Use nullish coalescing operator in all appropriate places

src/__tests__/starWarsData.js

@@ -117,7 +117,7 @@ export type Droid = {|
  */
 function getCharacter(id) {
   // Returning a promise just to illustrate that GraphQL.js supports it.
-  return Promise.resolve(humanData[id] || droidData[id]);
+  return Promise.resolve(humanData[id] ?? droidData[id]);
 }
 
 /**

src/error/GraphQLError.js

@@ -148,7 +148,7 @@ export class GraphQLError extends Error {
       locations: {
         // Coercing falsy values to undefined ensures they will not be included
         // in JSON.stringify() when not provided.
-        value: _locations || undefined,
+        value: _locations ?? undefined,
         // By being enumerable, JSON.stringify will include `locations` in the
         // resulting output. This ensures that the simplest possible GraphQL
         // service adheres to the spec.
@@ -157,28 +157,28 @@ export class GraphQLError extends Error {
       path: {
         // Coercing falsy values to undefined ensures they will not be included
         // in JSON.stringify() when not provided.
-        value: path || undefined,
+        value: path ?? undefined,
         // By being enumerable, JSON.stringify will include `path` in the
         // resulting output. This ensures that the simplest possible GraphQL
         // service adheres to the spec.
         enumerable: path != null,
       },
       nodes: {
-        value: _nodes || undefined,
+        value: _nodes ?? undefined,
       },
       source: {
-        value: _source || undefined,
+        value: _source ?? undefined,
       },
       positions: {
-        value: _positions || undefined,
+        value: _positions ?? undefined,
       },
       originalError: {
         value: originalError,
       },
       extensions: {
         // Coercing falsy values to undefined ensures they will not be included
         // in JSON.stringify() when not provided.
-        value: _extensions || undefined,
+        value: _extensions ?? undefined,
         // By being enumerable, JSON.stringify will include `path` in the
         // resulting output. This ensures that the simplest possible GraphQL
         // service adheres to the spec.

src/error/formatError.js

@@ -12,7 +12,7 @@ import { type GraphQLError } from './GraphQLError';
  */
 export function formatError(error: GraphQLError): GraphQLFormattedError {
   devAssert(error, 'Received null or undefined error.');
-  const message = error.message || 'An unknown error occurred.';
+  const message = error.message ?? 'An unknown error occurred.';
   const locations = error.locations;
   const path = error.path;
   const extensions = error.extensions;

src/error/locatedError.js

@@ -22,7 +22,7 @@ export function locatedError(
 
   return new GraphQLError(
     originalError.message,
-    (originalError: any).nodes || nodes,
+    (originalError: any).nodes ?? nodes,
     (originalError: any).source,
     (originalError: any).positions,
     path,

src/execution/execute.js

@@ -314,12 +314,12 @@ export function buildExecutionContext(
   }
 
   /* istanbul ignore next (See https://github.com/graphql/graphql-js/issues/2203) */
-  const variableDefinitions = operation.variableDefinitions || [];
+  const variableDefinitions = operation.variableDefinitions ?? [];
 
   const coercedVariableValues = getVariableValues(
     schema,
     variableDefinitions,
-    rawVariableValues || {},
+    rawVariableValues ?? {},
     { maxErrors: 50 },
   );
 
@@ -334,8 +334,8 @@ export function buildExecutionContext(
     contextValue,
     operation,
     variableValues: coercedVariableValues.coerced,
-    fieldResolver: fieldResolver || defaultFieldResolver,
-    typeResolver: typeResolver || defaultTypeResolver,
+    fieldResolver: fieldResolver ?? defaultFieldResolver,
+    typeResolver: typeResolver ?? defaultTypeResolver,
     errors: [],
   };
 }
@@ -619,7 +619,7 @@ function resolveField(
     return;
   }
 
