build: use typescript-eslint@v6 internally

.eslintrc.cjs

@@ -1,8 +1,17 @@
 module.exports = {
-  extends: 'react-app',
+  extends: [
+    'react-app',
+    'plugin:@typescript-eslint/recommended-type-checked',
+    'plugin:@typescript-eslint/stylistic-type-checked'
+  ],
 
   parser: '@typescript-eslint/parser',
 
+  parserOptions: {
+    project: true,
+    tsconfigRootDir: __dirname
+  },
+
   plugins: ['@typescript-eslint'],
 
   settings: {
@@ -20,8 +29,8 @@ module.exports = {
 
   rules: {
     'jsx-a11y/href-no-hash': 'off',
-    'no-unused-vars': 'off',
-    '@typescript-eslint/no-unused-expressions': 'off',
+
+    // These off/not-configured-the-way-we-want lint rules we like & opt into
     '@typescript-eslint/no-unused-vars': [
       'error',
       {
@@ -31,6 +40,33 @@ module.exports = {
         argsIgnorePattern: '^_',
         varsIgnorePattern: '^_'
       }
-    ]
+    ],
+    '@typescript-eslint/restrict-template-expressions': [
+      'error',
+      {
+        allowNever: true
+      }
+    ],
+
+    // Todo: investigate whether we'd like these on
+    '@typescript-eslint/ban-ts-comment': 'off',
+    '@typescript-eslint/ban-types': 'off',
+    '@typescript-eslint/consistent-indexed-object-style': 'off',
+    '@typescript-eslint/consistent-type-definitions': 'off',
+    '@typescript-eslint/no-confusing-void-expression': 'off',
+    '@typescript-eslint/no-empty-function': 'off',
+    '@typescript-eslint/no-floating-promises': 'off',
+    '@typescript-eslint/no-unsafe-argument': 'off',
+    '@typescript-eslint/no-unsafe-assignment': 'off',
+    '@typescript-eslint/no-unsafe-call': 'off',
+    '@typescript-eslint/no-unsafe-member-access': 'off',
+    '@typescript-eslint/no-unsafe-return': 'off',
+    '@typescript-eslint/prefer-function-type': 'off',
+    '@typescript-eslint/sort-type-constituents': 'off',
+    '@typescript-eslint/unbound-method': 'off',
+    'prefer-rest-params': 'off',
+
+    // These lint rules don't make sense for us but are enabled in the preset configs
+    '@typescript-eslint/no-unused-expressions': 'off'
   }
 }

package.json

@@ -59,8 +59,8 @@
   "devDependencies": {
     "@babel/core": "^7.19.0",
     "@types/node": "^18.7.16",
-    "@typescript-eslint/eslint-plugin": "^5.36.2",
-    "@typescript-eslint/parser": "^5.36.2",
+    "@typescript-eslint/eslint-plugin": "6.0.0-alpha.158",
+    "@typescript-eslint/parser": "6.0.0-alpha.158",
     "cross-env": "^7.0.3",
     "esbuild-extra": "^0.1.3",
     "eslint": "^8.23.0",
@@ -78,5 +78,9 @@
     "typescript": "^4.8.3",
     "vitest": "^0.27.2"
   },
+  "resolutions": {
+    "@typescript-eslint/eslint-plugin": "6.0.0-alpha.158",
+    "@typescript-eslint/parser": "6.0.0-alpha.158"
+  },
   "sideEffects": false
 }

src/applyMiddleware.ts

@@ -64,7 +64,7 @@ export default function applyMiddleware(
 
     const middlewareAPI: MiddlewareAPI = {
       getState: store.getState,
-      dispatch: (action, ...args) => dispatch(action, ...args)
+      dispatch: (action, ...args: unknown[]) => dispatch(action, ...args)
     }
     const chain = middlewares.map(middleware => middleware(middlewareAPI))
     dispatch = compose<typeof dispatch>(...chain)(store.dispatch)

