Add eslint

.git-blame-ignore-revs

@@ -2,3 +2,7 @@
 71183da18ae6b0b6b2e8f0c52ea9976232e54f41
 94037fe9c429839f0508ddcd287718b659276e3b
 f51bf4d8907307ace083a0decb34668176c7fad3
+
+# lint fixes
+8bff3b8ad57516e9816278b77ff5e0fffafd85ca
+aeec38a6ef56bb534ff8bc968b95107ff54959cc

.github/actions/ci-checks/action.yml

@@ -6,6 +6,10 @@ runs:
       run: pnpm build
       shell: bash
 
+    - name: ESLint
+      run: pnpm lint --no-cache
+      shell: bash
+
     - name: Typecheck
       run: pnpm typecheck
       shell: bash

.gitignore

@@ -1,3 +1,6 @@
+# eslint
+.eslintcache
+
 # Logs
 logs
 *.log

babel.config.js

@@ -1,6 +1,3 @@
-const { NODE_ENV } = process.env;
-const isTest = NODE_ENV === 'test';
-
 module.exports = {
   assumptions: {
     constantReexports: true, // only matters for tests (since only there we transpile to CJS using Babel), it makes debugging easier

eslint.config.mjs

@@ -0,0 +1,90 @@
+// @ts-check
+import globals from 'globals';
+import js from '@eslint/js';
+import ts from 'typescript-eslint';
+
+export default ts.config(
+  // plugins
+  js.configs.recommended,
+  ...ts.configs.recommendedTypeChecked,
+
+  // global ignore
+  {
+    ignores: [
+      '{docs,examples,templates}/',
+      '**/dist',
+      '**/*.test.*',
+      'scripts/jest-utils/'
+    ]
+  },
+
+  // global language and linter options
+  {
+    languageOptions: {
+      globals: { ...globals.browser, ...globals.node },
+      parserOptions: {
+        projectService: true,
+        tsconfigRootDir: import.meta.dirname
+      }
+    },
+    linterOptions: {
+      reportUnusedDisableDirectives: 'error'
+    }
+  },
+
+  // global rule overrides
+  {
+    rules: {
+      '@typescript-eslint/no-empty-object-type': [
+        'error',
+        {
+          allowInterfaces: 'with-single-extends',
+          allowObjectTypes: 'always'
+        }
+      ],
+      '@typescript-eslint/no-explicit-any': '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/no-unused-vars': [
+        'error',
+        {
+          args: 'all',
+          argsIgnorePattern: '^_',
+          caughtErrors: 'all',
+          caughtErrorsIgnorePattern: '^_',
+          destructuredArrayIgnorePattern: '^_',
+          varsIgnorePattern: '^_',
+          ignoreRestSiblings: true
+        }
+      ],
+      '@typescript-eslint/unbound-method': 'off',
+      '@typescript-eslint/no-redundant-type-constituents': 'off',
+      'prefer-const': [
+        'error',
+        {
+          destructuring: 'all'
+        }
+      ]
+    }
+  },
+
+  // disable type-checking for js files
+  {
+    files: ['**/*.{js,cjs,mjs}'],
+    ...ts.configs.disableTypeChecked
+  },
+
+  // js-specific config and rules
+  {
+    files: ['**/*.{js,cjs}'],
+    languageOptions: {
+      sourceType: 'commonjs'
+    },
+    rules: {
+      '@typescript-eslint/no-require-imports': 'off'
+    }
+  }
+);

package.json

@@ -27,6 +27,7 @@
     "postinstall": "manypkg check && preconstruct dev",
     "build": "preconstruct build",
     "fix": "manypkg fix",
+    "lint": "eslint --cache --quiet",
     "typecheck": "tsc",
     "test": "jest",
     "test:core": "jest packages/core",
@@ -52,6 +53,7 @@
     "@babel/preset-typescript": "^7.23.3",
     "@changesets/changelog-github": "^0.4.8",
     "@changesets/cli": "^2.26.2",
+    "@eslint/js": "^9.7.0",
     "@jest/types": "^29.6.3",
     "@manypkg/cli": "^0.21.4",
     "@preconstruct/cli": "^2.8.1",
@@ -62,6 +64,8 @@
     "@vue/vue3-jest": "^29.2.6",
     "babel-jest": "^29.7.0",
     "babel-preset-solid": "^1.8.4",
+    "eslint": "^9.7.0",
+    "globals": "^15.8.0",
     "husky": "^3.1.0",
     "jest": "^29.7.0",
     "jest-config": "^29.7.0",
@@ -76,6 +80,7 @@
     "svelte-jester": "^2.3.2",
     "synckit": "^0.8.5",
     "typescript": "^5.6.2",
+    "typescript-eslint": "^8.0.1",
     "vue": "^3.0.11"
   },
   "husky": {

packages/core/src/SimulatedClock.ts

@@ -1,5 +1,6 @@
 import { Clock } from './system.ts';
 
