Add support for eslint v9 config files + settings

packages/knip/fixtures/plugins/eslint2/eslint.config.ts

@@ -0,0 +1,19 @@
+import eslint from '@eslint/js';
+import tseslint from 'typescript-eslint';
+
+export default [
+  ...tseslint.config(eslint.configs.recommended, tseslint.configs.recommended),
+  {
+    files: ['**/*.{ts,tsx}'],
+    settings: {
+      'import/parsers': {
+        '@typescript-eslint/parser': ['.ts', '.tsx'],
+      },
+      'import/resolver': {
+        typescript: true,
+        node: true,
+      },
+    },
+    rules: {},
+  },
+];

packages/knip/fixtures/plugins/eslint2/knip.json

@@ -0,0 +1,3 @@
+{
+  "eslint": ["eslint.config.ts"]
+}

packages/knip/fixtures/plugins/eslint2/package.json

@@ -0,0 +1,12 @@
+{
+  "name": "@fixtures/eslint2",
+  "scripts": {
+    "lint": "eslint"
+  },
+  "devDependencies": {
+    "@eslint/js": "*",
+    "eslint": "*",
+    "eslint-import-resolver-typescript": "*",
+    "typescript-eslint": "*"
+  }
+}

packages/knip/src/plugins/eslint/helpers.ts

@@ -2,12 +2,29 @@ import type { PluginOptions } from '../../types/config.js';
 import { compact } from '../../util/array.js';
 import { type ConfigInput, type Input, toConfig, toDeferResolve } from '../../util/input.js';
 import { getPackageNameFromFilePath, getPackageNameFromModuleSpecifier } from '../../util/modules.js';
-import { isAbsolute, isInternal } from '../../util/path.js';
+import { extname, isAbsolute, isInternal } from '../../util/path.js';
 import { getDependenciesFromConfig } from '../babel/index.js';
-import type { ESLintConfig, OverrideConfig } from './types.js';
+import type { ESLintConfig, ESLintConfigDeprecated, OverrideConfigDeprecated } from './types.js';
 
-export const getDependencies = (
-  config: ESLintConfig | OverrideConfig,
+export const getInputs = (
+  config: ESLintConfigDeprecated | OverrideConfigDeprecated | ESLintConfig,
+  options: PluginOptions
+): (Input | ConfigInput)[] => {
+  const { configFileName } = options;
+
+  if (extname(configFileName) === '.json' || !/eslint\.config/.test(configFileName)) {
+    return getInputsDeprecated(config as ESLintConfigDeprecated | OverrideConfigDeprecated, options);
+  }
+
+  const dependencies = (config as ESLintConfig).flatMap(config =>
+    config.settings ? getDependenciesFromSettings(config.settings).filter(id => id !== '@typescript-eslint/parser') : []
+  );
+
+  return compact(dependencies).map(id => toDeferResolve(id));
+};
+
+const getInputsDeprecated = (
+  config: ESLintConfigDeprecated | OverrideConfigDeprecated,
   options: PluginOptions
 ): (Input | ConfigInput)[] => {
   const extendsSpecifiers = config.extends ? compact([config.extends].flat().map(resolveExtendSpecifier)) : [];
@@ -25,9 +42,9 @@ export const getDependencies = (
   const settings = config.settings ? getDependenciesFromSettings(config.settings) : [];
   // const rules = getDependenciesFromRules(config.rules); // TODO enable in next major? Unexpected/breaking in certain cases w/ eslint v8
   const rules = getDependenciesFromRules({});
-  const overrides = config.overrides ? [config.overrides].flat().flatMap(d => getDependencies(d, options)) : [];
-  const x = compact([...extendsSpecifiers, ...plugins, parser, ...settings, ...rules]).map(toDeferResolve);
-  return [...extendConfigs, ...x, ...babelDependencies, ...overrides];
+  const overrides = config.overrides ? [config.overrides].flat().flatMap(d => getInputsDeprecated(d, options)) : [];
+  const deferred = compact([...extendsSpecifiers, ...plugins, parser, ...settings, ...rules]).map(toDeferResolve);
+  return [...extendConfigs, ...deferred, ...babelDependencies, ...overrides];
 };
 
 const isQualifiedSpecifier = (specifier: string) =>
@@ -59,12 +76,12 @@ const resolveExtendSpecifier = (specifier: string) => {
   return resolveSpecifier(namespace, specifier);
 };
 
-const getDependenciesFromRules = (rules: ESLintConfig['rules'] = {}) =>
+const getDependenciesFromRules = (rules: ESLintConfigDeprecated['rules'] = {}) =>
   Object.keys(rules).flatMap(ruleKey =>
     ruleKey.includes('/') ? [resolveSpecifier('eslint-plugin', ruleKey.split('/').slice(0, -1).join('/'))] : []
   );
 
