[ESLint] enable unicorn/no-useless-undefined

.eslintrc.js

@@ -116,7 +116,7 @@ module.exports = {
     'sonarjs/no-identical-functions': 'error',
     'sonarjs/no-unused-collection': 'error',
     'sonarjs/no-extra-arguments': 'error',
-
+    'unicorn/no-useless-undefined': 'error',
     // Strict Mode (http://eslint.org/docs/rules/#strict-mode)
     strict: 0,
 

packages/cm6-graphql/src/state.ts

@@ -4,10 +4,8 @@ import { GraphQLSchema } from 'graphql';
 import { GqlExtensionsOptions } from './interfaces';
 
 const schemaEffect = StateEffect.define<GraphQLSchema | undefined>();
-const schemaStateField = StateField.define<GraphQLSchema | undefined>({
-  create() {
-    return undefined;
-  },
+const schemaStateField = StateField.define<GraphQLSchema | void>({
+  create() {},
   update(schema, tr) {
     for (const e of tr.effects) {
       if (e.is(schemaEffect)) {
@@ -20,10 +18,8 @@ const schemaStateField = StateField.define<GraphQLSchema | undefined>({
 });
 
 const optionsEffect = StateEffect.define<GqlExtensionsOptions | undefined>();
-const optionsStateField = StateField.define<GqlExtensionsOptions | undefined>({
-  create() {
-    return undefined;
-  },
+const optionsStateField = StateField.define<GqlExtensionsOptions | void>({
+  create() {},
   update(opts, tr) {
     for (const e of tr.effects) {
       if (e.is(optionsEffect)) {

packages/graphiql-react/src/editor/context.tsx

@@ -343,7 +343,7 @@ export function EditorContextProvider(props: EditorContextProviderProps) {
     [storage, tabState, headerEditor],
   );
 
-  const lastShouldPersistHeadersProp = useRef<boolean | undefined>(undefined);
+  const lastShouldPersistHeadersProp = useRef<boolean | undefined>();
   useEffect(() => {
     const propValue = Boolean(props.shouldPersistHeaders);
     if (lastShouldPersistHeadersProp.current !== propValue) {

packages/graphiql-react/src/execution.tsx

@@ -344,7 +344,7 @@ function tryParseJsonObject({
   errorMessageParse: string;
   errorMessageType: string;
 }) {
-  let parsed: Record<string, any> | undefined = undefined;
+  let parsed: Record<string, any> | undefined;
   try {
     parsed = json && json.trim() !== '' ? JSON.parse(json) : undefined;
   } catch (error) {

packages/graphiql/src/components/GraphiQL.tsx

@@ -249,7 +249,7 @@ export function GraphiQLInterface(props: GraphiQLInterfaceProps) {
         props.defaultEditorToolsVisibility === 'variables' ||
         props.defaultEditorToolsVisibility === 'headers'
       ) {
-        return undefined;
+        return;
       }
 
       if (typeof props.defaultEditorToolsVisibility === 'boolean') {

packages/graphql-language-service-server/src/Logger.ts

@@ -63,7 +63,7 @@ export class Logger implements VSCodeLogger {
   }
 
   _log(message: string, severityKey: SeverityEnum): void {
-    const timestamp = new Date().toLocaleString(undefined);
+    const timestamp = new Date().toLocaleString();
     const severity = DIAGNOSTIC_SEVERITY[severityKey];
     const { pid } = process;
 

packages/vscode-graphql-execution/src/helpers/source.ts

@@ -82,7 +82,7 @@ export class SourceHelper {
             JSON.parse(value);
             return null;
           } catch {
-            return undefined;
+            return;
           }
       }
     } catch {