util: Support impl Error for Arc<T: Error> in no-std at Rust 1.81+

portable-atomic-util/CHANGELOG.md

@@ -10,6 +10,8 @@ Note: In this file, do not use the hard wrap in the middle of a sentence for com
 
 ## [Unreleased]
 
+- Support `impl Error for Arc<T: Error>` in no-std at Rust 1.81+.
+
 ## [0.2.0] - 2024-05-07
 
 - Rewrite `Arc` based on `std::sync::Arc`'s implementation. ([#142](https://github.com/taiki-e/portable-atomic/pull/142))

portable-atomic-util/build.rs

@@ -33,7 +33,7 @@ fn main() {
         // Custom cfgs set by build script. Not public API.
         // grep -E 'cargo:rustc-cfg=' build.rs | grep -v '=//' | sed -E 's/^.*cargo:rustc-cfg=//; s/(=\\)?".*$//' | LC_ALL=C sort -u | tr '\n' ','
         println!(
-            "cargo:rustc-check-cfg=cfg(portable_atomic_no_alloc,portable_atomic_no_alloc_layout_extras,portable_atomic_no_core_unwind_safe,portable_atomic_no_futures_api,portable_atomic_no_io_safety,portable_atomic_no_io_vec,portable_atomic_no_min_const_generics,portable_atomic_no_unsafe_op_in_unsafe_fn,portable_atomic_sanitize_thread)"
+            "cargo:rustc-check-cfg=cfg(portable_atomic_no_alloc,portable_atomic_no_alloc_layout_extras,portable_atomic_no_core_unwind_safe,portable_atomic_no_error_in_core,portable_atomic_no_futures_api,portable_atomic_no_io_safety,portable_atomic_no_io_vec,portable_atomic_no_min_const_generics,portable_atomic_no_unsafe_op_in_unsafe_fn,portable_atomic_sanitize_thread)"
         );
     }
 
@@ -72,6 +72,10 @@ fn main() {
     if !version.probe(63, 2022, 6, 15) {
         println!("cargo:rustc-cfg=portable_atomic_no_io_safety");
     }
+    // error_in_core stabilized in Rust 1.81 (nightly-2024-06-09): https://github.com/rust-lang/rust/pull/125951
+    if !version.probe(81, 2024, 6, 8) {
+        println!("cargo:rustc-cfg=portable_atomic_no_error_in_core");
+    }
 
     if version.nightly {
         // `cfg(sanitize = "..")` is not stabilized.

portable-atomic-util/src/arc.rs

@@ -2405,18 +2405,22 @@ fn data_offset_align(align: usize) -> usize {
     layout.size() + padding_needed_for(layout, align)
 }
 
-#[cfg(feature = "std")]
-impl<T: ?Sized + std::error::Error> std::error::Error for Arc<T> {
+#[cfg(not(portable_atomic_no_error_in_core))]
+use core::error;
+#[cfg(all(portable_atomic_no_error_in_core, feature = "std"))]
+use std::error;
+#[cfg(any(not(portable_atomic_no_error_in_core), feature = "std"))]
+impl<T: ?Sized + error::Error> error::Error for Arc<T> {
     #[allow(deprecated)]
     fn description(&self) -> &str {
-        std::error::Error::description(&**self)
+        error::Error::description(&**self)
     }
     #[allow(deprecated)]
-    fn cause(&self) -> Option<&dyn std::error::Error> {
-        std::error::Error::cause(&**self)
+    fn cause(&self) -> Option<&dyn error::Error> {
+        error::Error::cause(&**self)
     }
-    fn source(&self) -> Option<&(dyn std::error::Error + 'static)> {
-        std::error::Error::source(&**self)
+    fn source(&self) -> Option<&(dyn error::Error + 'static)> {
+        error::Error::source(&**self)
     }
 }