ES Modules for the configuration file

CHANGELOG.md

@@ -2,6 +2,11 @@
 
 ## [Unreleased]
 
+### Added
+
+- ES Modules support for the configuration file ([#534](https://github.com/marp-team/marp-cli/pull/534))
+- `Config` type definition ([#534](https://github.com/marp-team/marp-cli/pull/534))
+
 ### Changed
 
 - Upgrade dependent packages to the latest versions ([#533](https://github.com/marp-team/marp-cli/pull/533))

README.md

@@ -455,7 +455,7 @@ export default async (constructorOptions) => {
 }
 ```
 
-> :information_source: Currently ESM engine can resolve only when using Marp CLI via Node.js. [The standalone binary](#standalone-binary) cannot resolve ESM due to [vercel/pkg#1291](https://github.com/vercel/pkg/issues/1291).
+> :information_source: Currently ES Modules can resolve only when using Marp CLI via Node.js. [The standalone binary](#standalone-binary) cannot resolve ESM due to [vercel/pkg#1291](https://github.com/vercel/pkg/issues/1291).
 
 #### `marp` getter property
 
@@ -512,7 +512,9 @@ $ npx marp --version
 
 ## Configuration file
 
-Marp CLI can be configured options with file, such as `marp.config.js`, `marp.config.cjs`, `.marprc` (JSON / YAML), and `marp` section of `package.json`. It is useful to configure settings for the whole of project.
+Marp CLI can be configured options with file, such as `marp.config.js`, `marp.config.mjs` (ES Modules), `marp.config.cjs` (CommonJS), `.marprc` (JSON / YAML), and `marp` section of `package.json`.
+
+It is useful to configure settings for the whole of project.
 
 ```javascript
 // package.json
@@ -536,10 +538,10 @@ pdf: true
 ```
 
 ```javascript
-// marp.config.js
-const markdownItContainer = require('markdown-it-container')
+// marp.config.mjs
+import markdownItContainer from 'markdown-it-container'
 
-module.exports = {
+export default {
   // Customize engine on configuration file directly
   engine: ({ marp }) => marp.use(markdownItContainer, 'custom'),
 }
@@ -549,6 +551,8 @@ By default we use configuration file that is placed on current directory, but yo
 
 If you want to prevent looking up a configuration file, you can pass `--no-config-file` (`--no-config`) option.
 
+> :information_source: Currently ES Modules can resolve only when using Marp CLI via Node.js. [The standalone binary](#standalone-binary) cannot resolve ESM due to [vercel/pkg#1291](https://github.com/vercel/pkg/issues/1291).
+
 ### Options
 
 | Key               |            Type             |        CLI option         | Description                                                                                                 |
@@ -578,6 +582,7 @@ If you want to prevent looking up a configuration file, you can pass `--no-confi
 | `pdfOutlines`     |      boolean \| object      |     `--pdf-outlines`      | Add outlines (bookmarks) to PDF                                                                             |
 | ┗ `pages`         |           boolean           |  `--pdf-outlines.pages`   | Make PDF outlines from slide pages (`true` by default when `pdfOutlines` is enabled)                        |
 | ┗ `headings`      |           boolean           | `--pdf-outlines.headings` | Make PDF outlines from Markdown headings (`true` by default when `pdfOutlines` is enabled)                  |
+| `pptx`            |           boolean           |         `--pptx`          | Convert slide deck into PowerPoint document                                                                 |
 | `preview`         |           boolean           |     `--preview` `-p`      | Open preview window                                                                                         |
 | `server`          |           boolean           |      `--server` `-s`      | Enable server mode                                                                                          |
 | `template`        |     `bare` \| `bespoke`     |       `--template`        | Choose template (`bespoke` by default)                                                                      |
@@ -589,20 +594,12 @@ If you want to prevent looking up a configuration file, you can pass `--no-confi
 
 [the whitelist object]: https://github.com/marp-team/marp-core#html-boolean--object
 
-### Advanced
-
-The advanced options that cannot specify through CLI options can be configured by file.
-
-#### Base options for engine constructor
+Some of options that cannot specify through CLI options can be configured by file.
 
