Cargo-powered diagnostics fail silently when a dependency fails to build

[nightkr]

Repro

1. Set up a new project with broken dependencies (assuming cargo-edit and cargo-feature, otherwise do the Cargo.toml edits manually :P):

cargo new my-repro --bin
cd my-repro
cargo add [email protected] --no-default-features
# Only one version feature may be enabled at a time
cargo feature k8s-openapi +v1_16 +v1_17
# Confirm that it fails to build...
cargo build

2. Open in whatever Rust-Analyzer-powered editor you prefer (so far I've tested and confirmed emacs+lsp-mode and vscode+ra plugin)
3. Write some invalid code (such as adding a call to a missing asdf(); function to main)

Expected outcome

Rust-Analyzer reports an error building dependencies.

Actual outcome

Rust-Analyzer reports no errors, and displays the asdf(); call as a valid call of type {unknown}.

Well, duh, of course this doesn't work

This example is pretty contrived, but it's easy to get bit by in multi-crate workspaces. If you have multiple bin crates then they can end up with conflicting dependencies, which work fine when building any crate in isolation (such as running cargo run, or cargo build inside of the crate directory), but break when building the whole workspace (such as running cargo build in the workspace dir, or running Rust-Analyzer).

[theduke]

The issue started happening on master 1-2 weeks ago, and I see it regularly.

Note: this is apparently not exclusive to failing dependencies.
It also happens inside a single crate between modules.

It's extremely cumbersome during refactoring, since the issue seems to pop up especially when changing a lot (type signatures, moving modules around, ...).

[nightkr]

@theduke

Just to confirm that we're talking about the same issue... Are you talking about {unknown} showing up, or errors from rustc/cargo build missing in Rust-Analyzer? This issue also seems to be completely deterministic: it's unaffected by restarting Rust-Analyzer, the buffer, or the editor.

[theduke]

Are you talking about {unknown} showing up, or errors from rustc/cargo build missing in Rust-Analyzer?

The latter.

This issue also seems to be completely deterministic

This is the behaviour I'm seeing as well.

Things start to work again after fixing enough of the errors, and stop working when undoing those changes.

If it's helpful I can also try to find a minimal single-crate reproduction.

[lnicola]

This is more or less working after #8355:

I'll file a new issue for the ungreat error messages.