RFC: use clap::Command interface instead of procedure macro

[Roger-luo]

currently juliaup is implemented using the procedure macro, which is much simpler than clap::Command interface, however, this is much less flexible and less modular on creating more complicated CLI applications that contain multiple sub-commands.

For example, cargo uses a much modular structure based on the Command object interface https://github.com/rust-lang/cargo/blob/master/src/bin/cargo/commands/add.rs#L17

On the other hand, although errors in juliaup are handled, but not as exported as different terminal exit codes. This is something can be automatically enabled by a cargo-like CLI project structure.

More specifically, AFAIK there is no way to generate shell completions from procedure macro directly at the moment. The clap_completions crate is based on the ValueHint enum, but there is no way to define ValueHint in the derive macro. https://docs.rs/clap/latest/clap/_derive/index.html

And I can refactor juliaup into clap::Command to eat my own dog food, but just want to know if people want this.

[davidanthoff]

Hm, so far the simple story that we are using right now has worked well, I haven't really had a situation where I ran into a limitation around it? I am not generally against this, but at the moment I have limited bandwidth to review/do things here, and I think sorting out the remaining issues that are preventing us from making this the default Julia installer is probably a higher priority...

[Roger-luo]

I haven't really had a situation where I ran into a limitation around it? I am not generally against this, but at the moment I have limited bandwidth to review/do things here, and I think sorting out the remaining issues that are preventing us from making this the default Julia installer is probably a higher priority...

That's fully understandable, I think the main missing piece here is I want to have some shell completions but this is definitely not as urgent as other things. Just let me know if in the future you have time to review such a refactor - I don't think it's hard to do tho, just copy-pasting some code from cargo and re-organize the files.

[uncomfyhalomacro]

I will be willing to contribute to this once the remaining issues are fixed.

[sanmai-NL]

Using procedural macros complicates usage of RUSTFLAGS="-Ctarget-feature=+crt-static".
rust-lang/rust#71651

[fingolfin]

PR #753 adds support for shell completions without switching away from the clap "derive" interface to the more complicated "builder" interface (i.e. using clap::Command).

So assuming that PR is merged, I think this issue can be closed?

[Roger-luo]

it doesn't solve all the issues raised in this thread? but it's prob quite minor.

On the other hand, although errors in juliaup are handled, but not as exported as different terminal exit codes.