WIP test flat config

.eslintignore

@@ -1,3 +1,3 @@
 !/.*
-/build/
-/test-config/
+build/**
+test-config/**

.eslintrc.base.js

@@ -2,6 +2,8 @@
 
 // This file is only used in `./.eslintrc.js` and in the tests – it’s not part
 // of the eslint-config-prettier npm package.
+//
+// NOTE: Keep this file in sync with `./eslint.base.config.js`!
 
 const config = require(".");
 
@@ -40,7 +42,7 @@ module.exports = {
     "indent": "off",
     "linebreak-style": "off",
     "no-dupe-keys": "error",
-    "strict": "error",
+    "strict": ["error", "global"],
     "prefer-spread": "off",
     "require-jsdoc": "off",
     "prettier/prettier": "error",

.eslintrc.js

@@ -5,6 +5,8 @@
 // sharable config from npm and then include the configs exposed by this package
 // as an “eat your own dogfood” test. That feels like a good test, but
 // complicates things a little sometimes.
+//
+// NOTE: Keep this file in sync with `./eslint.config.js`!
 
 module.exports = {
   extends: ["./.eslintrc.base.js", "./index.js", "./prettier.js"],
@@ -32,7 +34,7 @@ module.exports = {
       },
     },
     {
-      files: ["*.test.js"],
+      files: ["**/*.test.js"],
       env: { jest: true },
     },
   ],

.github/workflows/check.yml

@@ -38,9 +38,14 @@ jobs:
         if: steps.cache-node_modules.outputs.cache-hit != 'true'
         run: npm ci --no-audit
 
-      - name: ESLint
+      - name: ESLint – flat
         run: npx eslint .
 
+      - name: ESLint – eslintrc
+        run: npx eslint .
+        env:
+          ESLINT_USE_FLAT_CONFIG: "false"
+
       - name: Prettier
         run: npx prettier --check .
 

README.md

@@ -674,7 +674,8 @@ Finally, you need to mention the plugin in several places:
 
 When you’re done, run `npm test` to verify that you got it all right. It runs several other npm scripts:
 
-- `"test:lint"` makes sure that the files in `test-lint/` pass ESLint when the exclusions from eslint-config-prettier are used. It also lints the code of eslint-config-prettier itself, and checks that Prettier has been run on all files.
+- `"test:prettier"` checks that Prettier has been run on all files.
+- `"test:eslint"` makes sure that the files in `test-lint/` pass ESLint when the exclusions from eslint-config-prettier are used. It also lints the code of eslint-config-prettier itself.
 - `"test:lint-verify-fail"` is run by a test in `test/lint-verify-fail.test.js`.
 - `"test:lint-rules"` is run by a test in `test/rules.test.js`.
 - `"test:jest"` runs unit tests that check a number of things:

eslint.base.config.js

@@ -0,0 +1,93 @@
+"use strict";
+
+// This file is only used in `./eslint.config.js` and in the tests – it’s not part
+// of the eslint-config-prettier npm package.
+//
+// NOTE: Keep this file in sync with `./.eslintrc.base.js`!
+
+const fs = require("fs");
+const path = require("path");
+const babelOld = require("eslint-plugin-babel");
+const babelNew = require("@babel/eslint-plugin");
+const babelParser = require("@babel/eslint-parser");
+const flowtype = require("eslint-plugin-flowtype");
+const globals = require("globals");
+const google = require("eslint-config-google");
+const react = require("eslint-plugin-react");
+const unicorn = require("eslint-plugin-unicorn");
+const vue = require("eslint-plugin-vue");
+const eslintrcBase = require("./.eslintrc.base");
+
+module.exports = [
+  {
+    ignores: fs
+      .readFileSync(path.join(__dirname, ".eslintignore"), "utf8")
+      .trim()
+      .split("\n"),
+  },
+  {
+    // TODO
+    ignores: ["test-lint/flowtype.js"],
+  },
+  google,
+  {
+    plugins: {
+      "babel": babelOld,
+      "@babel": babelNew,
+    },
+  },
+  {
+    plugins: {
+      flowtype,
+    },
+    rules: flowtype.configs.recommended.rules,
+    settings: flowtype.configs.recommended.settings,
+  },
+  {
+    plugins: {
+      react,
+    },
+    rules: react.configs.all.rules,
+  },
+  {
+    plugins: {
+      unicorn,
+    },
+    rules: unicorn.configs.recommended.rules,
+  },
+  {
+    plugins: {
+      vue,
+    },
+    rules: {
+      ...vue.configs.base.rules,
+      ...vue.configs.base.essential,
+      ...vue.configs.base["strongly-recommended"],
+      ...vue.configs.base.recommended,
+    },
+  },
+  {
+    languageOptions: {
+      ecmaVersion: eslintrcBase.parserOptions.ecmaVersion,
+      sourceType: eslintrcBase.parserOptions.sourceType,
+      globals: {
+        ...globals.es6,
+        ...globals.node,
+      },
+      parser: babelParser,
+      parserOptions: {
+        babelOptions: {
+          plugins: [
+            "@babel/plugin-transform-react-jsx",
+            "@babel/plugin-syntax-flow",
+          ],
+        },
+        loggerFn: eslintrcBase.parserOptions.loggerFn,
+        ecmaFeatures: eslintrcBase.parserOptions.ecmaFeatures,
+      },
+    },
+    rules: eslintrcBase.rules,
+    settings: eslintrcBase.settings,
+  },
+  ...eslintrcBase.overrides,
+];

eslint.config.js

@@ -0,0 +1,33 @@
+"use strict";
+
+// This is the internal ESLint config for this project itself – it’s not part of
+// the eslint-config-prettier npm package. The idea here is to extend some
+// sharable config from npm and then include the configs exposed by this package
+// as an “eat your own dogfood” test. That feels like a good test, but
+// complicates things a little sometimes.
+//
+// NOTE: Keep this file in sync with `./.eslintrc.js`!
+
+const globals = require("globals");
+const base = require("./eslint.base.config");
+const index = require(".");
+const prettier = require("./prettier");
+const eslintrc = require("./.eslintrc");
+
+module.exports = [
+  ...base,
+  index,
+  prettier,
+  {
+    rules: eslintrc.rules,
+  },
+  ...eslintrc.overrides.map(({ env = {}, ...override }) => ({
+    ...override,
+    languageOptions: {
+      globals: Object.entries(env).reduce(
+        (acc, [key, enabled]) => (enabled ? { ...acc, ...globals[key] } : acc),
+        {}
+      ),
+    },
+  })),
+];