From 8d3b176a7af75790efbcd1f63f73e7ef51f6b377 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Iiro=20J=C3=A4ppinen?= <iiro@jappinen.fi>
Date: Sun, 14 Nov 2021 09:30:46 +0200
Subject: [PATCH] feat: support loading `.mjs` config

---
 .eslintrc.json                |  5 ++++-
 README.md                     |  6 +++++-
 jest.config.js                |  1 +
 lib/index.js                  |  5 +++++
 test/__mocks__/esm-config.mjs |  3 +++
 test/index.spec.js            | 21 +++++++++++++++++++++
 6 files changed, 39 insertions(+), 2 deletions(-)
 create mode 100644 test/__mocks__/esm-config.mjs

diff --git a/.eslintrc.json b/.eslintrc.json
index 9b4f9aa7b..f04582226 100644
--- a/.eslintrc.json
+++ b/.eslintrc.json
@@ -33,7 +33,10 @@
     ],
     "no-console": "off",
     "node/no-unsupported-features/es-builtins": "error",
-    "node/no-unsupported-features/es-syntax": ["error", { "ignores": ["modules"] }],
+    "node/no-unsupported-features/es-syntax": [
+      "error",
+      { "ignores": ["dynamicImport", "modules"] }
+    ],
     "node/no-unsupported-features/node-builtins": "error",
     "prettier/prettier": "error"
   }
diff --git a/README.md b/README.md
index 9cca38044..d4452b61b 100644
--- a/README.md
+++ b/README.md
@@ -106,7 +106,11 @@ Starting with v3.1 you can now use different ways of configuring lint-staged:
   - `.lintstagedrc.json`
   - `.lintstagedrc.yaml`
   - `.lintstagedrc.yml`
-- `lint-staged.config.js`, `.lintstagedrc.js`, or `.lintstagedrc.cjs` file in JS format
+  - `.lintstagedrc.mjs`
+  - `.lintstagedrc.js`
+  - `.lintstagedrc.cjs`
+- `lint-staged.config.mjs` file in ESM format
+- `lint-staged.config.js`, `.lintstagedrc.js`, or `.lintstagedrc.cjs` file in CommonJS format
 - Pass a configuration file using the `--config` or `-c` flag
 
 See [cosmiconfig](https://github.com/davidtheclark/cosmiconfig) for more details on what formats are supported.
diff --git a/jest.config.js b/jest.config.js
index d05ef8a0a..b7568c554 100644
--- a/jest.config.js
+++ b/jest.config.js
@@ -7,6 +7,7 @@ const config = {
   testEnvironment: 'node',
   transform: {
     '\\.[jt]sx?$': 'babel-jest',
+    '\\.mjs$': 'babel-jest',
   },
   /** Also transform ESM packages in `node_modules` */
   transformIgnorePatterns: [],
diff --git a/lib/index.js b/lib/index.js
index 2241554d4..368d2ad80 100644
--- a/lib/index.js
+++ b/lib/index.js
@@ -32,11 +32,16 @@ const loadConfig = (configPath) => {
       '.lintstagedrc.json',
       '.lintstagedrc.yaml',
       '.lintstagedrc.yml',
+      '.lintstagedrc.mjs',
       '.lintstagedrc.js',
       '.lintstagedrc.cjs',
+      'lint-staged.config.mjs',
       'lint-staged.config.js',
       'lint-staged.config.cjs',
     ],
+    loaders: {
+      '.mjs': (path) => import(path).then((module) => module.default),
+    },
   })
 
   return configPath ? explorer.load(resolveConfig(configPath)) : explorer.search()
diff --git a/test/__mocks__/esm-config.mjs b/test/__mocks__/esm-config.mjs
new file mode 100644
index 000000000..df7963d08
--- /dev/null
+++ b/test/__mocks__/esm-config.mjs
@@ -0,0 +1,3 @@
+export default {
+  '*': 'mytask',
+}
diff --git a/test/index.spec.js b/test/index.spec.js
index f323826c4..12e1262dc 100644
--- a/test/index.spec.js
+++ b/test/index.spec.js
@@ -193,6 +193,27 @@ describe('lintStaged', () => {
     `)
   })
 
+  it('should read config from relative ESM file', async () => {
+    expect.assertions(1)
+
+    await lintStaged(
+      {
+        configPath: path.join('test', '__mocks__', 'esm-config.mjs'),
+        debug: true,
+        quiet: true,
+      },
+      logger
+    )
+
+    expect(logger.printHistory()).toMatchInlineSnapshot(`
+      "
+      LOG Running lint-staged with the following config:
+      LOG {
+        '*': 'mytask'
+      }"
+    `)
+  })
+
   it('should use config object', async () => {
     expect.assertions(1)