Configuration

Create fast_dev_config.yaml next to pubspec.yaml.

The tool can run without it and will use the defaults below. A file in the repo is better: class name, style, output, and variants are visible.

What Flutter packs into the app still comes from flutter.assets in pubspec.yaml. fast_dev_config.yaml does not change that. It only controls code generation (output dir, class name, style, variants).

Which keys each feature reads, and the rules for them: Assets. Theme and locale: Theme and locale.

How it loads

1. dart run fast_dev -c path/to.yaml gen — that file only. It has to exist. No fallback to defaults.
2. No -c — walk up to pubspec.yaml, then read fast_dev_config.yaml beside it.
3. Package root found, no config file — defaults, plus a warning.

A relative -c is resolved from the current working directory. Run the CLI from the package root. Keep -c for one-off experiments.

Merge

Defaults first. Keys you write override. Partial files are fine.

Lists replace, they do not append. Default theme.folders.light is [light]. If you write light: [day], the result is [day], not [light, day].

Unknown keys warn and are ignored. The run still succeeds. Reserved keys do the same: imports, generate.fonts, generate.colors warn and are not treated as implemented.

Write version: 1. Only 1 is accepted. Omit it and it is 1. Any other integer fails.

Check the merge

After editing YAML (writes nothing):

dart run fast_dev config

Prints the package root, the file that was read, warnings, and the merged values. Then dart run fast_dev gen.

build_runner can override the output dir with options.output in the app build.yaml. See build_runner.

Default config

Every key that is parsed today, with the built-in defaults. Drop what you do not need.

Field details live on the feature pages. Today that is Assets. Theme and locale keys: Theme and locale.

# Schema. Only 1 is accepted. Omit it and it is 1. Any other integer fails.
version: 1

# Code generation. assets is the only section under it today.
# Reserved keys fonts / colors warn and are ignored.
generate:
  # Where .gen.dart is written, relative to the package root.
  # Does not change what Flutter packs. Empty string fails.
  # Backslashes become /. A missing trailing slash is added.
  output: lib/gen/fast_dev/

  # Passed to dart_style. Must be > 0.
  # Match dart format / analysis_options.yaml.
  line_length: 80

  # Asset path generation. Turn it off and assets.gen.dart is not written.
  # Field details: Assets.
  assets:
    # false skips generation. Use real YAML booleans (true / false).
    enabled: true

    # Root class name. Must be a Dart identifier. Prefer PascalCase.
    class_name: Assets

    # How paths become members: nested | camel | snake
    style: nested

    # Theme and locale folders. Off by default: light/, dark/, zh/ stay
    # normal nested folders. Turn them on only when files are actually
    # split that way. Details: Assets.
    variants:
      theme:
        # When true, folders in folders.light / folders.dark are variants.
        enabled: false
        folders:
          # Light / dark folder names. A string or a list.
          # Lists replace, they do not append.
          light: [light]
          dark: [dark]
      locale:
        # When true, folders cannot be empty.
        enabled: false
        # Locale folders to strip. folders: zh also works.
        folders: []
        # Miss on the current locale:
        # file = the file with no locale folder; or a code in folders.
        fallback: file

How to write it

1. Create the file. Only write the keys you want to change.
2. Leave variants off if you do not split by theme or locale.
3. Turn theme on if you have dark/ or light/. Rename folders if your names differ.
4. Turn locale on if you have zh/ / en/, and list them in folders.
5. Run dart run fast_dev config.
6. Run dart run fast_dev gen.