-`options` can set the base options for the constructor of the used engine. You can fine-tune constructor options for [Marp Core](https://github.com/marp-team/marp-core#constructor-options) / [Marpit](https://marpit-api.marp.app/marpit).
+For example, `options` field can set the base options for the constructor of the used engine. You can fine-tune constructor options for the engine, [Marp Core](https://github.com/marp-team/marp-core#constructor-options) / [Marpit](https://marpit-api.marp.app/marpit).
 
-##### Example
-
-The below configuration will set constructor option for Marp Core as specified:
-
-- Disables [Marp Core's line breaks conversion](https://github.com/marp-team/marp-core#marp-markdown) (`\n` to `<br />`) to match for CommonMark, by passing [markdown-it's `breaks` option](https://markdown-it.github.io/markdown-it/#MarkdownIt.new) as `false`.
-- Disable minification for rendered theme CSS to make debug your style easily, by passing [`minifyCSS`](https://github.com/marp-team/marp-core#minifycss-boolean) as `false`.
+<details>
+<summary>Example: Customize engine's constructor option</summary>
 
 ```json
 {
@@ -615,8 +612,44 @@ The below configuration will set constructor option for Marp Core as specified:
 }
 ```
 
+This configuration will set the constructor option for Marp Core as specified:
+
+- Disables [Marp Core's line breaks conversion](https://github.com/marp-team/marp-core#marp-markdown) (`\n` to `<br />`) to match for CommonMark, by passing [markdown-it's `breaks` option](https://markdown-it.github.io/markdown-it/#MarkdownIt.new) as `false`.
+- Disable minification for rendered theme CSS to make debug your style easily, by passing [`minifyCSS`](https://github.com/marp-team/marp-core#minifycss-boolean) as `false`.
+
 > :warning: Some options may be overridden by used template.
 
+</details>
+
+### Type annotation
+
+For getting better IDE support (such as [IntelliSense](https://code.visualstudio.com/docs/editor/intellisense)) to write a config, you can annotate the config object through JSDoc, with Marp CLI's `Config` type.
+
+```javascript
+/** @type {import('@marp-team/marp-cli').Config} */
+const config = {
+  // ...
+}
+
+export default config
+```
+
+#### `Config` type with custom engine
+
+If you've swapped the engine into another Marpit based engine, you also can provide better suggestion for `options` field by passing the engine type to generics.
+
+```javascript
+/** @type {import('@marp-team/marp-cli').Config<typeof import('@marp-team/marpit').Marpit>} */
+const config = {
+  engine: '@marp-team/marpit',
+  options: {
+    // Suggest only Marpit constructor options, not Marp Core
+  },
+}
+
+export default config
+```
+
 ## API _(EXPERIMENTAL)_
 
 You can use Marp CLI through Node.js [if installed Marp CLI into your local project](#local-installation).

jest.config.js

@@ -32,7 +32,11 @@ module.exports = {
     '\\.s?css$': '<rootDir>/test/_transformers/css.js',
     '\\.png$': '<rootDir>/test/_transformers/png.js',
     '\\.pug$': '<rootDir>/test/_transformers/pug.js',
+
+    // TODO: Remove if Jest did not fail on ESM dynamic imports
     'custom-engine\\.mjs$': 'babel-jest',
+    'config\\.mjs$': 'babel-jest',
+    'esm-project/marp\\.config\\.js$': 'babel-jest',
   },
   transformIgnorePatterns: [`/node_modules/(?!${esModules.join('|')})`],
   testEnvironment: 'node',

package.json

@@ -154,7 +154,7 @@
     "@marp-team/marp-core": "^3.7.0",
     "@marp-team/marpit": "^2.5.0",
     "chokidar": "^3.5.3",
-    "cosmiconfig": "~8.1.3",
+    "cosmiconfig": "^8.2.0",
     "is-wsl": "^2.2.0",
     "puppeteer-core": "20.8.0",
     "remove": "^0.1.5",

