Add support for ESM config files

ESM config files can use `export default` to expose their configuration.
This commit also adds support for `.cjs` and `.mjs` config files.

Essentially 1091e32 but for config files.

Closes GH-50.

Author: wooorm

doc/configure.md

@@ -13,8 +13,9 @@ regardless of `detectConfig` and `rcName`.
 Otherwise, configuration files are detected if [`detectConfig`][detect-config]
 is turned on, depending on the following options:
 
-*   If [`rcName`][rc-name] is given, `$rcName` (JSON), `$rcName.js` (CommonJS),
-    `$rcName.yml` (YAML), and `$rcName.yaml` (YAML) are loaded
+*   If [`rcName`][rc-name] is given, `$rcName` (JSON), `$rcName.js` (CommonJS or
+    ESM), `$rcName.cjs` (CommonJS), `$rcName.mjs` (ESM), `$rcName.yml` (YAML),
+    and `$rcName.yaml` (YAML) are loaded
 *   If [`packageField`][package-field] is given, `package.json` (JSON) files
     are loaded and their `$packageField`s are used as configuration
 

doc/options.md

@@ -673,16 +673,23 @@ root[1] (1:1-2:1, 0-27)
 ## `options.rcName`
 
 Name of [configuration][configure] file to load.
-If given and [`detectConfig`][detect-config] is not `false`, `$rcName` files are
-loaded and parsed as JSON, `$rcName.js` are `require`d, and `$rcName.yml` and
-`$rcName.yaml` are loaded with `js-yaml` (`safeLoad`).
+If given and [`detectConfig`][detect-config] is not `false`, then:
+
+*   `$rcName` and `$rcName.json` are loaded and parsed as JSON
+*   `$rcName.yml` and `$rcName.yaml` are loaded with `js-yaml`
+*   `$rcName.js` are either `require`d or `import`ed
+*   `$rcName.cjs` are `require`d
+*   `$rcName.mjs` are `import`ed
+
+<!---->
 
