flow-webpack-plugin

A webpack plugin allowing to call [Flow][2] type checker during each webpack compilation.

![npm]()
![npm]()
![npm]()
![David]()

Key features

* It doesn't require flow to be in $PATH.
* No dependencies. Plugin can reuse project's flow-bin installation.
* It can make webpack to exit with non-zero return code, if flow validation fails.
* It works per project, not per file.

Installation

Run in you project directory:

``
npm install --save-dev flow-webpack-plugin flow-bin
`

or using yarn:

`
yarn add flow-webpack-plugin flow-bin --dev
`

Add to your webpack configuration file webpack.config.js:

`js
const FlowWebpackPlugin = require('flow-webpack-plugin')

module.exports = {
plugins: [
new FlowWebpackPlugin(),
// ...
],
// ...
}
`

Note: flow-bin package is not a hard dependency. If flow is already installed on your system,
it can be reused through flowPath option.

Screenshots

Valid codebase:
!Valid codebase

Flow validation error:
!Flow validation error

Configuration

Constructor of FlowWebpackPlugin accepts optional configuration object of following properties:

`js
const FlowWebpackPlugin = require('flow-webpack-plugin')

new FlowWebpackPlugin({
failOnError: false,
failOnErrorWatch: false,
reportingSeverity: 'error',
printFlowOutput: true,
flowPath: require.main.require('flow-bin'),
flowArgs: ['--color=always'],
verbose: false,
callback: (result) => {}
})
`

| option | type | default value | description |
| --- | --- | --- | --- |
| failOnError | boolean | false | Webpack exits with non-zero error code if flow typechecking fails. |
| failOnErrorWatch | boolean | false | Webpack in watch mode exits with non-zero error code if flow typechecking fails. |
| reportingSeverity | 'warning' | 'error' | 'error' | Webpack severity level of reported flow type problems. When using webpack-dev-server, page reload is blocked in case of webpack error. warning can be used to enable page reloads in case of flow errors when using webpack-dev-server. |
| printFlowOutput | boolean | true | true ~ Output of flow is printed at the end of webpack compilation in case of error, false ~ output of flow is discarded. |
| flowPath | string | require('flow-bin') if flow-bin package is installed. Otherwise the parameter is required. | Path to flow executable. It may be both absolute, relative to the 'cwd' of webpack process or just name of an executable on the PATH.
| flowArgs | Array | ['--color=always'] if standard output is directed to a terminal, otherwise [] | Flow command line arguments. See [flow cli documentation][1]. |
| verbose | boolean | false | It enables plugin logging for debug purposes. |
| callback | ({exitCode: number, stdout: string, stderr: string}) => ?Promise | (result) => {}` | Custom user function that is called when Flow check finishes and is passed Flow type check result. If function returns a promise, it is called asynchronously. |

Type annotations strip

This plugin performs type validation of the code. To remove the Flow type annotations and
create pure Javascript code [babel-plugin-transform-flow-strip-types][3] can be used.

[1]: https://flowtype.org/docs/cli.html
[2]: https://flowtype.org
[3]: https://www.npmjs.com/package/babel-plugin-transform-flow-strip-types