Use ESLint on .astro and .ts files (withastro#710)

Co-authored-by: Chris Swithinbank <[email protected]>

.eslintignore

@@ -0,0 +1,5 @@
+dist
+node_modules
+.github
+.changeset
+/src/pages/lighthouse

.eslintrc.js

@@ -0,0 +1,33 @@
+module.exports = {
+  env: {
+    node: true,
+    es2022: true,
+    browser: true,
+  },
+  extends: ['eslint:recommended', 'plugin:astro/recommended'],
+  parserOptions: {
+    ecmaVersion: 'latest',
+    sourceType: 'module',
+  },
+  rules: {},
+  overrides: [
+    {
+      files: ["*.astro"],
+      parser: "astro-eslint-parser",
+      parserOptions: {
+        parser: "@typescript-eslint/parser",
+        extraFileExtensions: [".astro"],
+      },
+      rules: {},
+    },
+    {
+      files: ['*.ts'],
+      parser: '@typescript-eslint/parser',
+      extends: ['plugin:@typescript-eslint/recommended'],
+      rules: {
+        '@typescript-eslint/no-unused-vars': ['error', { argsIgnorePattern: '^_', destructuredArrayIgnorePattern: '^_' }],
+        '@typescript-eslint/no-non-null-assertion': 'off',
+      },
+    },
+  ],
+};

package.json

@@ -15,6 +15,7 @@
     "lint:linkcheck": "astro build && tsm --require=./scripts/lib/filter-warnings.cjs ./scripts/lint-linkcheck.ts",
     "lint:linkcheck:nobuild": "tsm --require=./scripts/lib/filter-warnings.cjs ./scripts/lint-linkcheck.ts",
     "lint:slugcheck": "node ./scripts/lint-slugcheck.mjs",
+    "lint:eslint": "eslint . --ext .js,.ts,.astro",
     "github:translation-status": "node ./scripts/github-translation-status.mjs"
   },
   "devDependencies": {
@@ -25,9 +26,14 @@
     "@astrojs/sitemap": "^0.1.0",
     "@babel/core": "^7.17.9",
     "@types/react": "^17.0.43",
+    "@typescript-eslint/eslint-plugin": "^5.27.0",
+    "@typescript-eslint/parser": "^5.27.0",
     "astro": "^1.0.0-beta.17",
+    "astro-eslint-parser": "^0.2.2",
     "bcp-47-normalize": "^2.1.0",
     "dedent-js": "^1.0.1",
+    "eslint": "^8.16.0",
+    "eslint-plugin-astro": "^0.8.1",
     "fast-glob": "^3.2.11",
     "htmlparser2": "^7.2.0",
     "kleur": "^4.1.4",
@@ -38,7 +44,8 @@
     "react": "^17.0.2",
     "react-dom": "^17.0.2",
     "simple-git": "^3.7.1",
-    "tsm": "^2.2.1"
+    "tsm": "^2.2.1",
+    "typescript": "^4.7.2"
   },
   "dependencies": {
     "@astropub/icons": "^0.2.0",