Add Experimental support of Flat Config (#1522)

* feat(client): add eslint.config.js to watch target

* add experimentalUseFlatConfig setting

* Support loading FlatESLint

* add flatConfig playground

* fix

* clean up flatConfig playground

* comment in

* revert unnecessary formatting changes

* fix type and make error message more helpful

* update error message

* improve error message

$shared/settings.ts

@@ -155,6 +155,7 @@ export type ConfigurationSettings = {
 	validate: Validate;
 	packageManager: PackageManagers;
 	useESLintClass: boolean;
+	experimentalUseFlatConfig: boolean;
 	codeAction: CodeActionSettings;
 	codeActionOnSave: CodeActionsOnSaveSettings;
 	format: boolean;

client/src/client.ts

@@ -111,7 +111,7 @@ export namespace ESLintClient {
 
 		// Filters for client options
 		const packageJsonFilter: DocumentFilter = { scheme: 'file', pattern: '**/package.json' };
-		const configFileFilter: DocumentFilter = { scheme: 'file', pattern: '**/.eslintr{c.js,c.yaml,c.yml,c,c.json}' };
+		const configFileFilter: DocumentFilter = { scheme: 'file', pattern: '**/{.eslintr{c.js,c.yaml,c.yml,c,c.json},eslint.config.js}' };
 		const supportedQuickFixKinds: Set<string> = new Set([CodeActionKind.Source.value, CodeActionKind.SourceFixAll.value, `${CodeActionKind.SourceFixAll.value}.eslint`, CodeActionKind.QuickFix.value]);
 
 		// A map of documents synced to the server
@@ -394,6 +394,7 @@ export namespace ESLintClient {
 				synchronize: {
 					fileEvents: [
 						Workspace.createFileSystemWatcher('**/.eslintr{c.js,c.cjs,c.yaml,c.yml,c,c.json}'),
+						Workspace.createFileSystemWatcher('**/eslint.config.js'),
 						Workspace.createFileSystemWatcher('**/.eslintignore'),
 						Workspace.createFileSystemWatcher('**/package.json')
 					]
@@ -604,6 +605,7 @@ export namespace ESLintClient {
 					validate: Validate.off,
 					packageManager: config.get<PackageManagers>('packageManager', 'npm'),
 					useESLintClass: config.get<boolean>('useESLintClass', false),
+					experimentalUseFlatConfig: config.get<boolean>('experimentalUseFlatConfig', false),
 					codeActionOnSave: {
 						mode: CodeActionsOnSaveMode.all
 					},

package.json

@@ -182,6 +182,12 @@
 					"default": false,
 					"description": "Since version 7 ESLint offers a new API call ESLint. Use it even if the old CLIEngine is available. From version 8 on forward on ESLint class is available."
 				},
+				"eslint.experimentalUseFlatConfig": {
+					"scope": "resource",
+					"type": "boolean",
+					"default": false,
+					"description": "Enable support of experimental Flat Config (aka eslint.config.js, supported by ESLint version 8.21 or later)."
+				},
 				"eslint.workingDirectories": {
 					"scope": "resource",
 					"type": "array",

playgrounds/flatConfig/.vscode/settings.json

@@ -0,0 +1,22 @@
+// Place your settings in this file to overwrite default and user settings.
+{
+	"eslint.enable": true,
+	"eslint.run": "onType",
+	"eslint.trace.server": {
+		"verbosity": "messages",
+		"format": "text"
+	},
+	"files.autoSave": "off",
+	"editor.formatOnSave": false,
+	"[javascript]": {
+		"editor.formatOnSave": false,
+		"editor.defaultFormatter": "dbaeumer.vscode-eslint"
+	},
+	"eslint.format.enable": true,
+	"eslint.onIgnoredFiles": "off",
+	"editor.codeActionsOnSave": {
+		"source.fixAll": true,
+		"source.fixAll.eslint": true
+	},
+	"eslint.experimentalUseFlatConfig": true
+}

playgrounds/flatConfig/app.js

@@ -0,0 +1,12 @@
+function bar() {
+	if (foo) {
+		foo++;
+	}
+}
+
+function foo(x) {
+	console.log(x);
+	bar();
+	var x = 10;
+	console.log(undef);
+}

playgrounds/flatConfig/eslint.config.js

@@ -0,0 +1,26 @@
+const globals = require('globals');
+
+module.exports = [
+	"eslint:recommended",
+	{
+		files: ["**/*.js"],
+		languageOptions: {
+			parserOptions: {
+				sourceType: "module"
+			},
+			globals: {
+				...globals.browser,
+				...globals.node,
+				...globals.es6,
+				...globals.commonjs
+			}
+		},
+	},
+	{
+		files: ["sub/*.js"],
+		rules: {
+			"no-undef": "warn",
+			"no-console": "warn"
+		}
+	}
+]