[error] Implement core::error::Error for errors (#1663)

.github/workflows/ci.yml

@@ -54,6 +54,7 @@ jobs:
           # These are the names of specific Rust versions detected in
           # `build.rs`. Each of these represents the minimum Rust version for
           # which a particular feature is supported.
+          "zerocopy-core-error",
           "zerocopy-generic-bounds-in-const-fn",
           "zerocopy-target-has-atomics",
           "zerocopy-aarch64-simd",
@@ -87,6 +88,8 @@ jobs:
             features: "--all-features"
           - toolchain: "stable"
             features: "--all-features"
+          - toolchain: "zerocopy-core-error"
+            features: "--all-features"
           - toolchain: "zerocopy-generic-bounds-in-const-fn"
             features: "--all-features"
           - toolchain: "zerocopy-target-has-atomics"
@@ -107,6 +110,8 @@ jobs:
           # other than "msrv", "stable", and "nightly". These other versions
           # exist to exercise zerocopy behavior which differs by toolchain;
           # zerocopy-derive doesn't behave different on these toolchains.
+          - crate: "zerocopy-derive"
+            toolchain: "zerocopy-core-error"
           - crate: "zerocopy-derive"
             toolchain: "zerocopy-generic-bounds-in-const-fn"
           - crate: "zerocopy-derive"
@@ -137,7 +142,28 @@ jobs:
             target: "thumbv6m-none-eabi"
           - toolchain: "zerocopy-aarch64-simd"
             target: "wasm32-wasi"
-          # Exclude most targets targets from the
+          # Exclude most targets targets from the `zerocopy-core-error`
+          # toolchain since the `zerocopy-core-error` feature is unrelated to
+          # compilation target. This only leaves i686 and x86_64 targets.
+          - toolchain: "zerocopy-core-error"
+            target: "arm-unknown-linux-gnueabi"
+          - toolchain: "zerocopy-core-error"
+            target: "aarch64-unknown-linux-gnu"
+          - toolchain: "zerocopy-core-error"
+            target: "powerpc-unknown-linux-gnu"
+          - toolchain: "zerocopy-core-error"
+            target: "powerpc64-unknown-linux-gnu"
+          - toolchain: "zerocopy-core-error"
+            target: "riscv64gc-unknown-linux-gnu"
+          - toolchain: "zerocopy-core-error"
+            target: "s390x-unknown-linux-gnu"
+          - toolchain: "zerocopy-core-error"
+            target: "x86_64-pc-windows-msvc"
+          - toolchain: "zerocopy-core-error"
+            target: "thumbv6m-none-eabi"
+          - toolchain: "zerocopy-core-error"
+            target: "wasm32-wasi"
+            # Exclude most targets targets from the
           # `zerocopy-generic-bounds-in-const-fn` toolchain since the
           # `zerocopy-generic-bounds-in-const-fn` feature is unrelated to
           # compilation target. This only leaves i686 and x86_64 targets.

Cargo.toml

@@ -32,6 +32,9 @@ exclude = [".*"]
 # as high as the specified version. In the emitted `--cfg`, dashes are replaced
 # by underscores.
 
+# From 1.81.0, Rust supports the `core::error::Error` trait.
+zerocopy-core-error = "1.81.0"
+
 # From 1.61.0, Rust supports generic types with trait bounds in `const fn`.
 zerocopy-generic-bounds-in-const-fn = "1.61.0"
 

build.rs

@@ -60,6 +60,11 @@ use std::{env, fs, process::Command, str};
 fn main() {
     // Avoid unnecessary re-building.
     println!("cargo:rerun-if-changed=build.rs");
+    // This is necessary because changes to the list of detected Rust toolchain
+    // versions will affect what `--cfg`s this script emits. Without this,
+    // changes to that list have no effect on the build without running `cargo
+    // clean` or similar.
+    println!("cargo:rerun-if-changed=Cargo.toml");
 
     let version_cfgs = parse_version_cfgs_from_cargo_toml();
     let rustc_version = rustc_version();

src/error.rs

@@ -65,6 +65,11 @@ use core::{
     ops::Deref,
 };
 
+#[cfg(zerocopy_core_error)]
+use core::error::Error;
+#[cfg(all(not(zerocopy_core_error), any(feature = "std", test)))]
+use std::error::Error;
+
 use crate::{util::SendSyncPhantomData, KnownLayout, TryFromBytes};
 #[cfg(doc)]
 use crate::{FromBytes, Ref};
@@ -126,9 +131,8 @@ impl<A: fmt::Display, S: fmt::Display, V: fmt::Display> fmt::Display for Convert
     }
 }
 
-#[cfg(any(feature = "std", test))]
-#[allow(clippy::std_instead_of_core)]
-impl<A, S, V> std::error::Error for ConvertError<A, S, V>
+#[cfg(any(zerocopy_core_error, feature = "std", test))]
+impl<A, S, V> Error for ConvertError<A, S, V>
 where
     A: fmt::Display + fmt::Debug,
     S: fmt::Display + fmt::Debug,
@@ -228,9 +232,8 @@ where
     }
 }
 
-#[cfg(any(feature = "std", test))]
-#[allow(clippy::std_instead_of_core)]
-impl<Src, Dst: ?Sized> std::error::Error for AlignmentError<Src, Dst>
+#[cfg(any(zerocopy_core_error, feature = "std", test))]
+impl<Src, Dst: ?Sized> Error for AlignmentError<Src, Dst>
 where
     Src: Deref,
     Dst: KnownLayout,
@@ -353,9 +356,8 @@ where
     }
 }
 
-#[cfg(any(feature = "std", test))]
-#[allow(clippy::std_instead_of_core)]
-impl<Src, Dst: ?Sized> std::error::Error for SizeError<Src, Dst>
+#[cfg(any(zerocopy_core_error, feature = "std", test))]
+impl<Src, Dst: ?Sized> Error for SizeError<Src, Dst>
 where
     Src: Deref,
     Dst: KnownLayout,
@@ -441,9 +443,8 @@ where
     }
 }
 
-#[cfg(any(feature = "std", test))]
-#[allow(clippy::std_instead_of_core)]
-impl<Src, Dst: ?Sized> std::error::Error for ValidityError<Src, Dst>
+#[cfg(any(zerocopy_core_error, feature = "std", test))]
+impl<Src, Dst: ?Sized> Error for ValidityError<Src, Dst>
 where
     Src: Deref,
     Dst: KnownLayout + TryFromBytes,