-  const resolveFn = fieldDef.resolve || exeContext.fieldResolver;
+  const resolveFn = fieldDef.resolve ?? exeContext.fieldResolver;
 
   const info = buildResolveInfo(
     exeContext,
@@ -961,7 +961,7 @@ function completeAbstractValue(
   path: Path,
   result: mixed,
 ): PromiseOrValue<ObjMap<mixed>> {
-  const resolveTypeFn = returnType.resolveType || exeContext.typeResolver;
+  const resolveTypeFn = returnType.resolveType ?? exeContext.typeResolver;
   const contextValue = exeContext.contextValue;
   const runtimeType = resolveTypeFn(result, contextValue, info, returnType);
 

src/execution/values.js

@@ -166,7 +166,7 @@ export function getArgumentValues(
   const coercedValues = {};
 
   /* istanbul ignore next (See https://github.com/graphql/graphql-js/issues/2203) */
-  const argumentNodes = node.arguments || [];
+  const argumentNodes = node.arguments ?? [];
   const argNodeMap = keyMap(argumentNodes, arg => arg.name.value);
 
   for (const argDef of def.args) {

src/language/lexer.js

@@ -66,7 +66,7 @@ export class Lexer {
     if (token.kind !== TokenKind.EOF) {
       do {
         // Note: next is only mutable during parsing, so we cast to allow this.
-        token = token.next || ((token: any).next = readToken(this, token));
+        token = token.next ?? ((token: any).next = readToken(this, token));
       } while (token.kind === TokenKind.COMMENT);
     }
     return token;

src/language/parser.js

@@ -1482,7 +1482,7 @@ class Parser {
    * is encountered.
    */
   unexpected(atToken?: ?Token): GraphQLError {
-    const token = atToken || this._lexer.token;
+    const token = atToken ?? this._lexer.token;
     return syntaxError(
       this._lexer.source,
       token.start,

src/language/printer.js

@@ -256,7 +256,7 @@ function addDescription(cb) {
  * print all items together separated by separator if provided
  */
 function join(maybeArray: ?Array<string>, separator = '') {
-  return maybeArray?.filter(x => x).join(separator) || '';
+  return maybeArray?.filter(x => x).join(separator) ?? '';
 }
 
 /**

src/language/visitor.js

@@ -332,7 +332,7 @@ export function visit(
     } else {
       stack = { inArray, index, keys, edits, prev: stack };
       inArray = Array.isArray(node);
-      keys = inArray ? node : visitorKeys[node.kind] || [];
+      keys = inArray ? node : visitorKeys[node.kind] ?? [];
       index = -1;
       edits = [];
       if (parent) {

src/subscription/subscribe.js

@@ -251,7 +251,7 @@ export function createSourceEventStream(
 
     // Call the `subscribe()` resolver or the default resolver to produce an
     // AsyncIterable yielding raw payloads.
-    const resolveFn = fieldDef.subscribe || exeContext.fieldResolver;
+    const resolveFn = fieldDef.subscribe ?? exeContext.fieldResolver;
 
     const path = addPath(undefined, responseName);
 

src/type/definition.js

@@ -575,13 +575,13 @@ export class GraphQLScalarType {
   extensionASTNodes: ?$ReadOnlyArray<ScalarTypeExtensionNode>;
 
   constructor(config: $ReadOnly<GraphQLScalarTypeConfig<mixed, mixed>>): void {
-    const parseValue = config.parseValue || identityFunc;
+    const parseValue = config.parseValue ?? identityFunc;
     this.name = config.name;
     this.description = config.description;
-    this.serialize = config.serialize || identityFunc;
+    this.serialize = config.serialize ?? identityFunc;
     this.parseValue = parseValue;
     this.parseLiteral =
-      config.parseLiteral || (node => parseValue(valueFromASTUntyped(node)));
+      config.parseLiteral ?? (node => parseValue(valueFromASTUntyped(node)));
     this.extensions = config.extensions && toObjMap(config.extensions);
     this.astNode = config.astNode;
     this.extensionASTNodes = undefineIfEmpty(config.extensionASTNodes);
@@ -777,7 +777,7 @@ function defineInterfaces(
     | GraphQLInterfaceTypeConfig<mixed, mixed>,
   >,
 ): Array<GraphQLInterfaceType> {
-  const interfaces = resolveThunk(config.interfaces) || [];
+  const interfaces = resolveThunk(config.interfaces) ?? [];
   devAssert(
     Array.isArray(interfaces),
     `${config.name} interfaces must be an Array or a function which returns an Array.`,
@@ -812,7 +812,7 @@ function defineFieldMap<TSource, TContext>(
         `provided, but got: ${inspect(fieldConfig.resolve)}.`,
     );
 
