rust-analyzer and real-time linting

[sbromberger]

Sorry if this is a stupid question, but I've been hearing that rust-analyzer is a "drop-in replacement" for rls. However, I can't seem to get the same behavior in between rls and rust-analyzer in vim. I've tried two different LSP clients: ALE and coc.nvim, and both of them show this crucial difference:

With rls, linting is "real-time"- that is, with ALE, I configure it to show me new errors whenever I exit insert mode. I type something, hit , and boom - if there's an error, I see it. I fix the problem, and the error notification goes away.

With rust-analyzer, I have to explicitly save the file before anything is linted. I then fix the problem, and have to save the file again for the error notification to disappear. (In the meantime, if I've removed or added a line, the highlight is now on a completely different line that has no error.)

Is this expected behavior, or am I configuring something incorrectly?

[matklad]

This is expected behavior. The full explanation can be found here: https://rust-analyzer.github.io/blog/2020/04/20/first-release.html#drawbacks.

We'll fix it eventually, by switching to as-you-type linting, but that's pretty far in the future. At the moment the work-around is to enable auto-save in the editor.

[sbromberger]

Thanks for the confirmation. Auto-save in the editor is not a great option, since I don't necessarily want regular writes to disk / remote network mounts.

I would agree that this is a pretty significant drawback, and one that would preclude use of rust-analyzer as a general LSP server until it's fixed. I'm glad to see that it's on the roadmap, though, but a bit concerned by the statement that it's pretty far in the future. Hopefully rls will still be supported until such time as this is implemented.

Appreciate the quick response!

[oblitum]

@sbromberger you can have both running at the same time, but it's not light on memory: #1710 (comment). I don't use that anymore, but it worked, coc.nvim with analyzer for anything LSP but diagnostics (you can leave it enabled too), and ALE for diagnostics (I think you may also use coc.nvim here too, just set one coc-extension/server-configuration to not have diagnostics, for example, having both coc-rust-analyzer and coc-rls, disable rust-analyzer.diagnostics.enable/rust-analyzer.rust-analyzer.checkOnSave.enable for the first and disable rust.racer_completion for the latter).

[nikitavoloboev]

Is this possible to achieve in VSCode Rust Analyser? I read this thread and still confused.

I am coming to Rust from Go/TypeScript where I had linting without manually pressing save and I really miss it in Rust.

I watched this video and in there he had a setup although in Vim that had this behavior. Is it possible to do with rust-analyser already?

[hichemfantar]

@matklad
Auto save is close except it should be auto lint/check
the way auto save works is via debouncing and cancelling the save timer each time the file changes.
It would be great if we had the same behavior but for a custom command (cargo check) instead save
the following:

{
	"files.autoSave": "afterDelay",
	"files.autoSaveDelay": 1000
}

can become: the solution below is customizable and if the project is very big, the user can simply increase the delay or turn it off completely for performance reasons. (this is all under the assumption that saving the file isn't required for linting)

{
	"rust-analyzer.autoCheck": "afterDelay",
	"rust-analyzer.autoCheckDelay": 1000,
}

[minhbear]

Hi guys, right now I had face that issue, the rust-analyzer does not check linting in realtime, when I run command cargo check it throw error and warning, eventhough I had config rust-analyze.linkedProject and enable autocheckonsave but it not work