chore: use eslint v9 and flat config (#347)

Author: ota-meshi

.eslintignore

@@ -0,0 +1,13 @@
+import base from "./eslint.config.mjs";
+import eslintRuleTester from "eslint-plugin-eslint-rule-tester";
+
+export default [
+  ...base,
+  {
+    files: ["tests/src/rules/**/*.ts"],
+    plugins: { "eslint-rule-tester": eslintRuleTester },
+    rules: {
+      "eslint-rule-tester/valid-testcase": "error",
+    },
+  },
+];

.eslintrc.for-vscode.js

@@ -13,7 +13,7 @@ jobs:
       - uses: actions/checkout@v4
       - uses: actions/setup-node@v4
       - name: Install Packages
-        run: npm install -f
+        run: npm install
       - name: Build
         run: npm run build
       - name: Lint
@@ -52,22 +52,22 @@ jobs:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        node-version: [12.x, 14.x, 16.x, 17.x, 18.x, 20.x]
+        node-version: [18, 20, 22]
     steps:
       - uses: actions/checkout@v4
       - name: Use Node.js ${{ matrix.node-version }}
         uses: actions/setup-node@v4
         with:
           node-version: ${{ matrix.node-version }}
       - name: Install Packages
-        run: npm install -f
+        run: npm install
       - name: Test
         run: npm test
-  test-with-eslint6:
+  test-with-eslint8:
     runs-on: ubuntu-latest
     strategy:
       matrix:
-        node-version: [12.x]
+        node-version: [12.x, 14.x, 16.x, 17.x]
     steps:
       - uses: actions/checkout@v4
       - name: Use Node.js ${{ matrix.node-version }}
@@ -76,22 +76,29 @@ jobs:
           node-version: ${{ matrix.node-version }}
       - name: Install Target Packages
         run: |+
-          npm i -D eslint@6 mocha@7
+          npm i -D eslint@8
           npx rimraf node_modules
           npm install
+      - name: Install Packages
+        run: npm install
       - name: Test
         run: npm test
-  test-with-eslint9:
+  test-with-eslint6:
     runs-on: ubuntu-latest
+    strategy:
+      matrix:
+        node-version: [12.x]
     steps:
       - uses: actions/checkout@v4
-      - name: Use Node.js
+      - name: Use Node.js ${{ matrix.node-version }}
         uses: actions/setup-node@v4
+        with:
+          node-version: ${{ matrix.node-version }}
       - name: Install Target Packages
         run: |+
-          npm i -D eslint@^9.0.0-0 --legacy-peer-deps
+          npm i -D eslint@6 mocha@7
           npx rimraf node_modules
-          npm install --legacy-peer-deps
+          npm install
       - name: Test
         run: npm test
   test-with-eslint7:
@@ -107,18 +114,16 @@ jobs:
           node-version: ${{ matrix.node-version }}
       - name: Install Target Packages
         run: |+
-          npm i -D eslint@7 --legacy-peer-deps
+          npm i -D eslint@7
           npx rimraf node_modules
-          npm install --legacy-peer-deps
+          npm install
       - name: Test
         run: npm test
   test-and-coverage:
     runs-on: ubuntu-latest
     steps:
       - uses: actions/checkout@v4
       - uses: actions/setup-node@v4
-        with:
-          node-version: 14.x
       - name: Install Packages
         run: npm install
       - name: Test

.eslintrc.for-vscode.mjs

@@ -15,7 +15,7 @@ jobs:
         with:
           # This makes Actions fetch all Git history so that Changesets can generate changelogs with the correct commits
           fetch-depth: 0
-      - name: Setup Node.js 16
+      - name: Setup Node.js
         uses: actions/setup-node@v4
       - name: Install Dependencies
         run: npm install -f

.eslintrc.js

@@ -1 +1,2 @@
-package-lock=false
+package-lock=false
+force=true

.github/workflows/NodeCI.yml

@@ -10,7 +10,7 @@
     "yaml"
   ],
   "eslint.options": {
-    "overrideConfigFile": "./.eslintrc.for-vscode.js"
+    "overrideConfigFile": "./.eslintrc.for-vscode.mjs"
   },
   "typescript.validate.enable": true,
   "javascript.validate.enable": false,

.github/workflows/Release.yml

@@ -1,4 +1,6 @@
 // @ts-nocheck
+"use strict";
+
 const getCoreRules = require("./rules");
 
 const allRules = {};

.npmrc

@@ -1,4 +1,6 @@
 // @ts-nocheck
+"use strict";
+
 const getCoreRules = require("./rules");
 
 const rules = {};