src/config.ts

@@ -2,9 +2,13 @@
 import fs from 'fs'
 import path from 'path'
 import chalk from 'chalk'
-import { cosmiconfig } from 'cosmiconfig'
+import {
+  cosmiconfig,
+  cosmiconfigSync,
+  Options as CosmiconfigOptions,
+} from 'cosmiconfig'
 import { osLocale } from 'os-locale'
-import { info, warn } from './cli'
+import { info, warn, error as cliError } from './cli'
 import { ConverterOption, ConvertType } from './converter'
 import { ResolvableEngine, ResolvedEngine } from './engine'
 import { keywordsAsArray } from './engine/meta-plugin'
@@ -70,7 +74,7 @@ export type IMarpCLIConfig = Overwrite<
       progress?: boolean
       transition?: boolean
     }
-    engine?: ResolvableEngine | ResolvableEngine[]
+    engine?: ResolvableEngine
     html?: ConverterOption['html']
     keywords?: string | string[]
     lang?: string
@@ -110,6 +114,10 @@ export class MarpCLIConfig {
     return conf
   }
 
+  static isESMAvailable() {
+    return ResolvedEngine.isESMAvailable()
+  }
+
   private constructor() {} // eslint-disable-line @typescript-eslint/no-empty-function
 
   async converterOption(): Promise<ConverterOption> {
@@ -211,7 +219,7 @@ export class MarpCLIConfig {
         this.conf.image
 
       if (image === 'png') return ConvertType.png
-      if (image === 'jpeg') return ConvertType.jpeg
+      if (image === 'jpg' || image === 'jpeg') return ConvertType.jpeg
 
       // Detect from filename
       const lowerOutput = (output || '').toLowerCase()
@@ -331,7 +339,9 @@ export class MarpCLIConfig {
   }
 
   private async loadConf(confPath?: string) {
-    const explorer = cosmiconfig(MarpCLIConfig.moduleName)
+    const explorer = MarpCLIConfig.isESMAvailable()
+      ? cosmiconfig(MarpCLIConfig.moduleName)
+      : cosmiconfigSync(MarpCLIConfig.moduleName)
 
     try {
       const ret = await (confPath === undefined
@@ -343,10 +353,21 @@ export class MarpCLIConfig {
         this.conf = ret.config
       }
     } catch (e: unknown) {
+      const isErr = isError(e)
+
+      if (isErr && e.code === 'ERR_REQUIRE_ESM') {
+        // Show reason why `require()` failed in the current context
+        if ('pkg' in process) {
+          cliError(
+            'A standalone binary version of Marp CLI is currently not supported resolving ESM. Please consider using CommonJS, or trying to use Marp CLI via Node.js.'
+          )
+        }
+      }
+
       error(
         [
           'Could not find or parse configuration file.',
-          isError(e) && e.name !== 'Error' && `(${e.name})`,
+          isErr && `(${e.name}: ${e.message.trimEnd()})`,
           confPath !== undefined && `[${confPath}]`,
         ]
           .filter((m) => m)

src/converter.ts

@@ -1,6 +1,6 @@
 /* eslint-disable @typescript-eslint/no-non-null-assertion */
 import { URL } from 'url'
-import type { MarpOptions } from '@marp-team/marp-core'
+import type { Marp, MarpOptions } from '@marp-team/marp-core'
 import { Marpit, Options as MarpitOptions } from '@marp-team/marpit'
 import chalk from 'chalk'
 import type { Browser, Page, HTTPRequest } from 'puppeteer-core'
@@ -503,7 +503,9 @@ export class Converter {
       })
 
       // Resolve functional engine
-      engine = await Promise.resolve(engine(opts))
+      engine = await Promise.resolve(
+        engine(opts as typeof opts & { readonly marp: Marp })
+      )
     }
 
     if (isClass(engine)) engine = new engine(opts)

src/engine.ts

@@ -8,15 +8,18 @@ import { resolve as importMetaResolve } from 'import-meta-resolve'
 import { pkgUp } from 'pkg-up'
 import { error, isError } from './error'
 
-type MarpitInstanceOrClass = Marpit | typeof Marpit
+type FunctionalEngine<T extends typeof Marpit = typeof Marpit> = (
+  constructorOptions: ConstructorParameters<T>[0] & { readonly marp: Marp }
+) => Marpit | typeof Marpit | Promise<Marpit | typeof Marpit>
 