src/combineReducers.ts

@@ -125,9 +125,7 @@ export default function combineReducers(reducers: {
 }) {
   const reducerKeys = Object.keys(reducers)
   const finalReducers: { [key: string]: Reducer<any, any, any> } = {}
-  for (let i = 0; i < reducerKeys.length; i++) {
-    const key = reducerKeys[i]
-
+  for (const key of reducerKeys) {
     if (process.env.NODE_ENV !== 'production') {
       if (typeof reducers[key] === 'undefined') {
         warning(`No reducer provided for key "${key}"`)
@@ -176,13 +174,12 @@ export default function combineReducers(reducers: {
 
     let hasChanged = false
     const nextState: StateFromReducersMapObject<typeof reducers> = {}
-    for (let i = 0; i < finalReducerKeys.length; i++) {
-      const key = finalReducerKeys[i]
+    for (const key of finalReducerKeys) {
       const reducer = finalReducers[key]
       const previousStateForKey = state[key]
       const nextStateForKey = reducer(previousStateForKey, action)
       if (typeof nextStateForKey === 'undefined') {
-        const actionType = action && action.type
+        const actionType = action?.type
         throw new Error(
           `When called with an action of type ${
             actionType ? `"${String(actionType)}"` : '(unknown type)'

test/combineReducers.spec.ts

@@ -15,7 +15,7 @@ describe('Utils', () => {
       type PushAction = { type: 'push'; value: unknown }
 
       const reducer = combineReducers({
-        counter: (state: number = 0, action: IncrementAction) =>
+        counter: (state = 0, action: IncrementAction) =>
           action.type === 'increment' ? state + 1 : state,
         stack: (state: any[] = [], action: PushAction) =>
           action.type === 'push' ? [...state, action.value] : state
@@ -64,8 +64,8 @@ describe('Utils', () => {
 
     it('throws an error if a reducer returns undefined handling an action', () => {
       const reducer = combineReducers({
-        counter(state: number = 0, action: Action) {
-          switch (action && action.type) {
+        counter(state = 0, action: Action) {
+          switch (action?.type) {
             case 'increment':
               return state + 1
             case 'decrement':

test/createStore.spec.ts

@@ -431,7 +431,7 @@ describe('createStore', () => {
     const store = createStore(reducers.todos)
 
     let resolve: (value: unknown) => void = () => {}
-    let promise = new Promise(_resolve => {
+    const promise = new Promise(_resolve => {
       resolve = _resolve
     })
     store.subscribe(() => {
@@ -451,7 +451,7 @@ describe('createStore', () => {
   it('does not leak private listeners array', async () => {
     const store = createStore(reducers.todos)
     let resolve: (value: unknown) => void = () => {}
-    let promise = new Promise(_resolve => {
+    const promise = new Promise(_resolve => {
       resolve = _resolve
     })
 

test/typescript/actions.ts

@@ -23,7 +23,7 @@ namespace FreeShapeAction {
     text: 'test'
   }
 
-  const text: string = action['text']
+  const text: string = action.text
 }
 
 namespace StringLiteralTypeAction {

test/typescript/store.ts

@@ -101,10 +101,10 @@ const storeWithCombineReducerAndBadPreloadedState = createStore(
 )
 
 const nestedCombinedReducer = combineReducers({
-  a: (state: string = 'a') => state,
+  a: (state = 'a') => state,
   b: combineReducers({
-    c: (state: string = 'c') => state,
-    d: (state: string = 'd') => state
+    c: (state = 'c') => state,
+    d: (state = 'd') => state
   }),
   e: (state: BrandedString = brandedString) => state
 })
@@ -116,8 +116,8 @@ const storeWithNestedCombineReducer = createStore(nestedCombinedReducer, {
 })
 
 const simpleCombinedReducer = combineReducers({
-  c: (state: string = 'c') => state,
-  d: (state: string = 'd') => state
+  c: (state = 'c') => state,
+  d: (state = 'd') => state
 })
 
 // @ts-expect-error