Update to eslint 9

.eslintignore.root

@@ -1,12 +1,10 @@
-# Named ".eslintignore.root" rather than ".eslintignore" because there's no way to stop eslint from reading this after processing ignorePatterns in .eslintrc.js. Sigh.
+# Our standard eslint config reads .gitignore and .eslintignore to determine what to ignore.
+# This file is named ".eslintignore.root" rather than ".eslintignore" because eslint, despite not using it, still complains if it exists.
 
 # Stuff not to lint in general.
 *.min.js
 **/changelog/
 
-# Storybook files
-**/@(storybook|stories)/**/*.js
-
 # Ignored by default, but we should check it
 !.github/
 !.prettierrc.js

.gitattributes

@@ -17,8 +17,9 @@
 .gitkeep      production-exclude
 
 # We don't need these files in any production mirror.
-.eslintrc.js   production-exclude
-jsconfig.json  production-exclude
-tsconfig.json  production-exclude
-**/.phan/**    production-exclude
+eslint.config.mjs   production-exclude
+.eslintignore       production-exclude
+jsconfig.json       production-exclude
+tsconfig.json       production-exclude
+**/.phan/**         production-exclude
 **/.w.org-assets/** production-exclude

.github/eslint.config.mjs

@@ -0,0 +1,11 @@
+import makeBaseConfig from 'jetpack-js-tools/eslintrc/base.mjs';
+
+export default [
+	...makeBaseConfig( import.meta.url, { envs: [ 'node' ] } ),
+	{
+		rules: {
+			'no-console': 'off',
+			'n/no-process-exit': 'off',
+		},
+	},
+];

.github/workflows/linting.yml

@@ -117,9 +117,9 @@ jobs:
               - 'pnpm-lock.yaml'
               - '.eslintignore'
               - '.eslintignore.root'
-              - '.eslintrc.*'
+              - 'eslint.config.*'
               - '**/.eslintignore'
-              - '**/.eslintrc.*'
+              - '**/eslint.config.*'
               # If the excludelist changed, run to ensure newly non-excluded files pass.
               - 'tools/eslint-excludelist.json'
             misc_excludelist:

.pnpmfile.cjs

@@ -55,6 +55,11 @@ function fixDeps( pkg ) {
 				pkg.peerDependencies[ dep ] = ver.replace( /^\^?/, '>=' );
 			}
 		}
+
+		// Doesn't really need these at all with eslint 9 and our config.
+		pkg.peerDependenciesMeta ??= {};
+		pkg.peerDependenciesMeta[ '@typescript-eslint/eslint-plugin' ] = { optional: true };
+		pkg.peerDependenciesMeta[ '@typescript-eslint/parser' ] = { optional: true };
 	}
 
 	// Unnecessarily explicit deps. I don't think we really even need @wordpress/babel-preset-default at all.

docs/development-environment.md

@@ -364,7 +364,7 @@ To execute them in your local environment, you can use the following commands.
 We strongly recommend that you install tools to review your code in your IDE. It will make it easier for you to notice any missing documentation or coding standards you should respect. Most IDEs display warnings and notices inside the editor, making it even easier.
 
 - Jetpack's custom Code Sniffer ruleset is located at `./projects/packages/codesniffer/Jetpack/ruleset.xml`. Depending on your IDE, you can use this path or you may need to use `.phpcs.xml.dist` in the monorepo root.
-- For JavaScript, we recommend installing ESLint. Most IDEs come with an ESLint plugin that you can use. Jetpack includes a `.eslintrc.js` file that defines our coding standards.
+- For JavaScript, we recommend installing ESLint. Most IDEs come with an ESLint plugin that you can use. Jetpack includes a `eslint.config.mjs` file that defines our coding standards.
 
 ## Linting
 

docs/monorepo.md

@@ -195,17 +195,7 @@ The following environment variables are available for all tests:
 
 We use eslint and phpcs to lint JavaScript and PHP code. Projects should comply with the [coding standards](development-environment.md#coding-standards) enforced by these tools.
 
-* Projects may include `.eslintrc.js` to adjust eslint configuration as necessary, but try to keep to the spirit of it.
-
-  Note we're using something of a hack to get eslint to read ignore rules from `.gitignore` and per-directory `.eslintignore` files.
-  Any eslintrc that does `root: true` or an `extends` that extends from an eslintrc that includes the hack will have to do like
-  ```js
-  const loadIgnorePatterns = require( 'jetpack-js-tools/load-eslint-ignore.js' );
-  module.exports = {
-  	// Whatever stuff, including `root: true` or `extends`.
-  	ignorePatterns: loadIgnorePatterns( __dirname ),
-  };
-  ```
+* Projects may include `eslint.config.mjs` to adjust eslint configuration as necessary, but try to keep to the spirit of it. Configurations should generally start with `...makeBaseConfig( import.meta.url )` (imported from `jetpack-js-tools/eslintrc/base.mjs`) with any appropriate options, and override from there.
 * We're using a fork of phpcs and a custom filter that adds support for per-directory configuration (`.phpcs.dir.xml`) and use of `.gitignore` and `.phpcsignore` files. Again, try to keep to the spirit of things.
 
 ### Static Analysis

eslint.config.mjs

@@ -0,0 +1,3 @@
+import makeBaseConfig from 'jetpack-js-tools/eslintrc/base.mjs';
+
+export default [ ...makeBaseConfig( import.meta.url ) ];

package.json

@@ -17,8 +17,8 @@
 		"cli-setup": "pnpm install && jetpack cli link",
 		"cli-unlink": "jetpack cli unlink",
 		"lint": "pnpm run lint-file .",
-		"lint-changed": "eslint-changed --ext .js,.jsx,.cjs,.mjs,.ts,.tsx,.svelte --git",
-		"lint-file": "eslint --ext .js,.jsx,.cjs,.mjs,.ts,.tsx,.svelte",
+		"lint-changed": "eslint-changed --ext .js,.jsx,.cjs,.mjs,.ts,.tsx,.svelte --eslint-options flags='[\"unstable_config_lookup_from_file\"]' --git",
+		"lint-file": "eslint --flag unstable_config_lookup_from_file",
 		"lint-required": "ESLINT_IGNORE_REQUIRED=1 pnpm run lint --max-warnings=0",
 		"php:autofix": "composer phpcs:fix",
 		"php:compatibility": "composer phpcs:compatibility",
@@ -28,7 +28,7 @@
 		"version-packages": "bash ./tools/version-packages.sh"
 	},
 	"devDependencies": {
-		"eslint": "8.57.1",
+		"eslint": "9.16.0",
 		"husky": "8.0.3",
 		"jetpack-cli": "workspace:*",
 		"jetpack-js-tools": "workspace:*"