => null,
           parseValue: () => null,
         }),
     ).to.throw(
@@ -116,7 +97,6 @@ describe('Type System: Scalars', () => {
       () =>
         new GraphQLScalarType({
           name: 'SomeScalar',
-          serialize: () => null,
           parseLiteral: () => null,
         }),
     ).to.throw(
@@ -129,7 +109,6 @@ describe('Type System: Scalars', () => {
       () =>
         new GraphQLScalarType({
           name: 'SomeScalar',
-          serialize: () => null,
           // $DisableFlowOnNegativeTest
           parseValue: {},
           // $DisableFlowOnNegativeTest

src/type/__tests__/predicate-test.js

@@ -83,10 +83,7 @@ const InputObjectType = new GraphQLInputObjectType({
   name: 'InputObject',
   fields: {},
 });
-const ScalarType = new GraphQLScalarType({
-  name: 'Scalar',
-  serialize() {},
-});
+const ScalarType = new GraphQLScalarType({ name: 'Scalar' });
 const Directive = new GraphQLDirective({
   name: 'Directive',
   locations: ['QUERY'],
@@ -711,7 +708,6 @@ describe('Directive predicates', () => {
     it('returns false for scalar type named like specified directive', () => {
       const ScalarNamedLikeDirective = new GraphQLScalarType({
         name: 'deprecated',
-        serialize: () => null,
       });
       expect(isSpecifiedDirective(ScalarNamedLikeDirective)).to.equal(false);
     });

src/type/__tests__/schema-test.js

@@ -298,10 +298,7 @@ describe('Type System: Schema', () => {
 
     describe('A Schema must contain uniquely named types', () => {
       it('rejects a Schema which redefines a built-in type', () => {
-        const FakeString = new GraphQLScalarType({
-          name: 'String',
-          serialize: () => null,
-        });
+        const FakeString = new GraphQLScalarType({ name: 'String' });
 
         const QueryType = new GraphQLObjectType({
           name: 'Query',

src/type/__tests__/validation-test.js

@@ -30,10 +30,7 @@ import { validateSchema } from '../validate';
 import { buildSchema } from '../../utilities/buildASTSchema';
 import { extendSchema } from '../../utilities/extendSchema';
 
-const SomeScalarType = new GraphQLScalarType({
-  name: 'SomeScalar',
-  serialize() {},
-});
+const SomeScalarType = new GraphQLScalarType({ name: 'SomeScalar' });
 
 const SomeInterfaceType = new GraphQLInterfaceType({
   name: 'SomeInterface',

src/type/definition.js

@@ -559,14 +559,14 @@ export class GraphQLScalarType {
   constructor(config: GraphQLScalarTypeConfig<*, *>): void {
     this.name = config.name;
     this.description = config.description;
-    this.serialize = config.serialize;
+    this.serialize = config.serialize || identityFunc;
     this.parseValue = config.parseValue || identityFunc;
     this.parseLiteral = config.parseLiteral || valueFromASTUntyped;
     this.astNode = config.astNode;
     this.extensionASTNodes = undefineIfEmpty(config.extensionASTNodes);
     invariant(typeof config.name === 'string', 'Must provide name.');
     invariant(
-      typeof config.serialize === 'function',
+      config.serialize == null || typeof config.serialize === 'function',
       `${this.name} must provide "serialize" function. If this custom Scalar ` +
         'is also used as an input type, ensure "parseValue" and "parseLiteral" functions are also provided.',
     );
@@ -582,6 +582,7 @@ export class GraphQLScalarType {
 
   toConfig(): {|
     ...GraphQLScalarTypeConfig<*, *>,
+    serialize: GraphQLScalarSerializer<*>,
     parseValue: GraphQLScalarValueParser<*>,
     parseLiteral: GraphQLScalarLiteralParser<*>,
     extensionASTNodes: $ReadOnlyArray<ScalarTypeExtensionNode>,
@@ -617,7 +618,7 @@ export type GraphQLScalarTypeConfig<TInternal, TExternal> = {|
   name: string,
   description?: ?string,
   // Serializes an internal value to include in a response.
-  serialize: GraphQLScalarSerializer<TExternal>,
+  serialize?: GraphQLScalarSerializer<TExternal>,
   // Parses an externally provided value to use as an input.
   parseValue?: GraphQLScalarValueParser<TInternal>,
   // Parses an externally provided literal value to use as an input.

src/utilities/__tests__/extendSchema-test.js

@@ -45,10 +45,7 @@ import {
 } from '../../type';
 
 // Test schema.
-const SomeScalarType = new GraphQLScalarType({
-  name: 'SomeScalar',
-  serialize: x => x,
-});
+const SomeScalarType = new GraphQLScalarType({ name: 'SomeScalar' });
 
 const SomeInterfaceType = new GraphQLInterfaceType({
   name: 'SomeInterface',

src/utilities/__tests__/schemaPrinter-test.js

@@ -405,10 +405,7 @@ describe('Type System Printer', () => {
   });
 
   it('Custom Scalar', () => {
-    const OddType = new GraphQLScalarType({
-      name: 'Odd',
-      serialize() {},
-    });
+    const OddType = new GraphQLScalarType({ name: 'Odd' });
 
     const Schema = new GraphQLSchema({ types: [OddType] });
     const output = printForTest(Schema);

src/utilities/buildASTSchema.js

@@ -12,7 +12,6 @@ import inspect from '../jsutils/inspect';
 import invariant from '../jsutils/invariant';
 import keyMap from '../jsutils/keyMap';
 import keyValMap from '../jsutils/keyValMap';
-import identityFunc from '../jsutils/identityFunc';
 import { type ObjMap } from '../jsutils/ObjMap';
 import { valueFromAST } from './valueFromAST';
 import { assertValidSDL } from '../validation/validate';
@@ -400,7 +399,6 @@ export class ASTDefinitionBuilder {
       name: astNode.name.value,
       description: getDescription(astNode, this._options),
       astNode,
-      serialize: identityFunc,
     });
   }
 

src/utilities/buildClientSchema.js

@@ -11,7 +11,6 @@ import objectValues from '../polyfills/objectValues';
 import inspect from '../jsutils/inspect';
 import invariant from '../jsutils/invariant';
 import keyValMap from '../jsutils/keyValMap';
-import identityFunc from '../jsutils/identityFunc';
 import { valueFromAST } from './valueFromAST';
 import { parseValue } from '../language/parser';
 import {
@@ -231,7 +230,6 @@ export function buildClientSchema(
     return new GraphQLScalarType({
       name: scalarIntrospection.name,
       description: scalarIntrospection.description,
-      serialize: identityFunc,
     });
   }
 

src/validation/__tests__/harness.js

@@ -293,9 +293,6 @@ const ComplicatedArgs = new GraphQLObjectType({
 
 const InvalidScalar = new GraphQLScalarType({
   name: 'Invalid',
-  serialize(value) {
-    return value;
-  },
   parseLiteral(valueNode) {
     throw new Error(`Invalid scalar is always invalid: ${print(valueNode)}`);
   },
@@ -304,12 +301,7 @@ const InvalidScalar = new GraphQLScalarType({
   },
 });
 
-const AnyScalar = new GraphQLScalarType({
-  name: 'Any',
-  serialize(value) {
-    return value;
-  },
-});
+const AnyScalar = new GraphQLScalarType({ name: 'Any' });
 
 const QueryRoot = new GraphQLObjectType({
   name: 'QueryRoot',