build_runner

The build_runner package provides general-purpose commands for generating files, including testing the generated files or serving both source and generated files. This page explains how to use build_runner. To learn how to use build_runner with a specific package, see the documentation for that package.

The build_runner commands work with builders—packages that use the Dart build system to generate output files from input files. For example, the json_serializable and built_value_generator packages define builders that generate Dart code.

Although the Dart build system is a good alternative to reflection (which has performance issues) and macros (which Dart's compilers don't support), it can do more than just read and write Dart code. For example, the sass_builder package implements a builder that generates .css files from .scss and .sass files.

To use build_runner, add a dev dependency on build_runner to your app's pubspec:

dev_dependencies:
  # ···
  build_runner: ^2.7.0
  build_test: ^3.3.0

Depending on build_test is optional; do it if you'll be testing your code.

As usual after pubspec.yaml changes, run dart pub get or dart pub upgrade:

$ dart pub get

The following is an example of using the build_runner build command:

$ # From a directory that contains a pubspec.yaml file:
$ dart run build_runner build

The build_runner package includes the following commands:

build

Performs a one-time build.

serve

Runs a development server. Instead of directly using this command, you can use webdev serve, which has convenient default behavior.

test

Runs tests.

watch

Launches a build server that watches for edits to input files. Responds to changes by performing incremental rebuilds.

• webdev guide (use if you're working on web-specific code)
• build_runner guide
• packages with the build_runner dependency
• packages with the build dependency