Notify Users of cargo +nightly install when using cargo install +nightly

[DrRuhe]

Problem

When running cargo install +nightly ... there is no indication that it does not actually use the nightly toolchain, until the compilation runs into errors because e.g. features need nightly.

Proposed Solution

Either:
Let the user know that cargo install +nightly ... doesn't actually use nightly and instead they should use cargo +nightly install ....

Or:
just use nightly...

Notes

No response

[weihanglo]

Should be fairly easy to tackle for only cargo install. That being said, I personally want a solution for all cargo commands. People may also type cargo build +nightly and we should catch that. The difficult part is that rustup proxy name can be custom defined.

If we got #11702 or clap-rs/clap#4706 landed, I think it's sufficient that we target only a subset of most common ones like +stable, +beta, +nightly.

[epage]

The problem is +<channel> isn't a flag per se but a positional argument.

cargo install and cargo add are some of the few commands that even accept a positional argument, so I can see doing this in a one-off way.

(some others accept positional arguments but those are just meant to forward to an underlying command)

[weihanglo]

cargo install and cargo add are some of the few commands that even accept a positional argument, so I can see doing this in a one-off way.

Agree with that. cargo run is a thing that we probably cannot fix at this moment.

Here are some pointers where cargo install and cargo add collect their positional arguments

• cargo/src/bin/cargo/commands/add.rs

  Lines 239 to 244 in 58b22f0

  	let mut crates = matches
  	.get_many::<String>("crates")
  	.into_iter()
  	.flatten()
  	.map(|c| (Some(c.clone()), None))
  	.collect::<IndexMap<_, _>>();

• cargo/src/bin/cargo/commands/install.rs

  Lines 105 to 109 in 58b22f0

  	let krates = args
  	.get_many::<String>("crate")
  	.unwrap_or_default()
  	.map(|k| resolve_crate(k, version))
  	.collect::<crate::CargoResult<Vec<_>>>()?;

I think Cargo can send an ad-hoc error message when detecting any crate starting with +. Something like,

error: invalid character `+` in package name: `nightly`
     Use `cargo +nightly add` if you meant to use `nightly` toolchain.

(you could find a better message than mine)

[danilhendrasr]

Hi, I would like to take on this issue. But, just to confirm, from what I understand in order to resolve this issue we only need to make cargo emits the above error message whenever the add and install command is run with a crate name that has + in it. Is it correct?

[weihanglo]

That's exactly my plan so far!

You may want to tweak the message a bit. Mine is not as good as it looks.

[danilhendrasr]

Got it, I'll see what I can come up with.

@rustbot claim

[danilhendrasr]

I think I need more clarification.

If the error is emitted any time the command is given a crate name that starts with + regardless if the rest of the crate name is actually the same as one of the three toolchain channels name (stable, beta, nightly), then the following part:

  Use `cargo +<crate name> add` if you meant to use `<crate name>` toolchain.

of the error should only be printed if the rest of crate name after the + sign is actually the same as one of the three toolchain channels name.
Is that correct?

[weihanglo]

Toolchain name can be anything, such like cargo +stage1 build.

My best guess is, from the array of crates name strings (krates and crates in source code), if there is a string starting with +, give the user an error.