Closure #[target_feature] only checked during codegen

[hanna-kruppe]

I tried this code:

#![feature(stmt_expr_attributes)]

pub fn foo() {
    let f = #[target_feature(enable="magic")] || {};
    // f();
}

I expected to see this happen: error because the target feature does not exist and the closure is not unsafe.

Instead, this happened: the errors does not happen unless the closure is called in foo and foo is codegen'd. That is, I can get the expected errors by uncommenting the f(); line and running e.g. cargo build. but cargo check / rustc --emit metadata doesn't give any error, nor does cargo build give errors if foo is not codegen'd for other reasons (e.g., not pub in a library, or #[inline]).

Meta

rustc --version --verbose:

rustc 1.44.0-nightly (f509b26a7 2020-03-18)
binary: rustc
commit-hash: f509b26a7730d721ef87423a72b3fdf8724b4afa
commit-date: 2020-03-18
host: x86_64-unknown-linux-gnu
release: 1.44.0-nightly
LLVM version: 9.0

[hanna-kruppe]

I believe this is because rustc_passes::check_attr does not inspect target features on closures, as pointed out by @LeSeulArtichaut in #69274.