Stabilize no-std StdError trait

Author: dtolnay

serde/build.rs

@@ -15,6 +15,7 @@ fn main() {
 
     if minor >= 77 {
         println!("cargo:rustc-check-cfg=cfg(no_core_cstr)");
+        println!("cargo:rustc-check-cfg=cfg(no_core_error)");
         println!("cargo:rustc-check-cfg=cfg(no_core_net)");
         println!("cargo:rustc-check-cfg=cfg(no_core_num_saturating)");
         println!("cargo:rustc-check-cfg=cfg(no_core_try_from)");
@@ -98,6 +99,12 @@ fn main() {
     if minor < 78 {
         println!("cargo:rustc-cfg=no_diagnostic_namespace");
     }
+
+    // The Error trait became available in core in 1.81.
+    // https://blog.rust-lang.org/2024/09/05/Rust-1.81.0.html#coreerrorerror
+    if minor < 81 {
+        println!("cargo:rustc-cfg=no_core_error");
+    }
 }
 
 fn rustc_minor_version() -> Option<u32> {

serde/src/de/mod.rs

@@ -124,10 +124,10 @@ pub(crate) mod size_hint;
 
 pub use self::ignored_any::IgnoredAny;
 
-#[cfg(not(any(feature = "std", feature = "unstable")))]
+#[cfg(all(not(feature = "std"), no_core_error))]
 #[doc(no_inline)]
 pub use crate::std_error::Error as StdError;
-#[cfg(all(feature = "unstable", not(feature = "std")))]
+#[cfg(not(any(feature = "std", no_core_error)))]
 #[doc(no_inline)]
 pub use core::error::Error as StdError;
 #[cfg(feature = "std")]

serde/src/lib.rs

@@ -325,7 +325,7 @@ pub mod __private;
 #[path = "de/seed.rs"]
 mod seed;
 
-#[cfg(not(any(feature = "std", feature = "unstable")))]
+#[cfg(all(not(feature = "std"), no_core_error))]
 mod std_error;
 
 // Re-export #[derive(Serialize, Deserialize)].

serde/src/ser/mod.rs

@@ -115,10 +115,10 @@ mod impossible;
 
 pub use self::impossible::Impossible;
 
-#[cfg(not(any(feature = "std", feature = "unstable")))]
+#[cfg(all(not(feature = "std"), no_core_error))]
 #[doc(no_inline)]
 pub use crate::std_error::Error as StdError;
-#[cfg(all(feature = "unstable", not(feature = "std")))]
+#[cfg(not(any(feature = "std", no_core_error)))]
 #[doc(no_inline)]
 pub use core::error::Error as StdError;
 #[cfg(feature = "std")]