Rust-analyzer version is outdated

[numero-744]

For instance, if one uses std::iter::repeat_n(t, n), with current stable channel, it compiles but YCM claims with an Error diagnostic that it is unstable.
(If you use repeat(t).take(n) instead, cargo clippy even warns you that you should use repeat_n now!)

It would be nice to use either stable, or better, to use the version of rust-analyzer which is already installed user-wide by rustup.
This way the diagnostics provided in vim would always be the same than those provided by commands such as cargo check.
Also, it would avoid installing rust-analyzer twice.

[puremourning]

You can set the path to rust toolchain in settings.

[numero-744]

Thanks, I am able to choose the stable channel, but I have no idea how to use the already rustup-installed program instead. I could open a PR to make it default for new users. Or maybe: if INSTALLED found then use it else install from stable. But maybe it would be better to do: if INSTALLED found then use it else error out with the rustup command to install rust-analyzer?

[puremourning]

Just supply the toolchain path in vim settings according to the YCM docs.

We will not change our policy of only updating ra to versions we know work and pass our tests.

We would welcome a PR which updated ra to a stable version that passss our tests but not one that randomly picks a version and hopes it works as that's exactly what the setting is for.

https://github.com/ycm-core/YouCompleteMe?tab=readme-ov-file#the-gycm_rust_toolchain_root-option

[numero-744]

Okay I understand your point about testing.

I think this explanation would be worth adding in the Rust-related installation part of the README: the default is guaranteed to be compatible with YCM, but diagnostics can differ from the CLI; and maybe point to the configuration option?

To help future users, I could add to the docs of the configuration option:

• The default rustup path let g:ycm_rust_toolchain_root='$HOME/.rustup/toolchains/stable-x86_64-unknown-linux-gnu'
• A warning that it is not possible to use neither $HOME nor ~ in the path: the complete path should be used instead.

Also, it seems I cannot run install.py without the --rust-completer flag to remove the additional install of rust-analyzer, it completely removes Rust support…
But after running install.py I can remove third_party/ycmd/third_party/rust-analyzer and it works.

[puremourning]

. A warning that it is not possible to use neither $HOME nor ~ in the path: the complete path should be used instead.

Not true, you can use expand() see :help expand.

I think the documentation is pretty clear, and if you want to do something off piste and advanced, then it's for advanced users. We also are not in th business of documenting third party things like cargo or rustup. That's the responsibility of the team that maintains those tools. The problem with adding to our docs is that it will constantly be wrong or out of data secondary source which is both confusing, frustrating and inefficient.

A simple note that we use a specific version of rust-analyser that is known to work and does not have game-breaking bugs, or non-backward compatible changes, which are common for this engine, is enough along with a link to the setting to point at your favourite toolchain and a warning that use of an arbitrary toolchain is unsupported.