-type FunctionEngine = (
-  opts?: Marpit.Options
-) => MarpitInstanceOrClass | Promise<MarpitInstanceOrClass>
+export type Engine<T extends typeof Marpit = typeof Marpit> =
+  | Marpit
+  | typeof Marpit
+  | FunctionalEngine<T>
 
-export type Engine = MarpitInstanceOrClass | FunctionEngine
-
-export type ResolvableEngine = Engine | string
+export type ResolvableEngine<T extends typeof Marpit = typeof Marpit> =
+  | Engine<T>
+  | string
 
 const preResolveAsyncSymbol = Symbol('preResolveAsync')
 
@@ -188,7 +191,7 @@ export class ResolvedEngine<T extends Engine = Engine> {
         // Show reason why `require()` failed in the current context
         if ('pkg' in process) {
           error(
-            'A standalone binary version of Marp CLI is currently not supported resolving ESM engine. Please consider using CommonJS engine, or trying to use Marp CLI via Node.js.'
+            'A standalone binary version of Marp CLI is currently not supported resolving ESM. Please consider using CommonJS, or trying to use Marp CLI via Node.js.'
           )
         }
       }

src/index.ts

@@ -1,7 +1,35 @@
+import type { Marp } from '@marp-team/marp-core'
+import type { Marpit } from '@marp-team/marpit'
+import type { IMarpCLIConfig } from './config'
+import type { ResolvableEngine } from './engine'
+
 import { apiInterface } from './marp-cli'
 
+type Overwrite<T, U> = Omit<T, Extract<keyof T, keyof U>> & U
+
 export { ObservationHelper, waitForObservation } from './marp-cli'
 export { CLIError, CLIErrorCode } from './error'
 
 export const marpCli = apiInterface
 export default apiInterface
+
+// ---
+
+// eslint-disable-next-line @typescript-eslint/no-empty-interface -- Use interface instead of type for better IntelliSense
+export interface Config<Engine extends typeof Marpit = typeof Marp>
+  extends Overwrite<
+    Omit<
+      IMarpCLIConfig,
+      /**
+       * This option is internal setting for collaboration with Marp team tools such as Marp for VS Code.
+       * It is not designed for users because the result of conversion may break if set wrong base URL.
+       */
+      'baseUrl'
+    >,
+    {
+      engine?: ResolvableEngine<Engine>
+      image?: 'png' | 'jpeg'
+      images?: 'png' | 'jpeg'
+      options?: ConstructorParameters<Engine>[0]
+    }
+  > {}

test/__mocks__/cosmiconfig.ts

@@ -0,0 +1,25 @@
+const cosmiconfig: typeof import('cosmiconfig') =
+  jest.requireActual('cosmiconfig')
+
+const {
+  cosmiconfig: originalCosmiconfig,
+  defaultLoaders,
+  defaultLoadersSync,
+} = cosmiconfig
+
+// Because of v8's bug, Jest fails with SIGSEGV if used dynamic import.
+// When using ESM in tests, you have to set up Jest to transpile config files into CommonJS with Babel.
+cosmiconfig.cosmiconfig = jest.fn((moduleName, options) => {
+  return originalCosmiconfig(moduleName, {
+    loaders: {
+      // cosmiconfig sync loader is using `require()` to load JS
+      ...defaultLoaders,
+      '.js': defaultLoadersSync['.js'],
+      '.mjs': defaultLoadersSync['.js'],
+      '.cjs': defaultLoadersSync['.js'],
+    },
+    ...(options ?? {}),
+  })
+})
+
+module.exports = cosmiconfig

test/_configs/esm-project/marp.config.js

@@ -0,0 +1,6 @@
+/** @type {import('../../../src/index').Config} */
+const config = {}
+
+export default config
+
+console.debug('A config file within ESM project was loaded.')

test/_configs/esm-project/package.json

@@ -0,0 +1,4 @@
+{
+  "private": true,
+  "type": "module"
+}

test/_configs/mjs/config.mjs

@@ -0,0 +1,3 @@
+export default {}
+
+console.debug('A config file with .mjs extension was loaded.')