 *   Type: `string`, optional
 
 ###### Example
 
-The following example processes `readme.md`, and allows configuration from
-`.remarkrc`, `.remarkrc.js`, and `.remarkrc.yaml` files.
+The following example processes `readme.md` and allows configuration from
+`.remarkrc`, `.remarkrc.yml`, `.remarkrc.yaml`, `.remarkrc.js`, `.remarkrc.cjs`,
+and `.remarkrc.mjs` files.
 
 ```js
 var engine = require('unified-engine')
@@ -775,7 +782,9 @@ File path to a config file to load, regardless of
 [`detectConfig`][detect-config] or [`rcName`][rc-name].
 
 If the file’s extension is `yml` or `yaml`, it’s loaded as YAML.
-If the file’s extension is `js`, it’s `require`d.
+If it’s `js`, it’s either `require`d or `import`ed.
+If it’s `cjs`, it’s `require`d.
+If it’s `mjs`, it’s `import`ed.
 If the file’s basename is `package.json`, the property at
 [`packageField`][package-field] is used.
 Otherwise, the file is parsed as JSON.

lib/configuration.js

@@ -1,7 +1,6 @@
 'use strict'
 
 var path = require('path')
-var Module = require('module')
 var yaml = require('js-yaml')
 var json = require('parse-json')
 var debug = require('debug')('unified-engine:configuration')
@@ -16,7 +15,9 @@ var own = {}.hasOwnProperty
 
 var loaders = {
   '.json': loadJson,
-  '.js': loadScript,
+  '.cjs': loadScriptOrModule,
+  '.mjs': loadScriptOrModule,
+  '.js': loadScriptOrModule,
   '.yaml': loadYaml,
   '.yml': loadYaml
 }
@@ -85,7 +86,11 @@ async function create(buf, filePath) {
   var fn = (filePath && loaders[path.extname(filePath)]) || defaultLoader
   var options = {prefix: self.pluginPrefix, cwd: self.cwd}
   var result = {settings: {}, plugins: []}
-  var contents = buf ? fn.apply(self, arguments) : undefined
+  var contents
+
+  if (filePath) {
+    contents = await fn.apply(self, arguments)
+  }
 
   if (self.configTransform && contents !== undefined) {
     contents = self.configTransform(contents, filePath)
@@ -121,20 +126,8 @@ async function create(buf, filePath) {
   return result
 }
 
-// Basically `Module.prototype.load`, but for a buffer instead of a file path.
-function loadScript(buf, filePath) {
-  var submodule = Module._cache[filePath]
-
-  if (!submodule) {
-    submodule = new Module(filePath, module)
-    submodule.filename = filePath
-    submodule.paths = Module._nodeModulePaths(path.dirname(filePath))
-    submodule._compile(String(buf), filePath)
-    submodule.loaded = true
-    Module._cache[filePath] = submodule
-  }
-
-  return submodule.exports
+function loadScriptOrModule(_, filePath) {
+  return loadFromAbsolutePath(filePath, this.cwd)
 }
 
 function loadYaml(buf, filePath) {
@@ -213,37 +206,10 @@ async function merge(target, raw, options) {
 
   async function addModule(id, value) {
     var fp = loadPlugin.resolve(id, {cwd: options.root, prefix: options.prefix})
-    var ext
     var result
 
     if (fp) {
-      ext = path.extname(fp)
-
-      /* istanbul ignore next - To do next major: Tests don’t run on Node 10 */
-      if (ext !== '.mjs') {
-        try {
-          result = require(fp)
-        } catch (error) {
-          if (ext !== '.cjs' && error.code === 'ERR_REQUIRE_ESM') {
-            ext = '.mjs'
-          } else {
-            throw fault(
-              'Cannot parse script `%s`\n%s',
-              path.relative(options.root, fp),
-              error.stack
-            )
-          }
-        }
-
-        if (result && typeof result === 'object' && result.__esModule) {
-          result = result.default
-        }
-      }
-
-      /* istanbul ignore next - To do next major: Tests don’t run on Node 10 */
-      if (ext === '.mjs') {
-        result = (await import(fp)).default
-      }
+      result = await loadFromAbsolutePath(fp, options.root)
 
       try {
         if (typeof result === 'function') {
@@ -308,3 +274,36 @@ function failingModule(id, error) {
     throw error
   }
 }
+
+async function loadFromAbsolutePath(fp, base) {
+  var ext = path.extname(fp)
+  var result
+
+  /* istanbul ignore next - To do next major: Tests don’t run on Node 10 */
+  if (ext !== '.mjs') {
+    try {
+      result = require(fp)
+    } catch (error) {
+      if (ext !== '.cjs' && error.code === 'ERR_REQUIRE_ESM') {
+        ext = '.mjs'
+      } else {
+        throw fault(
+          'Cannot parse script `%s`\n%s',
+          path.relative(base, fp),
+          error.stack
+        )
+      }
+    }
+
+    if (result && typeof result === 'object' && result.__esModule) {
+      result = result.default
+    }
+  }
+
+  /* istanbul ignore next - To do next major: Tests don’t run on Node 10 */
+  if (ext === '.mjs') {
+    result = (await import(fp)).default
+  }
+
+  return result
+}

test/configuration.js

@@ -11,7 +11,7 @@ var join = path.join
 var fixtures = join(__dirname, 'fixtures')
 
 test('configuration', function (t) {
-  t.plan(13)
+  t.plan(14)
 
   t.test('should fail fatally when custom rc files are missing', function (t) {
     var stderr = spy()
@@ -101,15 +101,15 @@ test('configuration', function (t) {
     }
   })
 
-  t.test('should support `.rc.js` modules (1)', function (t) {
+  t.test('should support `.rc.js` scripts (1)', function (t) {
     var stderr = spy()
 
     t.plan(1)
 
     engine(
       {
         processor: noop,
-        cwd: join(fixtures, 'malformed-rc-module'),
+        cwd: join(fixtures, 'malformed-rc-script'),
         streamError: stderr.stream,
         files: ['.'],
         rcName: '.foorc',
@@ -130,15 +130,15 @@ test('configuration', function (t) {
     }
   })
 
-  t.test('should support `.rc.js` modules (2)', function (t) {
+  t.test('should support `.rc.js` scripts (2)', function (t) {
     var stderr = spy()
 
     t.plan(1)
 
     engine(
       {
         processor: noop,
-        cwd: join(fixtures, 'rc-module'),
+        cwd: join(fixtures, 'rc-script'),
         streamError: stderr.stream,
         files: ['.'],
         rcName: '.foorc',
@@ -151,22 +151,46 @@ test('configuration', function (t) {
       t.deepEqual(
         [error, code, stderr()],
         [null, 0, 'one.txt: no issues found\n'],
-        'should support valid .rc modules'
+        'should support valid .rc scripts'
       )
     }
   })
 
-  t.test('should support `.rc.js` modules (3)', function (t) {
+  t.test('should support `.rc.js` scripts (3)', function (t) {
     var stderr = spy()
 
     t.plan(1)
 
-    require('./fixtures/rc-module/.foorc.js') // eslint-disable-line import/no-unassigned-import
+    engine(
+      {
+        processor: noop,
+        cwd: join(fixtures, 'rc-script'),
+        streamError: stderr.stream,
+        files: ['.'],
+        rcName: '.foorc',
+        extensions: ['txt']
+      },
+      onrun
+    )
+
+    function onrun(error, code) {
+      t.deepEqual(
+        [error, code, stderr()],
+        [null, 0, 'one.txt: no issues found\n'],
+        'should use Node’s module caching (coverage)'
+      )
+    }
+  })
+
+  t.test('should support `.rc.mjs` module', function (t) {
+    var stderr = spy()
+
+    t.plan(1)
 
     engine(
       {
         processor: noop,
-        cwd: join(fixtures, 'rc-module'),
+        cwd: join(fixtures, 'rc-module-mjs'),
         streamError: stderr.stream,
         files: ['.'],
         rcName: '.foorc',
@@ -184,7 +208,7 @@ test('configuration', function (t) {
     }
   })
 
-  t.test('should support `.rc.yaml` modules', function (t) {
+  t.test('should support `.rc.yaml` cpmfog files', function (t) {
     var stderr = spy()
 
     t.plan(1)
@@ -345,7 +369,7 @@ test('configuration', function (t) {
     engine(
       {
         processor: noop,
-        cwd: join(fixtures, 'malformed-rc-module'),
+        cwd: join(fixtures, 'malformed-rc-script'),
         streamError: stderr.stream,
         files: ['.'],
         extensions: ['txt'],

test/fixtures/malformed-rc-module/.foorc.js renamed to test/fixtures/malformed-rc-script/.foorc.js

@@ -0,0 +1,5 @@
+const config = {
+  settings: []
+}
+
+export default config