Target tab completion invokes `rustup`

[mkoncek]

Problem

Invoking cargo build --target <TAB> invokes rustup. Some environments may not have it installed and I do not see why it should be invoked if the tab completion can run equivalent of rustc --print target-list.

Steps

1. Set up a basic Rust project with cargo
2. Write cargo build --target on terminal and then press the TAB key.
3. If rustup is not installed, terminal will print:
   cargo build --target bash: rustup: command not found

Possible Solution(s)

I suppose cargo could return the output of rustc --print target-list

Notes

It is generally a good idea to depend only on the most basic tools, especially if they get the job done right, like rustc does.

Version

cargo 1.71.0
release: 1.71.0
host: x86_64-unknown-linux-gnu
libgit2: 1.6.4 (sys:0.17.1 system)
libcurl: 8.0.1 (sys:0.4.61+curl-8.0.1 system ssl:OpenSSL/3.0.9)
os: Fedora 38.0.0 [64-bit]

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[epage]

Interesting, the zsh completions are using rustc --print target-list but the bash ones aren't.

zsh support for targets was added in #8740

bash support was added in #6640

I don't see any references to why different strategies were taken, so it seems like we could consolidate down to just rustc

[weihanglo]

Another idea is we can go with rustup way first and fall back to rustc --print target-list.

[epage]

Is there a reason to prefer rustup? I guess so you can check which targets are actually installed?

[weihanglo]

Yes. Completing with installed ones. rustc --print target-list now prints 218 target triples which doesn't sounds too friendly.

[epage]

Yeah, making both do rustup and then fallback seems like the ideal

[mkoncek]

By the way, in Fedora, the programmer does not have access to packaged rustup, but instead is supposed to install one of the additional rust-std-static-* packages (see: https://koji.fedoraproject.org/koji/buildinfo?buildID=2278881). But I don't think the upstream Rust project can / should / wants to detect such cases.

[Angelin01]

I can probably whip this up by tomorrow, already have the bash one ready, just need to do some testing with the ZSH one.

[Angelin01]

@rustbot claim