+// eslint-disable-next-line @typescript-eslint/no-unsafe-declaration-merging
 export interface SimulatedClock extends Clock {
   start(speed: number): void;
   increment(ms: number): void;
@@ -11,6 +12,7 @@ interface SimulatedTimeout {
   timeout: number;
   fn: (...args: any[]) => void;
 }
+// eslint-disable-next-line @typescript-eslint/no-unsafe-declaration-merging
 export class SimulatedClock implements SimulatedClock {
   private timeouts: Map<number, SimulatedTimeout> = new Map();
   private _now: number = 0;

packages/core/src/State.ts

@@ -19,8 +19,7 @@ import type {
   MetaObject,
   StateSchema,
   StateId,
-  SnapshotStatus,
-  SnapshotFrom
+  SnapshotStatus
 } from './types.ts';
 import { matchesState } from './utils.ts';
 
@@ -37,10 +36,7 @@ type ToTestStateValue<TStateValue extends StateValue> =
               >;
             };
 
-export function isMachineSnapshot<
-  TContext extends MachineContext,
-  TEvent extends EventObject
->(value: unknown): value is AnyMachineSnapshot {
+export function isMachineSnapshot(value: unknown): value is AnyMachineSnapshot {
   return (
     !!value &&
     typeof value === 'object' &&

packages/core/src/StateMachine.ts

@@ -95,7 +95,7 @@ export class StateMachine<
   public implementations: MachineImplementationsSimplified<TContext, TEvent>;
 
   /** @internal */
-  public __xstatenode: true = true;
+  public __xstatenode = true as const;
 
   /** @internal */
   public idMap: Map<string, StateNode<TContext, TEvent>> = new Map();
@@ -559,8 +559,7 @@ export class StateMachine<
     > = (snapshot as any).children;
 
     Object.keys(snapshotChildren).forEach((actorId) => {
-      const actorData =
-        snapshotChildren[actorId as keyof typeof snapshotChildren];
+      const actorData = snapshotChildren[actorId];
       const childState = actorData.snapshot;
       const src = actorData.src;
 
@@ -603,7 +602,7 @@ export class StateMachine<
       TConfig
     >;
 
-    let seen = new Set();
+    const seen = new Set();
 
     function reviveContext(
       contextPart: Record<string, unknown>,
@@ -613,7 +612,7 @@ export class StateMachine<
         return;
       }
       seen.add(contextPart);
-      for (let key in contextPart) {
+      for (const key in contextPart) {
         const value: unknown = contextPart[key];
 
         if (value && typeof value === 'object') {

packages/core/src/StateNode.ts

@@ -186,7 +186,7 @@ export class StateNode<
             (stateConfig: AnyStateNodeConfig, key) => {
               const stateNode = new StateNode(stateConfig, {
                 _parent: this,
-                _key: key as string,
+                _key: key,
                 _machine: this.machine
               });
               return stateNode;
@@ -247,9 +247,9 @@ export class StateNode<
             eventType: null as any,
             reenter: false,
             toJSON: () => ({
-              target: this.initial!.target!.map((t) => `#${t.id}`),
+              target: this.initial.target.map((t) => `#${t.id}`),
               source: `#${this.id}`,
-              actions: this.initial!.actions.map(toSerializableAction),
+              actions: this.initial.actions.map(toSerializableAction),
               eventType: null as any
             })
           }

packages/core/src/actions/assign.ts

@@ -166,8 +166,8 @@ export function assign<
   }
 
   function assign(
-    args: ActionArgs<TContext, TExpressionEvent, TEvent>,
-    params: TParams
+    _args: ActionArgs<TContext, TExpressionEvent, TEvent>,
+    _params: TParams
   ) {
     if (isDevelopment) {
       throw new Error(`This isn't supposed to be called`);

packages/core/src/actions/cancel.ts

@@ -1,7 +1,6 @@
 import isDevelopment from '#is-development';
 import {
   AnyActorScope,
-  AnyActor,
   AnyMachineSnapshot,
   EventObject,
   MachineContext,
@@ -89,8 +88,8 @@ export function cancel<
   sendId: ResolvableSendId<TContext, TExpressionEvent, TParams, TEvent>
 ): CancelAction<TContext, TExpressionEvent, TParams, TEvent> {
   function cancel(
-    args: ActionArgs<TContext, TExpressionEvent, TEvent>,
-    params: TParams
+    _args: ActionArgs<TContext, TExpressionEvent, TEvent>,
+    _params: TParams
   ) {
     if (isDevelopment) {
       throw new Error(`This isn't supposed to be called`);