-    const argsConfig = fieldConfig.args || {};
+    const argsConfig = fieldConfig.args ?? {};
     devAssert(
       isPlainObj(argsConfig),
       `${config.name}.${fieldName} args must be an object with argument names as keys.`,

src/type/directives.js

@@ -65,7 +65,7 @@ export class GraphQLDirective {
     this.name = config.name;
     this.description = config.description;
     this.locations = config.locations;
-    this.isRepeatable = config.isRepeatable || false;
+    this.isRepeatable = config.isRepeatable ?? false;
     this.extensions = config.extensions && toObjMap(config.extensions);
     this.astNode = config.astNode;
 
@@ -75,7 +75,7 @@ export class GraphQLDirective {
       `@${config.name} locations must be an Array.`,
     );
 
-    const args = config.args || {};
+    const args = config.args ?? {};
     devAssert(
       isObjectLike(args) && !Array.isArray(args),
       `@${config.name} args must be an object with argument names as keys.`,

src/type/schema.js

@@ -167,7 +167,7 @@ export class GraphQLSchema {
     this._mutationType = config.mutation;
     this._subscriptionType = config.subscription;
     // Provide specified directives (e.g. @include and @skip) by default.
-    this._directives = config.directives || specifiedDirectives;
+    this._directives = config.directives ?? specifiedDirectives;
 
     // To preserve order of user-provided types, we add first to add them to
     // the set of "collected" types, so `collectReferencedTypes` ignore them.
@@ -289,7 +289,7 @@ export class GraphQLSchema {
     interfaces: /* $ReadOnly */ Array<GraphQLInterfaceType>,
   |} {
     const implementations = this._implementationsMap[interfaceType.name];
-    return implementations || { objects: [], interfaces: [] };
+    return implementations ?? { objects: [], interfaces: [] };
   }
 
   // @deprecated: use isSubType instead - will be removed in v16.

src/type/validate.js

@@ -188,7 +188,7 @@ function validateName(
   node: { +name: string, +astNode: ?ASTNode, ... },
 ): void {
   // Ensure names are valid, however introspection types opt out.
-  const error = isValidNameError(node.name, node.astNode || undefined);
+  const error = isValidNameError(node.name, node.astNode ?? undefined);
   if (error) {
     context.addError(error);
   }
@@ -578,15 +578,15 @@ function getAllNodes<T: ASTNode, K: ASTNode>(
     ? extensionASTNodes
       ? [astNode].concat(extensionASTNodes)
       : [astNode]
-    : extensionASTNodes || [];
+    : extensionASTNodes ?? [];
 }
 
 function getAllSubNodes<T: ASTNode, K: ASTNode, L: ASTNode>(
   object: SDLDefinedObject<T, K>,
   getter: (T | K) => ?(L | $ReadOnlyArray<L>),
 ): $ReadOnlyArray<L> {
   /* istanbul ignore next (See https://github.com/graphql/graphql-js/issues/2203) */
-  return flatMap(getAllNodes(object), item => getter(item) || []);
+  return flatMap(getAllNodes(object), item => getter(item) ?? []);
 }
 
