`rustix::io::Errno` impl `core::error::Error` only with nightly

[dmitry-salin]

Support for error_in_core in no_std context was added in #1241 But it seems the use_feature_or_nothing("error_in_core"); check in build.rs requires nightly even with rust 1.81+.

❯ rustc --version
rustc 1.85.0 (4d91de4e4 2025-02-17)

Cargo.toml

[package]
name = "error"
version = "0.1.0"
edition = "2024"

[dependencies]
rustix = { version = "1.1.2", default-features = false }

main.rs

#![no_std]

use rustix::io::Errno;

use core::error::Error;

fn use_err<E: Error>(err: E) {}

fn main() {
    use_err(Errno::ACCESS);
}

cargo build

error[E0277]: the trait bound `Errno: core::error::Error` is not satisfied
  --> src/main.rs:10:13
   |
10 |     use_err(Errno::ACCESS);
   |     ------- ^^^^^^^^^^^^^ the trait `core::error::Error` is not implemented for `Errno`
   |     |
   |     required by a bound introduced by this call
   |
note: required by a bound in `use_err`
  --> src/main.rs:7:15
   |
7  | fn use_err<E: Error>(err: E) {}
   |               ^^^^^ required by this bound in `use_err`