proc_macro attribue fails to expand when combined with cfg_attr

[TheButlah]

I have found that mixing certain atribute style proc macros fails when combined with cfg_attr and feature flags.
Link to minimally reproducible example

// This one works
#[safer_ffi::derive_ReprC]
#[ReprC::opaque]
pub struct NotGated {
    bar: String,
}

// This one doesn't work
#[cfg_attr(feature = "c_api", safer_ffi::derive_ReprC, ReprC::opaque)]
pub struct Gated {
    bar: String,
}

rust-analyzer version: rust-analyzer version: 0.4.1227-standalone

rustc version: rustc 1.66.0-nightly (ce7f0f1aa 2022-09-28) (please note its been broken for months, its not a recent regression)

relevant settings: "rust-analyzer.cargo.features": [ "c_api" ], and c_api is a default feature.

Original post before I got a minimal example (outdated)

Unfortunately I haven't been able to make a minimal reproducible example yet, but at least by making this issue I can bring some awareness.

I have a medium sized rust codebase, which uses macros quite a bit. There is one type here that never has autocomplete.

It is using proc-macros from safer-ffi and is cfg-gated. I haven't been able to figure out the root cause of the problem. I'll try to work a bit more on finding a minimal reproduction.

[bjorn3]

Have you told rust-analyzer to enable the c_api cargo feature? (using the rust-analyzer.cargo.features config if I recall correctly)

[TheButlah]

The feature is a default feature, so I shouldn't have to. But just to be sure, I checked my vscode workspace settings:

So it should work but doesn't

[bjorn3]

I see. Default features should remain enabled under rust-analyzer unless you explicitly disable them, so that is probably not the issue. Can you show a screenshot of the line with the derive? And can you also place the cursor at derive_ReprC and invoke the rust analyzer: expand macro command to check if macro expansion worked or not.

[TheButlah]

OK, I've created a minimally reproducible example, turns out it was easier than expected to minify. I've updated the original post.

[Veykril]

I believe the issue here is our expansion of the cfg_attr, we are most likely stripping the cfg_attr alltogether when transforming the struct to the token tree representation, so the macro doesn't get to see the ReprC::opaque.

[Dominator008]

Any fix / workaround for this? This makes vscode almost useless for a project I'm working on.

[mbuerki]

also still experiencing this problem. is some kind of fix already available? or in the making?