cargo bash-completion ignores `+toolchain` arg

[Rudxain]

Verification

• I searched for recent similar issues at https://github.com/rust-lang/rustup/issues?q=is%3Aissue and found no duplicates.
• I am on the latest version of Rustup according to https://github.com/rust-lang/rustup/tags and am still able to reproduce my issue.

Problem

If I type cargo +nightly run -- TAB in a project with MSRV, it starts downloading the MSRV, instead of using nightly as I explicitly specified

Steps

See summary

Possible Solution(s)

No response

Notes

No response

Rustup version

rustup 1.28.2 (e4f3ad6f8 2025-04-28)

Installed toolchains

Default host: x86_64-unknown-linux-gnu
rustup home:  /home/rudxain/.rustup

installed toolchains
--------------------
nightly-x86_64-unknown-linux-gnu (active, default)
1.82.0-x86_64-unknown-linux-gnu

active toolchain
----------------
name: nightly-x86_64-unknown-linux-gnu
active because: it's the default toolchain
installed targets:
  x86_64-unknown-linux-gnu

OS version

Debian Testing

[djc]

By MSRV, do you mean, a rust-toolchain.toml file?

[rami3l]

Thanks for filing this issue!

Unfortunately, this is a known problem: due to a limitation in clap, it is completely unaware of the +toolchain syntax out of the box.

Recently there seems to have been a way to teach clap of this fact, but it would require some manual analysis and implementation to work correctly. Once #2268 is fixed, this should be solved at the same time.

As such, I'm closing this issue as a duplicate of #2268.

[rami3l]

Interestingly, this could be a useful argument against implicit installation in #4211 given that something as small as hitting the tab key can lead to unexpected response time...

At least it can align better with rust-lang/rust-analyzer#20719; not completely sure if clap can be taught to do that though.