-const getDependenciesFromSettings = (settings: ESLintConfig['settings'] = {}) => {
+const getDependenciesFromSettings = (settings: ESLintConfigDeprecated['settings'] = {}) => {
   return Object.entries(settings).flatMap(([settingKey, settings]) => {
     if (settingKey === 'import/resolver') {
       return (typeof settings === 'string' ? [settings] : Object.keys(settings))

packages/knip/src/plugins/eslint/index.ts

@@ -1,7 +1,7 @@
 import type { IsPluginEnabled, Plugin, ResolveConfig } from '../../types/config.js';
 import { hasDependency } from '../../util/plugin.js';
-import { getDependencies } from './helpers.js';
-import type { ESLintConfig } from './types.js';
+import { getInputs } from './helpers.js';
+import type { ESLintConfigDeprecated } from './types.js';
 
 // New: https://eslint.org/docs/latest/use/configure/configuration-files
 // Old: https://eslint.org/docs/latest/use/configure/configuration-files-deprecated
@@ -24,10 +24,28 @@ const entry = ['eslint.config.{js,cjs,mjs,ts,cts,mts}'];
 
 const config = ['.eslintrc', '.eslintrc.{js,json,cjs}', '.eslintrc.{yml,yaml}', 'package.json'];
 
-const resolveConfig: ResolveConfig<ESLintConfig> = (localConfig, options) => getDependencies(localConfig, options);
+const resolveConfig: ResolveConfig<ESLintConfigDeprecated> = (localConfig, options) => getInputs(localConfig, options);
 
-const note = `For ESLint v8 users: if relying on [configuration cascading](https://eslint.org/docs/v8.x/use/configure/configuration-files#cascading-and-hierarchy),
-consider using something like this:
+const note = `### ESLint v9
+
+Only regular \`import\` statements are considered by default.
+The configuration object is not resolved to find dependencies for \`settings\` such as \`"eslint-import-resolver-typescript"\`.
+To enable this, lift the \`entry\` to a \`config\` file like so:
+
+\`\`\`json
+{
+  "eslint": ["eslint.config.ts"]
+}
+\`\`\`
+
+This is not enabled by default, since this exception may be thrown by a \`@rushstack/eslint-*\` package:
+
+> \`Error: Failed to patch ESLint because the calling module was not recognized.\`
+
+### ESLint v8
+
+If relying on [configuration cascading](https://eslint.org/docs/v8.x/use/configure/configuration-files#cascading-and-hierarchy),
+consider using an extended glob pattern like this:
 
 \`\`\`json
 {

packages/knip/src/plugins/eslint/types.ts

@@ -21,9 +21,11 @@ type BaseConfig = {
   rules?: Rules;
 };
 
-export type OverrideConfig = BaseConfig & { files: string[]; overrides: OverrideConfig };
+export type ESLintConfig = BaseConfig[];
 
-export type ESLintConfig = BaseConfig & {
+export type OverrideConfigDeprecated = BaseConfig & { files: string[]; overrides: OverrideConfigDeprecated };
+
+export type ESLintConfigDeprecated = BaseConfig & {
   env?: Record<string, boolean>;
-  overrides?: OverrideConfig[];
+  overrides?: OverrideConfigDeprecated[];
 };

packages/knip/src/plugins/xo/index.ts

@@ -1,6 +1,6 @@
 import type { IsPluginEnabled, Plugin, ResolveConfig } from '../../types/config.js';
 import { hasDependency } from '../../util/plugin.js';
-import { getDependencies } from '../eslint/helpers.js';
+import { getInputs } from '../eslint/helpers.js';
 import type { XOConfig } from './types.js';
 
 // https://github.com/xojs/xo#config
@@ -18,7 +18,7 @@ const config = ['package.json', '.xo-config', '.xo-config.{js,cjs,json}', 'xo.co
 const entry = ['.xo-config.{js,cjs}', 'xo.config.{js,cjs}'];
 
 const resolveConfig: ResolveConfig<XOConfig> = async (config, options) => {
-  const inputs = getDependencies(config, options);
+  const inputs = getInputs(config, options);
   return [...inputs];
 };
 

packages/knip/src/plugins/xo/types.ts

@@ -1,6 +1,6 @@
-import type { ESLintConfig } from '../eslint/types.js';
+import type { ESLintConfigDeprecated } from '../eslint/types.js';
 
-export type XOConfig = ESLintConfig & {
+export type XOConfig = ESLintConfigDeprecated & {
   envs?: string[] | undefined;
   globals?: string[] | undefined;
   ignores?: string[] | undefined;

packages/knip/test/plugins/eslint2.test.ts

@@ -0,0 +1,21 @@
+import { test } from 'bun:test';
+import assert from 'node:assert/strict';
+import { main } from '../../src/index.js';
+import { resolve } from '../../src/util/path.js';
+import baseArguments from '../helpers/baseArguments.js';
+import baseCounters from '../helpers/baseCounters.js';
+
+const cwd = resolve('fixtures/plugins/eslint2');
+
+test('Find dependencies with the ESLint plugin (2)', async () => {
+  const { counters } = await main({
+    ...baseArguments,
+    cwd,
+  });
+
+  assert.deepEqual(counters, {
+    ...baseCounters,
+    processed: 1,
+    total: 1,
+  });
+});