 function getAllImplementsInterfaceNodes(

src/utilities/TypeInfo.js

@@ -77,7 +77,7 @@ export class TypeInfo {
     this._directive = null;
     this._argument = null;
     this._enumValue = null;
-    this._getFieldDef = getFieldDefFn || getFieldDef;
+    this._getFieldDef = getFieldDefFn ?? getFieldDef;
     if (initialType) {
       if (isInputType(initialType)) {
         this._inputTypeStack.push(initialType);
@@ -205,7 +205,7 @@ export class TypeInfo {
       case Kind.ARGUMENT: {
         let argDef;
         let argType: mixed;
-        const fieldOrDirective = this.getDirective() || this.getFieldDef();
+        const fieldOrDirective = this.getDirective() ?? this.getFieldDef();
         if (fieldOrDirective) {
           argDef = find(
             fieldOrDirective.args,

src/utilities/__tests__/buildASTSchema-test.js

@@ -11,6 +11,7 @@ import { parse } from '../../language/parser';
 import { print } from '../../language/printer';
 
 import { validateSchema } from '../../type/validate';
+import { __Schema } from '../../type/introspection';
 import {
   assertDirective,
   GraphQLSkipDirective,
@@ -43,10 +44,11 @@ import { buildASTSchema, buildSchema } from '../buildASTSchema';
  * the SDL, parsed in a schema AST, materializing that schema AST into an
  * in-memory GraphQLSchema, and then finally printing that object into the SDL
  */
-function cycleSDL(sdl, options = {}) {
-  const commentDescriptions = options.commentDescriptions || false;
+function cycleSDL(sdl, options) {
   const ast = parse(sdl);
   const schema = buildASTSchema(ast, options);
+
+  const commentDescriptions = options?.commentDescriptions;
   return printSchema(schema, { commentDescriptions });
 }
 
@@ -1046,6 +1048,20 @@ describe('Schema Builder', () => {
     expect(errors).to.have.lengthOf.above(0);
   });
 
+  it('Do not override standard types', () => {
+    // NOTE: not sure it's desired behaviour to just silently ignore override
+    // attempts so just documenting it here.
+
+    const schema = buildSchema(`
+      scalar ID
+
+      scalar __Schema
+    `);
+
+    expect(schema.getType('ID')).to.equal(GraphQLID);
+    expect(schema.getType('__Schema')).to.equal(__Schema);
+  });
+
   it('Rejects invalid SDL', () => {
     const sdl = `
       type Query {

src/utilities/__tests__/stripIgnoredCharacters-test.js

@@ -69,7 +69,7 @@ function lexValue(str) {
 // Called only to make error messages for failing tests
 /* istanbul ignore next */
 function inspectStr(str) {
-  return (JSON.stringify(str) || '')
+  return (JSON.stringify(str) ?? '')
     .replace(/^"|"$/g, '`')
     .replace(/\\"/g, '"');
 }

src/utilities/buildASTSchema.js

@@ -123,17 +123,16 @@ export function buildSchema(
   options?: {| ...BuildSchemaOptions, ...ParseOptions |},
 ): GraphQLSchema {
   const document = parse(source, {
-    noLocation: options?.noLocation || false,
-    allowLegacySDLEmptyFields: options?.allowLegacySDLEmptyFields || false,
+    noLocation: options?.noLocation,
+    allowLegacySDLEmptyFields: options?.allowLegacySDLEmptyFields,
     allowLegacySDLImplementsInterfaces:
-      options?.allowLegacySDLImplementsInterfaces || false,
-    experimentalFragmentVariables:
-      options?.experimentalFragmentVariables || false,
+      options?.allowLegacySDLImplementsInterfaces,
+    experimentalFragmentVariables: options?.experimentalFragmentVariables,
   });
 
   return buildASTSchema(document, {
-    commentDescriptions: options?.commentDescriptions || false,
-    assumeValidSDL: options?.assumeValidSDL || false,
-    assumeValid: options?.assumeValid || false,
+    commentDescriptions: options?.commentDescriptions,
+    assumeValidSDL: options?.assumeValidSDL,
+    assumeValid: options?.assumeValid,
   });
 }