"rust-analyzer failed to discover workspace" could be so much more helpful

[matklad]

Today I've got to help a new Rust user to start their Rust project, and our logic to discovering Cargo.tomls was a huge roadblock. Comically gigantic I would say even :)

Basically, the project was in the subdir of the subdir, so nothing worked. But I wasn't able to diagnose on the spot! I had to do the "ok, let's create a new hello-world project and see if it works there" dance to debug this (and it was actually the person whom I was trying to help who said "huh, maybe the problem is that Cargo.toml is in a subdirectory?")

Here's a bunch of ways we can improve this:

• if there are no projects, we should show red/yellow status.
• in the status, and in the "rust-analyzer failed to discover workspace" error notification, we should say HOW TO ACTUALLY FIX THE PROBLEM (it's ridiculous that we don't do this, seeing this message from the newbie eyes really is painful)
• at minimum, we should point at the linked projects settings
• ideally, as suggested to me, there should be an "open Cargo.toml" link which opens open file dialog
• and, yeah, it would be cool to suggesting adding Cargo.toml to linked projects if we notice it some time after opening a project (eg, opening a Rust file).

[DrChat]

On this line of thought - I had some prototype work that added logic to search for all Cargo.toml manifests in the workspace folder tree and then filter them out using cargo metadata so that ProjectManifest::discover returned all workspace root manifests.
Would something like that be useful for including upstream? Is it too costly to call cargo manifest when scanning for projects?

Also related to #9661

[plwalsh]

@matklad Did something in the extension change recently that now prevents it from auto-discovering projects that aren't at the root of the vscode workspace? I could've sworn it was working fine before the last week or two. But now I see the "failed to discover workspace" message every time I open vscode (with my Rust project is two levels down). I'm on the latest insiders release, with the extension set to the pre-release channel.

[matklad]

We only auto-discover Rust projects one-level deep.

[plwalsh]

@matklad Interesting -- thanks!

[zirconium-n]

We only auto-discover Rust projects one-level deep.

Could we change this to a configurable depth?

[plwalsh]

Could we change this to a configurable depth?

Yes, please. Something like the recently implemented git.repositoryScanMaxDepth would be great (microsoft/vscode#37947).

Most often, my vscode workspace is a collection of clones, with several of the nested clones being Rust projects. Previously with RLS (before switching to rust-analyzer), all the nested Rust projects would automatically be "discovered", and I'd have access to all the RLS tools any time a Rust file was opened. Now with RA, I have no features available in my opened Rust files. Unfortunately, all my workspaces are different/dynamic, so keeping track of them all as rust-analyzer.linkedProjects isn't really tenable.

[bjorn3]

For activating the extension, I don't think so. It isn't possible to change the activationEvents of an extension:

rust-analyzer/editors/code/package.json

Line 63 in 61504c8

"workspaceContains:*/Cargo.toml",

When you open a rust file it should still activate though. For once the extension is activated, possibly:

rust-analyzer/crates/project-model/src/lib.rs

Lines 122 to 131 in 61504c8

	fn find_cargo_toml_in_child_dir(entities: ReadDir) -> Vec<ManifestPath> {
	// Only one level down to avoid cycles the easy way and stop a runaway scan with large projects
	entities
	.filter_map(Result::ok)
	.map(|it| it.path().join("Cargo.toml"))
	.filter(|it| it.exists())
	.map(AbsPathBuf::assert)
	.filter_map(|it| it.try_into().ok())
	.collect()
	}

[samgqroberts]

Is there a way to manually resolve this? I have my workspace Cargo.toml a few directories deep in my project. I've scanned the extension settings and can't find a place to manually point rust-analyzer to a Cargo.toml. It seems my only option is to open the subfolder as the root of my VSCode project when I'm working in the Rust portion of it, and switch back to a VSCode window that's at the actual root of my repository for the rest. I've confirmed this works, but it's certainly not ideal.

[matklad]

https://rust-analyzer.github.io/manual.html#rust-analyzer.linkedProjects

[samgqroberts]

That was it! Thank you @matklad