fix: Resolve config modules with ESM createRequire()

ES modules do not have require() available, we must construct it first.
This fixes the CLI when passing `--config my-config-package`, broken in
v12.0.0.

The tests didn't catch this because Jest still doesn't support mocking
ESM, and there's really no way to write a test for this right now.

I wasn't able to get the automatic `test/__mocks__/resolveConfig.js` to
work, probably a race condition between the module parser and the mocker.

jest.config.js

@@ -1,6 +1,11 @@
 const config = {
   collectCoverage: true,
-  collectCoverageFrom: ['lib/**/*.js'],
+  collectCoverageFrom: [
+    'lib/**/*.js',
+    // Avoid ESM import.meta parse error.
+    // (Can't measure coverage anyway, it's always mocked)
+    '!lib/resolveConfig.js',
+  ],
   moduleDirectories: ['node_modules'],
   setupFiles: ['./testSetup.js'],
   snapshotSerializers: ['jest-snapshot-serializer-ansi'],

lib/loadConfig.js

@@ -6,6 +6,8 @@ import debug from 'debug'
 import { lilconfig } from 'lilconfig'
 import YAML from 'yaml'
 
+import { resolveConfig } from './resolveConfig'
+
 const debugLog = debug('lint-staged:loadConfig')
 
 /**
@@ -49,14 +51,6 @@ const loaders = {
   noExt: yamlParse,
 }
 
-const resolveConfig = (configPath) => {
-  try {
-    return require.resolve(configPath)
-  } catch {
-    return configPath
-  }
-}
-
 /**
  * @param {object} options
  * @param {string} [options.configPath] - Explicit path to a config file

lib/resolveConfig.js

@@ -0,0 +1,15 @@
+import { createRequire } from 'module'
+
+/**
+ * require() does not exist for ESM, so we must create it to use require.resolve().
+ * @see https://nodejs.org/api/module.html#modulecreaterequirefilename
+ */
+const require = createRequire(import.meta.url)
+
+export function resolveConfig(configPath) {
+  try {
+    return require.resolve(configPath)
+  } catch {
+    return configPath
+  }
+}

test/index.spec.js

@@ -28,6 +28,16 @@ jest.mock('url', () => ({
 
 jest.mock('../lib/getStagedFiles')
 jest.mock('../lib/gitWorkflow')
+jest.mock('../lib/resolveConfig', () => ({
+  /** Unfortunately necessary due to non-ESM tests. */
+  resolveConfig: (configPath) => {
+    try {
+      return require.resolve(configPath)
+    } catch {
+      return configPath
+    }
+  },
+}))
 jest.mock('../lib/validateOptions', () => ({
   validateOptions: jest.fn().mockImplementation(async () => {}),
 }))

test/index2.spec.js

@@ -4,6 +4,17 @@ import { Listr } from 'listr2'
 import makeConsoleMock from 'consolemock'
 
 jest.mock('listr2')
+jest.mock('../lib/resolveConfig', () => ({
+  /** Unfortunately necessary due to non-ESM tests. */
+  resolveConfig: (configPath) => {
+    try {
+      return require.resolve(configPath)
+    } catch {
+      return configPath
+    }
+  },
+}))
+
 jest.mock('../lib/resolveGitRepo')
 
 import lintStaged from '../lib/index'

test/integration.test.js

@@ -7,6 +7,16 @@ import normalize from 'normalize-path'
 
 jest.unmock('lilconfig')
 jest.unmock('execa')
+jest.mock('../lib/resolveConfig', () => ({
+  /** Unfortunately necessary due to non-ESM tests. */
+  resolveConfig: (configPath) => {
+    try {
+      return require.resolve(configPath)
+    } catch {
+      return configPath
+    }
+  },
+}))
 
 import { execGit as execGitBase } from '../lib/execGit'
 import lintStaged from '../lib/index'

test/loadConfig.spec.js

@@ -1,3 +1,14 @@
+jest.mock('../lib/resolveConfig', () => ({
+  /** Unfortunately necessary due to non-ESM tests. */
+  resolveConfig: (configPath) => {
+    try {
+      return require.resolve(configPath)
+    } catch {
+      return configPath
+    }
+  },
+}))
+
 import { dynamicImport } from '../lib/loadConfig.js'
 
 describe('dynamicImport', () => {