Consider Formatly instead of a direct Prettier dependency in @react-router/dev

[aleclarson]

Summary

Please consider using Formatly in @react-router/dev instead of depending directly on Prettier.

Motivation

packages/react-router-dev/cli/useJavascript.ts currently imports prettier and calls prettier.format(...) on JavaScript generated by Babel. As a result, @react-router/dev includes Prettier as a runtime dependency even when the consuming project uses another formatter such as Biome, dprint, or deno fmt.

Formatly is intended for developer tools that generate user-owned files. It detects and invokes the formatter already configured by the project, with support for Biome, deno fmt, dprint, and Prettier, with Oxfmt support pending in Formatly PR #544.

Possible approach

Consider replacing the direct Prettier integration with Formatly so generated JavaScript follows the consuming project's formatter configuration.

The current transpile function returns a formatted string, while Formatly operates on generated files or glob patterns. Integration may therefore involve formatting the generated JavaScript after it is written to disk, or adjusting the surrounding workflow as appropriate.

If no supported formatter is configured, React Router could retain the Babel output or otherwise preserve the current fallback behavior.

References

• Current call site:

  react-router/packages/react-router-dev/cli/useJavascript.ts

  Line 29 in 8bc59bc

  return await prettier.format(mjs.code, { parser: "babel" });

• Formatly: https://github.com/JoshuaKGoldberg/formatly

[brophdawg11]

I converted this to a discussion because it'a a feature request. I don't think this is necessary since it's only used in a single case (react-router reveal --no-typescript) and then the file is owned by the project and local formatting can be applied on the committed file and prettier never comes into the equation again. We have discussed removing the --no-typescript flag previously and honestly that was probably an oversight when we launched v8.

[aleclarson]

If removing the feature that relies on a prettier dependency altogether is a better path forward, I'm all for it. My goal is only to keep Prettier out of my lockfile, because it's confusing my agents for some odd reason.

[aleclarson]

Alternatively, the --no-typescript flag could be used by React Router's code generator, so it can control the initial output instead of triggering a post-processing step.

[brophdawg11]

yeah I think it would be better to drop the formatting aspect from the runtime deps entirely. I opened a PR to do this at build time so we can just copy the proper .jsx/.jsx file and move prettier to a dev dep #15373

[Sleeman01]

This is a great suggestion. Replacing direct runtime dependencies on Prettier in CLI scaffolding tools improves bundle weight and respects the user's preferred toolchain (e.g., Biome, dprint).

Here are a few technical considerations for integrating formatly into @react-router/dev:

1. In-Memory Formatting vs. Disk Formatting

As noted, useJavascript.ts currently formats code in-memory right after Babel transpilation (prettier.format(mjs.code, ...)).

Since formatly operates on files on disk rather than raw strings:

• Option A (Post-Write Step): Write the generated JavaScript files to disk first, then execute formatly on the written paths/globs.
• Option B (Fallback Handling): If formatly does not detect an existing project formatter (Biome, Deno, Prettier, dprint), preserve the unformatted Babel output or gracefully log a fallback warning rather than shipping a full Prettier bundle.

2. Dependency Footprint

Removing prettier from dependencies of @react-router/dev reduces the install footprint for projects using alternative formatters or zero-config builds.

3. Implementation Checklist

• Remove prettier from packages/react-router-dev/package.json dependencies.
• Update useJavascript.ts (or the downstream file-writing utility) to invoke formatly after file generation.
• Add unit/integration tests verifying that file generation succeeds with and without a detected formatter config.

Happy to open a PR for this if the maintainers are open to the change!