Add subcommand for generating shell completion scripts

[tranzystorekk]

Since clap gives those basically for free 😄

[lpil]

Very cool! How do we use it?

[tranzystorekk]

@lpil depends on shell, but basically for example gleam completion zsh > <completion_dir>/_gleam, usually package maintainers put them in global completion paths like /usr/share/bash-completion/completions/ or /usr/share/zsh/site-functions/ for Arch

[tranzystorekk]

A user typically configures a local completion directory and adds it to an env var like FPATH in zsh

[tranzystorekk]

Ugh, seems AppSettings::Hidden doesn't hide commands from the completion generator

[lpil]

Hmm, that is a bit annoying. It could be OK if we remove the print-config command.

Perhaps newer versions of clap might hide them? It seems odd they are not hidden. It would be frustrating in future if we wanted to hide something more substantial than print-config

[tranzystorekk]

Perhaps newer versions of clap might hide them?

Did a quick check on clap 3.0.0-beta.5 for my own project, hidden apps still show up in scripts 🙁

EDIT: The issue has been there for a while: clap-rs/clap#1335

[lpil]

It looks like it will be fixed in a future release? clap-rs/clap#2541

[tranzystorekk]

From the discussion it seems the status is back to clap-rs/clap#1335

[lpil]

Ah, that is a shame

[lpil]

I'm going to close this as we're a bit stuck, but please feel free to reopen once we can hide commands.