gatsby-plugin-mdx: jsxFrag should be set with latest version of @babel-plugin-transform-react-jsx

[loganmccaul]

Description

I'm getting the following error when compiling mdx files that contain a React fragment, <></> on a Gatsby site.

transform-react-jsx: pragma has been set but pragmaFrag has not been set

The issue is because MDX specifies /* @jsx mdx */ as the pragma, but never specifies a pragmaFrag which is now a requirement with babel-plugin-transform-react-jsx@7.9.x`

See the note here:
https://babeljs.io/docs/en/next/babel-plugin-transform-react-jsx.html#customizing-with-the-classic-runtime

Steps to reproduce

Unfortunately the code is private so I can't provide it as an example, but let me know if you want me to recreate in a public repo.

Expected behaviour

gatsby-plugin-mdx should set a jsxFrag value when specifying a custom jsx pragma.

So for example, every time /* @jsx mdx */ is set /* @jsxFrag ... */ should also be set.

Alternatively, babel-plugin-transform-react-jsx should use the default React.Fragment if none is specified.

I'm going to open an issue to babel-plugin-transform-react-jsx for default behavior and to mdx-js to add the same as well.

Related issues:

• babel-plugin-transform-react-jsx: babel-plugin-transform-react-jsx should use the default pragmaFrag if one isn't specified babel/babel#11321
• mdx-js issue: jsxFrag should be set with latest version of @babel-plugin-transform-react-jsx mdx-js/mdx#990

Let me know if there's a fragment pragma that makes sense and I'd be happy to do a PR.

Actual behaviour

babel-plugin-transform-react-jsx throws an error.

[loganmccaul]

Based on babel/babel#11321 (comment) it seems like up until babel/babel@748897b#diff-8c3c9c6362e23bd456da3fb129f49a57L10 mdx-js has been relying on React.Fragment being passed in from preset-react. Since that has now been removed, I think a fix would be to add

/* @jsxFrag React.Fragment */

Anywhere where /* @jsx mdx */ is specified.

Let me know if that makes sense and I'd be happy to do a PR.

[nicolo-ribaudo]

Note: we are restoring the old behavior of not throwing when using the preset, but I recommend enabling the fragment option since we'll re-introduce the error in Babel 8.

[existentialism]

We released a fix in 7.9.4 🎉!

[github-actions]

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[github-actions]

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[stephank]

This issue is old, but I'm just now seeing these exact errors in our build. Specifically:

EDIT: Just now realized the error message is slightly different. Sorry for the noise of this is a separate issue.

$ gatsby build --prefix-paths
success open and validate gatsby-configs - 0.053s
success load plugins - 0.461s
success onPreInit - 0.027s
success delete html and css files from previous builds - 0.004s
success initialize cache - 0.008s
success copy gatsby files - 0.048s
success onPreBootstrap - 0.023s
success createSchemaCustomization - 0.008s
success Checking for changed pages - 0.003s
success source and transform nodes - 1.549s
success building schema - 0.232s
info Total nodes: 144, SitePage nodes: 1 (use --verbose for breakdown)
success createPages - 0.006s
success Checking for changed pages - 0.002s
success createPagesStatefully - 1.020s
success update schema - 0.024s
success onPreExtractQueries - 0.001s
success extract queries from components - 0.303s
success write out redirect data - 0.010s
success onPostBootstrap - 0.003s
info bootstrap finished - 7.347s
success run static queries - 1.761s - 1/1 0.57/s
success run page queries - 0.167s - 56/56 335.02/s
success write out requires - 0.006s
failed Building production JavaScript and CSS bundles - 19.851s

 ERROR #98123  WEBPACK

Generating JavaScript bundles failed

[...]/src/pages/index.mdx: pragma and pragmaFrag cannot be set when runtime is automatic.
> 1 | import * as React from 'react'
    | ^
  2 |   /* @jsx mdx */
  3 | import { mdx } from '@mdx-js/react';
  4 | /* @jsx mdx */

File: src/pages/index.mdx

[...lots more follow...]

Curiously, I can fix this for us by setting a Yarn resolution for @babel/plugin-transform-react-jsx all the way back to 7.8.3. None of the newer releases on npm appear to work.

[nicolo-ribaudo]

It's because you (or gatsby) is using the runtime: "automatic" option of the JSX transform, which wasn't supported in 7.8.3 so it doesn't have any effect.