TypeError: `attacher.call` is not a function when using `remark-shiki-twoslash` with `unified`

[mattcroat]

Hey! 👋

I'm using remark-shiki-twoslash with unified and I get this error TypeError: attacher.call is not a function. I already opened a discussion at https://github.com/unifiedjs/unified/discussions/187 but I was told to raise the issue here.

Here is the reproduction on StackBlitz. I have a simple Express server without TypeScript and I use "type": "module" in package.json.

// index.js

import { unified } from 'unified'
import shikiTwoslash from 'remark-shiki-twoslash'
import parseMarkdown from 'remark-parse'
import serializeMarkdown from 'remark-stringify'
import markdownToHtml from 'remark-rehype'
import markdownToHtmlAgain from 'rehype-raw'
import serializeHtml from 'rehype-stringify'

const result = await unified()
  .use(parseMarkdown)
  .use(serializeMarkdown)
  .use([
    [shikiTwoslash, { theme: 'dark-plus' }]
    // ...
  ])
  .use(markdownToHtml, { allowDangerousHtml: true })
  .use(markdownToHtmlAgain)
  .use(serializeHtml)
  .process('```js \n console.log("Hello, World!") \n ```')

> server@ start /server
> node ./src/index.js

file:///server/node_modules/unified/lib/index.js:136
      const transformer = attacher.call(processor, ...options)
                                   ^

TypeError: attacher.call is not a function
    at Function.freeze (file:///server/node_modules/unified/lib/index.js:136:36)
    at Function.process (file:///server/node_modules/unified/lib/index.js:375:15)
    at output (file:///server/src/index.js:25:4)
    at file:///server/src/index.js:35:20
    at ModuleJob.run (node:internal/modules/esm/module_job:197:25)
    at async Promise.all (index 0)
    at async ESMLoader.import (node:internal/modules/esm/loader:337:24)
    at async loadESM (node:internal/process/esm_loader:88:5)
    at async handleMainPromise (node:internal/modules/run_main:61:12)

[orta]

Interesting, perhaps there's different constraints when running inside a module - I don't have any code which runs in ESM node, so I've not hit it. Open to PRs though 👍🏻

[chopfitzroy]

Heya @mattcroat

Can you try using:

.use([
    [shikiTwoslash.default, { theme: 'dark-plus' }]
    // ...
  ])

Have updated your example as well: https://stackblitz.com/edit/node-shiki-twoslash-tcez4v and it appears to be working as expected.

I ran into a similar issue using remark-shiki-twoslash with Astro.

[enpitsuLin]

@chopfitzroy ’s advice is useful

I Think remark-shiki-twoslash maybe should be a pure ESM library

[arcanis]

It occurs because you list the esm entrypoint through the module key, which Node doesn't actually use when resolving import calls (it only reads the exports field). As a result, the cjs version of the library is loaded and, while Node tries to shim it to look like an ESM module, it doesn't do it perfectly and messes up the translation, causing the default export to be unnecessarily wrapped.

To fix it, you have to list in the package.json something akin to:

{
  "main": "./dist/index.js",
  "module": "./dist/remark-shiki-twoslash.esm.mjs",
  "typings": "./dist/index.d.ts",
  "exports": {
    ".": {
      "import": "./dist/remark-shiki-twoslash.esm.mjs",
      "types": "./dist/index.d.ts",
      "default": "./dist/index.js"
    }
  }
}

Note that the esm file also needs to have its extension be .mjs, not .js - otherwise Node will complain and the import will fail. That's why I didn't submit a PR - this stuff seems to be handled by TSDX, and I don't know if it supports configuring that.

[Levent0z]

When I use the .default workaround, nextjs site builds, but all triple-tick blocks are removed from the resulting HTML and appear to be replaced with <!-- -->. This is my next.config.mjs:

const nextConfig = {
    reactStrictMode: true,
    webpack: (config, options) => {
        config.module.rules.push({
            test: /\.mdx?$/,
            use: [
                options.defaultLoaders.babel,
                {
                    loader: '@mdx-js/loader',
                    options: {
                        providerImportSource: '@mdx-js/react',
                        remarkPlugins: [
                            remarkFrontmatter,
                            [remarkShikiTwoslash.default, {
                                themes: ['dark-plus', 'light-plus'],
                                alwayRaiseForTwoslashExceptions: true,
                                // https://github.com/shikijs/twoslash/issues/131
                                disableImplicitReactImport: true,
                            }],
                            remarkGfm,
                            remarkMath,
                        ],
                        rehypePlugins: [
                            [rehypeKatex, { throwOnError: true, strict: true, output: 'mathml' }],
                            rehypeSlug,
                            [rehypeAutolinkHeadings, { behavior: 'wrap' }],
                            // [withShiki, { highlighter }],
                            [template, { template: wrapTemplate }]
                        ],
                    },
                },
            ],
        });
        // Fixes npm packages (mdx) that depend on `fs` module
        if (!options.isServer) {
            config.resolve.fallback.fs = false
        }
        return config;
    },
    pageExtensions: ['js', 'jsx', 'tsx', 'md', 'mdx'],
    images: {
        loader: 'imgix',
        path: 'https://images.unsplash.com/',
    },
};