Remove uses of feature(rustc_attrs)

.github/.cspell/project-dictionary.txt

@@ -37,7 +37,6 @@ IXUSR
 lseek
 musicpal
 nlink
-nonnull
 norvc
 nsec
 OMAP

build.rs

@@ -32,10 +32,6 @@ fn main() {
         }
     };
 
-    if version.nightly && is_allowed_feature("rustc_attrs") {
-        println!("cargo:rustc-cfg=semihosting_unstable_rustc_attrs");
-    }
-
     if target_arch == "arm" {
         if target.starts_with("thumb") {
             target_feature_if("thumb-mode", true, &version, None, true)
@@ -129,21 +125,6 @@ fn target_feature_if(
     }
 }
 
-fn is_allowed_feature(name: &str) -> bool {
-    // allowed by default
-    let mut allowed = true;
-    if let Some(rustflags) = env::var_os("CARGO_ENCODED_RUSTFLAGS") {
-        for mut flag in rustflags.to_string_lossy().split('\x1f') {
-            flag = flag.strip_prefix("-Z").unwrap_or(flag);
-            if let Some(flag) = flag.strip_prefix("allow-features=") {
-                // If it is specified multiple times, the last value will be preferred.
-                allowed = flag.split(',').any(|allowed| allowed == name);
-            }
-        }
-    }
-    allowed
-}
-
 mod version {
     use std::{env, process::Command, str};
 

src/fd.rs

@@ -36,16 +36,6 @@ static_assert!(core::mem::size_of::<RawFd>() == core::mem::size_of::<u16>());
 /// value `-1`.
 #[derive(Copy, Clone)]
 #[repr(transparent)]
-#[cfg_attr(semihosting_unstable_rustc_attrs, rustc_layout_scalar_valid_range_start(0))]
-#[cfg_attr(
-    all(semihosting_unstable_rustc_attrs, not(target_pointer_width = "16")),
-    rustc_layout_scalar_valid_range_end(0xFF_FF_FF_FE)
-)]
-#[cfg_attr(
-    all(semihosting_unstable_rustc_attrs, target_pointer_width = "16"),
-    rustc_layout_scalar_valid_range_end(0xFF_FE)
-)]
-#[cfg_attr(semihosting_unstable_rustc_attrs, rustc_nonnull_optimization_guaranteed)]
 pub struct BorrowedFd<'fd> {
     fd: RawFd,
     _phantom: PhantomData<&'fd OwnedFd>,
@@ -60,16 +50,6 @@ pub struct BorrowedFd<'fd> {
 /// passed as a consumed argument or returned as an owned value, and it never
 /// has the value `-1`.
 #[repr(transparent)]
-#[cfg_attr(semihosting_unstable_rustc_attrs, rustc_layout_scalar_valid_range_start(0))]
-#[cfg_attr(
-    all(semihosting_unstable_rustc_attrs, not(target_pointer_width = "16")),
-    rustc_layout_scalar_valid_range_end(0xFF_FF_FF_FE)
-)]
-#[cfg_attr(
-    all(semihosting_unstable_rustc_attrs, target_pointer_width = "16"),
-    rustc_layout_scalar_valid_range_end(0xFF_FE)
-)]
-#[cfg_attr(semihosting_unstable_rustc_attrs, rustc_nonnull_optimization_guaranteed)]
 pub struct OwnedFd {
     fd: RawFd,
 }

src/lib.rs

@@ -238,11 +238,11 @@ semihosting = { version = "0.1", features = ["stdio", "panic-handler"] }
     )),
     feature(asm_experimental_arch)
 )]
-#![cfg_attr(semihosting_unstable_rustc_attrs, feature(rustc_attrs))]
 #![cfg_attr(docsrs, feature(doc_cfg))]
 #![allow(clippy::empty_loop)] // this crate is #![no_std]
 #![allow(clippy::len_without_is_empty, clippy::new_without_default)]
 
+// TODO: mips32r6, mips64r6?
 #[cfg(not(any(
     target_arch = "aarch64",
     target_arch = "arm",