Regression in nightly-2026-05-04: `rustix` crate fails to build: attributes starting with `rustc` are reserved for use by the `rustc` compiler

[anforowicz]

Code

I tried this code:

$ cat Cargo.toml
[package]
name = "repro-2026-05-12"
version = "0.1.0"
edition = "2024"

[dependencies]
rustix="=0.37.28"

lukasza2 in /usr/local/google/home/lukasza/src/cargo/repro-2026-05-12
$ cat src/main.rs
fn main() {}

I expected to see this happen: This code should build fine.

Instead, this happened: This code fails to build with a recent nightly:

$ rustc --version
rustc 1.97.0-nightly (64a965e90 2026-05-11)

$ cargo build
   Compiling rustix v0.37.28
error: attributes starting with `rustc` are reserved for use by the `rustc` compiler
  --> /usr/local/google/home/lukasza/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/rustix-0.37.28/src/backend/linux_raw/io/errno.rs:28:25
   |
28 | #[cfg_attr(rustc_attrs, rustc_layout_scalar_valid_range_start(0xf001))]
   |                         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

error: attributes starting with `rustc` are reserved for use by the `rustc` compiler
  --> /usr/local/google/home/lukasza/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/rustix-0.37.28/src/backend/linux_raw/io/errno.rs:29:25
   |
29 | #[cfg_attr(rustc_attrs, rustc_layout_scalar_valid_range_end(0xffff))]
   |                         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

error: cannot find attribute `rustc_layout_scalar_valid_range_start` in this scope
  --> /usr/local/google/home/lukasza/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/rustix-0.37.28/src/backend/linux_raw/io/errno.rs:28:25
   |
28 | #[cfg_attr(rustc_attrs, rustc_layout_scalar_valid_range_start(0xf001))]
   |                         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

error: cannot find attribute `rustc_layout_scalar_valid_range_end` in this scope
  --> /usr/local/google/home/lukasza/.cargo/registry/src/index.crates.io-1949cf8c6b5b557f/rustix-0.37.28/src/backend/linux_raw/io/errno.rs:29:25
   |
29 | #[cfg_attr(rustc_attrs, rustc_layout_scalar_valid_range_end(0xffff))]
   |                         ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

error: could not compile `rustix` (lib) due to 4 previous errors

Version it worked on

cargo bisect-rustc says:

Regression in 684d04c. Note that if it is a legacy rollup build, it might be available in rust-lang-ci@684d04c.

The PR introducing the regression in this rollup is #155433: Rip out rustc_layout_scalar_valid_range_* attribute support

searched nightlies: from nightly-2026-04-27 to nightly-2026-05-12
regressed nightly: nightly-2026-05-04
searched commit range: 20de910...ad3a598
regressed commit: 818811b

bisected with cargo-bisect-rustc v0.6.11

Host triple: x86_64-unknown-linux-gnu
Reproduce with:

cargo bisect-rustc

Original bug

The original repro was using cargo to build bindgen in https://crbug.com/510018493. I guess the rustix-based repro can probably be reduced further, but hopefully this is enough to help start the investigation.

[anforowicz]

Oh, maybe this is already known - I see this problem being discussed in bytecodealliance/rustix#1620

[mejrs]

We've removed the rustc_layout_scalar_valid_range_* attributes. the replacement for them is https://doc.rust-lang.org/nightly/std/pat/macro.pattern_type.html

[anforowicz]

I see that this problem doesn't repro with rustix v1.1.4, so I think I'll close this issue as Working as Intended.