Add shell auto-completion support for Bash, Fish and Zsh

[braph]

Hello,

I'm the author of crazy-complete and I've started working on a completion definition for legendary.

I know there are already two open issues about Bash completion, but the completions proposed there are not as fine-grained as mine.

You can find the definition file as well as pre-generated auto-completion files here inside the legendary directory.

Here's how you can try out the scripts:

• bash: source ./generated/bash/legendary
• fish: source ./generated/fish/legendary.fish
• zsh: source ./generated/zsh/legendary.sourceable

The definition file is still a work in progress and has some gaps: In a few places I wasn't always
sure what the completion should be (e.g. whether an option should complete to a file or directory).
These spots are marked with # TODO comments in the definition file.

Here are some details about the setup:

• The completion files are currently built via the Makefile.
  The following arguments are passed to crazy-complete:

  • --include-file=: Includes additional files into the generated output.
    These contain helper functions used by crazy-complete.
  • --inherit-options=True: Ensures that subcommands also inherit the options
    of their parent command.

• Some directives inside legendary.yaml worth clarifying:

  • final: true: Marks an option as final, meaning no more options may follow it.
  • groups: [...]: Defines mutually exclusive groups of options.
  • complete: ['exec', '<function>']: Executes function and uses its output for completing.
  • complete: ['combine', [...]]: Combines multiple completers into one.
  • complete: ['choices', [...]]: Complete from a fixed list of words.
  • complete: ['none']: Marks an option as taking an argument but without a completer.

Feedback and contributions, especially towards resolving the TODOs in the definition file, would be very welcome!