Plugins

[seaneagan]

Consider a similar approach to: https://github.com/chriso/cli#plugins

Existing issues for plugin-like functionality:

• Logging Logger injection #1
• Version Add Command.version which adds a --version flag #21
• Completion Tab completion #7

Help could be implemented internally as a plugin which is always included.

@Command(plugins: const [const Version(), const Completion(), const Logging()]
class MyCommand {
  static logger
}

The plugin API could initially be private, and there could just be hardcoded checks for known plugins. Presumably exposing the plugin API would be dependent on exposing the currently private Usage and CommandInvocation APIs, which is #19. Something like:

class Plugin {
  void updateUsage(Usage usage);
  bool onParse(CommandInvocation commandInvocation);
  bool onValidate(CommandInvocation commandInvocation);
}