Confusing error message when proc macro not built due to allTargets: false

[bjorn3]

rust-analyzer version: rust-analyzer version: 0.3.2188-standalone [/home/bjorn/.vscode/extensions/rust-lang.rust-analyzer-0.3.2188-linux-x64/server/rust-analyzer]

rustc version: rustc 1.82.0 (f6e511eec 2024-10-15)

editor or extension: VSCode

relevant settings:

{
    "rust-analyzer.cargo.allTargets": false
}

repository link (if public, optional): (eg. rust-analyzer)

code snippet to reproduce:

#- Cargo.toml
[package]
name = "rust_analyzer_reproducer"
version = "0.1.0"
edition = "2021"

[dev-dependencies]
serde = { version = "1.0.215", features = ["derive"] }

//- tests/foo.rs
#[derive(serde::Serialize)]
struct Foo;

and then after rust-analyzer has started make any change to struct Foo;. This will result in a "proc-macro crate build data is missing dylib path" error. This doesn't make it clear that this is because disabling --all-targets prevents serde_derive from getting built as it is a dev-dependency. It also shouldn't show up as an error, but closer to the diagnostic that is shown when build script building is disabled entirely though preferably also explaining why the proc-macro wasn't built.

[ChayimFriedman2]

I'm not sure how we could detect that if --all-targets will be enabled the proc macro will be available. The downgrade in severity is possible, though.

[bjorn3]

We can detect that the proc macro dependency is a dev-dependency, right? All proc macros that are only reachable through a dev-dependency edge in the dependency graph are only available when --all-targets or similar is passed.

[ChayimFriedman2]

I don't think we can detect that, we don't know about dev dependencies, only about dependencies in the current configuration. Maybe we can add this but I don't know if this information is available to us from Cargo.

[bjorn3]

cargo metadata most certainly reports dev-dependencies. Otherwise rust-analyzer wouldn't even know to expect a proc macro here and thus complain about missing data for the proc macro. Not setting --all-targets only causes the cargo check invocation that rust-analyzer does to run build script amd build proc macro to omit artifact notifications for proc macros that are dev-dependencies.

[Veykril]

Our HIR layer doesn't know about dev dependencies (intentionally) iirc

[jerusdp]

If you are loading the dependencies from a workspace you don't know whether how they are used.

[Veykril]

I think thanks to --compile-time-deps we can ignore that setting for build scripts entirely and always pass --all-targets. We never try to build artifacts that may not built for the target with that flag anyways: #20159