packages/core/src/actions/emit.ts

@@ -32,11 +32,6 @@ function resolveEmit(
         >;
   }
 ) {
-  if (isDevelopment && typeof eventOrExpr === 'string') {
-    throw new Error(
-      `Only event objects may be used with emit; use emit({ type: "${eventOrExpr}" }) instead`
-    );
-  }
   const resolvedEvent =
     typeof eventOrExpr === 'function'
       ? eventOrExpr(args, actionParams)
@@ -137,8 +132,8 @@ export function emit<
   }
 
   function emit(
-    args: ActionArgs<TContext, TExpressionEvent, TEvent>,
-    params: TParams
+    _args: ActionArgs<TContext, TExpressionEvent, TEvent>,
+    _params: TParams
   ) {
     if (isDevelopment) {
       throw new Error(`This isn't supposed to be called`);

packages/core/src/actions/enqueueActions.ts

@@ -311,8 +311,8 @@ export function enqueueActions<
   TEmitted
 > {
   function enqueueActions(
-    args: ActionArgs<TContext, TExpressionEvent, TEvent>,
-    params: unknown
+    _args: ActionArgs<TContext, TExpressionEvent, TEvent>,
+    _params: unknown
   ) {
     if (isDevelopment) {
       throw new Error(`This isn't supposed to be called`);

packages/core/src/actions/log.ts

@@ -81,8 +81,8 @@ export function log<
   label?: string
 ): LogAction<TContext, TExpressionEvent, TParams, TEvent> {
   function log(
-    args: ActionArgs<TContext, TExpressionEvent, TEvent>,
-    params: TParams
+    _args: ActionArgs<TContext, TExpressionEvent, TEvent>,
+    _params: TParams
   ) {
     if (isDevelopment) {
       throw new Error(`This isn't supposed to be called`);

packages/core/src/actions/raise.ts

@@ -52,6 +52,7 @@ function resolveRaise(
 
   if (typeof eventOrExpr === 'string') {
     throw new Error(
+      // eslint-disable-next-line @typescript-eslint/restrict-template-expressions
       `Only event objects may be used with raise; use raise({ type: "${eventOrExpr}" }) instead`
     );
   }
@@ -149,8 +150,8 @@ export function raise<
   }
 
   function raise(
-    args: ActionArgs<TContext, TExpressionEvent, TEvent>,
-    params: TParams
+    _args: ActionArgs<TContext, TExpressionEvent, TEvent>,
+    _params: TParams
   ) {
     if (isDevelopment) {
       throw new Error(`This isn't supposed to be called`);

packages/core/src/actions/send.ts

@@ -68,6 +68,7 @@ function resolveSendTo(
 
   if (typeof eventOrExpr === 'string') {
     throw new Error(
+      // eslint-disable-next-line @typescript-eslint/restrict-template-expressions
       `Only event objects may be used with sendTo; use sendTo({ type: "${eventOrExpr}" }) instead`
     );
   }
@@ -92,9 +93,12 @@ function resolveSendTo(
   let targetActorRef: AnyActorRef | string | undefined;
 
   if (typeof resolvedTarget === 'string') {
+    // eslint-disable-next-line @typescript-eslint/no-unsafe-enum-comparison
     if (resolvedTarget === SpecialTargets.Parent) {
       targetActorRef = actorScope.self._parent;
-    } else if (resolvedTarget === SpecialTargets.Internal) {
+    }
+    // eslint-disable-next-line @typescript-eslint/no-unsafe-enum-comparison
+    else if (resolvedTarget === SpecialTargets.Internal) {
       targetActorRef = actorScope.self;
     } else if (resolvedTarget.startsWith('#_')) {
       // SCXML compatibility: https://www.w3.org/TR/scxml/#SCXMLEventProcessor
@@ -162,7 +166,7 @@ function executeSendTo(
       actorScope.self,
       // at this point, in a deferred task, it should already be mutated by retryResolveSendTo
       // if it initially started as a string
-      to as Exclude<typeof to, string>,
+      to,
       event.type === XSTATE_ERROR
         ? createErrorActorEvent(actorScope.self.id, (event as any).data)
         : event
@@ -242,8 +246,8 @@ export function sendTo<
   }
 
   function sendTo(
-    args: ActionArgs<TContext, TExpressionEvent, TEvent>,
-    params: TParams
+    _args: ActionArgs<TContext, TExpressionEvent, TEvent>,
+    _params: TParams
   ) {
     if (isDevelopment) {
       throw new Error(`This isn't supposed to be called`);