If you are writing a library using the Flow type system, you might want to make your library's types available to your end users. One way to do this is to place a file with a .js.flow extension alongside your bundled source code. Flow knows to look inside files like this for type information.

This Rollup plugin will create one of these .js.flow files alongside each of your output files. The .js.flow file will simply export * from your un-bundled input file, allowing Flow to find your original type information.

Here is an example rollup.config.js file using this plugin:

import flowEntry from 'rollup-plugin-flow-entry'

export default {
  input: './src/index.js',
  output: { file: './lib/index.js', format: 'cjs' },
  plugins: [
    flowEntry()
    // You will also need rollup-plugin-babel or rollup-plugin-flow
    // in here to strip your type annotations...
  ]
}

This will produce a file called lib/index.js.flow alongside the normal lib/index.js output file. The output file will look like this:

// @flow

export * from '../src/index.js'

If you want to enable stricter type checking, pass a mode into configuration options:

export default {
  input: './src/index.js',
  output: { file: './lib/index.js', format: 'cjs' },
  plugins: [
    flowEntry({
      mode: 'strict-local',
    })
  ]
}

If you use Rollup's built-in code splitting feature, this plugin will create one Flow entry point for each entry chunk.

This plugin can also detect when rollup-plugin-multi-entry is being used, and will create a single combined Flow entry point when appropriate.