# The MetaMask Build System

> _tl;dr_ `yarn dist` for prod, `yarn start` for local development.
> Add `--build-type flask` to build Flask, our canary distribution with more experimental features.

This directory contains the MetaMask build system, which is used to build the MetaMask Extension such that it can be used in a supported browser.
From the repository root, the build system entry file is located at [`./development/build/index.js`](https://github.com/MetaMask/metamask-extension/blob/develop/development/build/index.js).

Several package scripts invoke the build system.
For example, `yarn start` creates a watched development build, and `yarn dist` creates a production build.
Some of these scripts applies `lavamoat` to the build system, and some do not.
For local development, building without `lavamoat` is faster and therefore preferable.

The build system is not a full-featured CLI, but rather a script that expects some command line arguments and environment variables.
For instructions regarding environment variables, see [the main repository readme](../../README.md#building-locally).

Generally speaking, the build system consists of [`gulp`](https://npmjs.com/package/gulp) tasks that either manipulate static assets or bundle source files using [Browserify](https://browserify.org/).
Production-ready zip files are written to the `./builds` directory, while "unpacked" extension builds
are written to the `./dist` directory.

Our JavaScript source files are transformed using [Babel](https://babeljs.io/), specifically using
the [`babelify`](https://npmjs.com/package/babelify) Browserify transform.
Source file bundling tasks are implemented in the [`./development/build/scripts.js`](https://github.com/MetaMask/metamask-extension/blob/develop/development/build/scripts.js).

> Locally implemented Browserify transforms, _some of which affect how we write JavaScript_, are listed and documented [here](./transforms/README.md).

## Usage

```text
Usage: yarn build <entry-task> [options]

Commands:
  yarn build prod       Create an optimized build for production environments.

  yarn build dev        Create an unoptimized, live-reloaded build for local
                        development.

  yarn build test       Create an optimized build for running e2e tests.

  yarn build testDev    Create an unoptimized, live-reloaded build for running
                        e2e tests.

Options:
  --build-type        The "type" of build to create. One of: "beta", "flask",
                      "main"
                                                      [string] [default: "main"]
  --lint-fence-files  Whether files with code fences should be linted after
                      fences have been removed by the code fencing transform.
                      The build will fail if linting fails.
                      Defaults to `false` if the entry task is `dev` or
                      `testDev`, and `true` otherwise.
                                                   [boolean] [default: <varies>]
  --lockdown          Whether to include SES lockdown files in the extension
                      bundle. Setting this to `false` is useful e.g. when
                      linking dependencies that are incompatible with lockdown.
                                                       [boolean] [default: true]
  --policy-only       Stops the build after generating the LavaMoat policy,
                      skipping any writes to disk.
                                                       [boolean] [deafult: false]
  --skip-stats        Whether to refrain from logging build progress. Mostly
                      used internally.
                                                      [boolean] [default: false]
```