cargo reports a warning: panic setting is ignored for bench profile. When the value it is not ignored.

[zeroflaw]

Problem

cargo bench fails to compile when using build-std, however including 'panic = "unwind"' in Cargo.toml '[profile.bench]' fixes the issue. This causes cargo to warn about the setting being ignored, when it's clearly doing something.

Steps

versions:

rustc 1.80.0-nightly (87293c958 2024-05-08)
cargo 1.80.0-nightly (0ca60e940 2024-05-08)

~/.cargo/config.toml

[build]
rustflags = [
  "-C", "panic=abort",
  "-Z", "panic-in-drop=abort",
  "-Z", "panic_abort_tests",
]
target = "x86_64-unknown-linux-gnu"

[unstable]
build-std = ["core,alloc,std,panic_abort"]
build-std-features = []

/project/Cargo.toml

[workspace]
resolver = "2"
members = [ 
#snip
]

[profile.bench]
lto = true
codegen-units = 1
panic = "unwind"

[profile.release]
lto = true
codegen-units = 1
panic = "abort"

bench.rs

#![feature(test)]
extern crate test;

#[bench]
fn bench_a_thing(b: &mut test::Bencher) {
//snip
}

cargo bench without 'panic = "unwind"' in Cargo.toml '[profile.bench]'

error: the `#[alloc_error_handler]` in std conflicts with allocation error handler in: std

error[E0152]: duplicate lang item in crate `std` (which `test` depends on): `panic_impl`.

cargo bench with 'panic = "unwind"' in Cargo.toml '[profile.bench]'

warning: /project/Cargo.toml: `panic` setting is ignored for `bench` profile

bench run successful.

Possible Solution(s)

suppress / remove the warning, panic setting is ignored for bench profile

Notes

No response

Version

No response

[ehuss]

Cargo is not expecting the panic setting to be overridden via RUSTFLAGS. Generally, any rustc flag that cargo needs to control (such as all of those in the profile) should not be specified in RUSTFLAGS.

[zeroflaw]

~/.cargo/config.toml

[build]
rustflags = [
  "-Z", "panic-in-drop=abort",
]
target = "x86_64-unknown-linux-gnu"

[unstable]
build-std = ["core,alloc,std"]

cargo bench without 'panic = "unwind"' in Cargo.toml '[profile.bench]'

error: the `#[alloc_error_handler]` in std conflicts with allocation error handler in: std

error: the crate `panic_unwind` does not have the panic strategy `unwind`

error[E0152]: duplicate lang item in crate `std` (which `test` depends on): `panic_impl`.

cargo bench with 'panic = "unwind"' in Cargo.toml '[profile.bench]'

warning: /project/Cargo.toml: `panic` setting is ignored for `bench` profile
    Finished `bench` profile [optimized] target(s) in 0.10s

Issue still occurs when I remove "-C", "panic=abort", from RUSTFLAGS.

'panic = "unwind"' in Cargo.toml '[profile.bench]' is not being ignored because if I set it to abort I get the same error as before. If changing the value changes the behaviour, how is it ignored?

edit: If I don't have any RUSTFLAGS in ~/.cargo/config.toml I get the same error/warning