build_runner

fast_dev includes the builder. Same output as dart run fast_dev gen. Directory still comes from generate.output.

CLI-only projects can skip build_runner. If the project already uses build_runner, adding fast_dev is enough.

Install

dev_dependencies:
  fast_dev: ^0.0.1-beta.1
  build_runner: ^2.7.2

If the project already uses build_runner, add fast_dev next to the existing dev_dependencies. Do not add a second build_runner.

Commands

One command runs every enabled builder in the package. Asset codegen and other codegen come out together. You do not watch them separately.

# once
dart run build_runner build

# keep running — dart, assets, or config changes rebuild
dart run build_runner watch

Assets only, no build_runner:

dart run fast_dev gen

Rebuild one kind of output (unusual; daily watch does not need this):

# only rebuild outputs under lib/
dart run build_runner build --build-filter="lib/**"

# the same filter on watch skips assets/ and the config file
dart run build_runner watch --build-filter="lib/**"

Do not start two watch processes. One terminal, one command.

To keep other builders and skip Fast Dev:

targets:
  $default:
    builders:
      fast_dev:fast_dev:
        enabled: false

With other builders

Same as any other build_runner package: list it in dev_dependencies, share this command.

dart run build_runner watch

Edits under lib/ rebuild those generators. New images or a change to fast_dev_config.yaml rebuild assets.gen.dart. No extra process for Fast Dev.

Watch and assets

The default source set already includes lib/**, so other builders' .dart files are watched. assets/ and fast_dev_config.yaml are not. To rebuild when those change, add them in the app build.yaml and keep lib/**:

targets:
  $default:
    sources:
      include:
        - $package$
        - lib/**
        - test/**
        - pubspec.yaml
        - fast_dev_config.yaml
        - assets/**

Do not drop lib/**, or other builders stop watching.

Override output

Prefer generate.output in the config file. To change it only for build_runner:

targets:
  $default:
    builders:
      fast_dev:fast_dev:
        options:
          output: lib/generated/

How files land

The builder writes a cache manifest (.fast_dev.manifest.json). Post-process writes the sources. Stale files are removed via .dart_tool/fast_dev/owned_outputs.json. Paths outside the package are rejected.