prettier-plugin-flatbuffers

If you use Prettier, this plugin gives you canonical FlatBuffers schema formatting with no extra commands. It's a thin shim over flatbuffers-format — same output, same guarantees, just Prettier-routed. Install it, add it to your .prettierrc, and .fbs files start formatting alongside everything else your editor already touches.

Install

npm i -D prettier prettier-plugin-flatbuffers flatbuffers-format

flatbuffers-format is a regular runtime dependency, so npm will pull it in for you — the third entry above is just for clarity in your package.json.

Activate

.prettierrc:

{
  "plugins": ["prettier-plugin-flatbuffers"]
}

That's it. Any .fbs file Prettier sees from then on is formatted by this plugin.

npx prettier --write 'src/**/*.fbs'

Editor integrations (VS Code, Neovim, etc.) pick up the plugin automatically as long as Prettier itself does.

Behavior

If a .flatbuffers-format.json applies to the file (the nearest one in its directory or any parent), the plugin uses it and ignores Prettier's options below, so Prettier formats exactly as the flatbuffers-format CLI and the other editor plugins do. See the config file docs.

Without one, the plugin maps Prettier's options to flatbuffers-format's FormatOptions:

| Prettier option | Effect | |----------------------------|---------------------------------------------------------------------------------| | tabWidth (default 2) | Forwarded as the engine's indent (count of indent characters per level). | | useTabs (default false)| One tab per indent level, as in Prettier; tabWidth then only sets how wide a tab looks in your editor. | | printWidth (default 80)| Forwarded as the engine's lineWidth. Drives the "does it fit on one line" decision for small enums/unions/single-field bodies and for line-comment wrapping. | | trailingComma (default "all") | "all" and "es5" put a comma after the last value of an expanded enum or union; "none" leaves it off. | | bracketSpacing (default true) | { A, B } or {A, B} for bodies on one line. | | objectWrap (default "preserve") | "preserve" keeps a body expanded when the source has a line break after its {; "collapse" puts every body that fits on one line. | | endOfLine | Handled by Prettier itself ("lf", "crlf", "cr", "auto"). The engine always emits \n; Prettier post-processes the output to the requested line ending. | | requirePragma, checkIgnorePragma, insertPragma | Work as in Prettier: the pragmas are @format / @prettier and @noformat / @noprettier in a comment at the top of the file. |

A .flatbuffers-format.json with requirePragma: true should not be combined with Prettier's insertPragma: true. Prettier inserts the pragma before the plugin can read the config file, so every file gets formatted. Set requirePragma in Prettier's own config instead, or drop insertPragma.

// prettier-ignore above a declaration keeps it as written. Other Prettier options (singleQuote, semi, …) are ignored, as .fbs has no syntax for them.

How it works

Prettier 3 plugins normally define a parse function that builds an AST and a print function that turns it back into a Doc tree. That's the right shape when the formatter is of Prettier, not just plugged into it. Here, the canonical form is defined entirely by flatbuffers-format, so we use Prettier's preprocess hook to run format() on the source. The text Prettier's printer receives is already canonical; the printer just returns it verbatim. No AST round-tripping, no risk of drift between the engine and a duplicated Prettier-side implementation.

For everything about the formatting rules themselves (idempotency guarantees, what's preserved, what's normalized, comment handling, the cookbook of before/after examples) see the flatbuffers-format README.

Development setup

Inside the monorepo, the flatbuffers-format dependency is wired to the sibling project via a relative file: install:

"dependencies": {
  "flatbuffers-format": "file:../flatbuffers-formatter"
}

That means the sibling must be built first:

cd flatbuffers-formatter && npm ci && npm run build
cd ../prettier-plugin-flatbuffers && npm ci && npm run build && npm test

When this plugin is published to npm, the file: reference will be swapped for a pinned ^0.1 range against the published flatbuffers-format package.

Releases

Releases are automated via release-please. Land a Conventional Commit on main → a release PR appears → merging it tags and publishes.

License

MIT. See LICENSE.