Give a more helpful error message for `rustup which rustfmt` if it's not installed

[jyn514]

Problem you are trying to solve

These errors are inconsistent:

; rustup which rustfmt --toolchain beta
error: not a file: '/home/jyn/.local/lib/rustup/toolchains/beta-x86_64-unknown-linux-gnu/bin/rustfmt'
; rustfmt +beta
error: 'rustfmt' is not installed for the toolchain 'beta-x86_64-unknown-linux-gnu'
To install, run `rustup component add rustfmt --toolchain beta-x86_64-unknown-linux-gnu`

Solution you'd like

The second error here ('rustfmt not installed') seems more helpful; it would be nice to show that consistently.

Notes

; rustup --version
rustup 1.26.0 (5af9b9484 2023-04-05)

Note that this error message also happens for commands which aren't proxied:

; rustup which ls --toolchain beta
error: not a file: '/home/jyn/.local/lib/rustup/toolchains/beta-x86_64-unknown-linux-gnu/bin/ls'

I'm not sure the right thing to do here; maybe the current error is good enough?

[jyn514]

This also applies to rustup man:

; rustup man --toolchain 1.55 rustc
error: not a directory: '/home/jyn/.local/lib/rustup/toolchains/1.55-x86_64-unknown-linux-gnu/share/man'

[Bogay]

Hi, I'm interested in working on this issue and have been exploring the related code. I've made some modifications to rustup which and here are examples of the error messages from my current version:

; ./home/bin/rustup which --toolchain custom rustfm
error: toolchain 'custom' is not installed

; ./home/bin/rustup which ls
error: Unknown binary 'ls' in toolchain 'stable-x86_64-unknown-linux-gnu'.

; ./home/bin/rustup which rustfmt
/home/bogay/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/bin/rustfmt

; ./home/bin/rustup which rustfmt
error: 'rustfmt' is not installed for the toolchain 'stable-x86_64-unknown-linux-gnu'.

But I am not sure about the implementation to keep error message consistent, the error msg To install, run ... seems originates from DistributableToolchain::recursion_error:

rustup/src/toolchain/distributable.rs

Lines 455 to 457 in 658d317

	Err(anyhow!(
	"'{binary_lossy}' is not installed for the toolchain '{desc}'.\nTo install, run `rustup component add {selector}{component_name}`"
	))

I've considered a few approaches for handling this:

1. copy-paste the error message: make the error message consistent, but repeat the error message in code twice
2. reuse DistributableToolchain::recursion_error: this centralizes the error message definition, but I'm not sure if it's the right semantic fit for rustup which
3. extract the error to src/error.rs: like RustupError::ToolchainNotInstalled, maybe I can add an error e.g. RustupError::ComponentNotInstalled

I lean towards the third option as it seems the cleanest architecturally. However, I'm not fully confident in my understanding of rustup's component management to design the error structure perfectly. Additionally, I'm wondering if adding a new variant to RustupError would be a breaking change, given that it doesn't appear to be marked #[non_exhaustive].

Any guidance or thoughts on these options would be greatly appreciated!

[djc]

You're far enough along that I'd recommend just submitting a PR so we can have a look at the code and go from there!

[Bogay]

I opened a draft PR #4429. It updates the error message as per the issue description. But some edge cases are not coverd, e.g. if a binary is expected to be provided by a component but not found on disk. (which is handled in DistributableToolchain::recursion_error)

Any feedback is appreciated!

[Bogay]

This also applies to rustup man:

; rustup man --toolchain 1.55 rustc
error: not a directory: '/home/jyn/.local/lib/rustup/toolchains/1.55-x86_64-unknown-linux-gnu/share/man'

I've tested this scenario. Because rustup currently downloads missing toolchain by default, and report missing toolchain if not installed. I think it might be considered resolved now? At least we won't see this error message in most cases.

❯ RUSTUP_AUTO_INSTALL=0 ./home/bin/rustup man --toolchain 1.70 rustc
error: toolchain '1.70-x86_64-unknown-linux-gnu' is not installed
help: run `rustup toolchain install 1.70-x86_64-unknown-linux-gnu` to install it