Implement core::error::Error on Rust 1.81+

Cargo.toml

@@ -5,6 +5,8 @@ edition = "2018"
 keywords = ["object", "elf", "mach-o", "pe", "coff"]
 license = "Apache-2.0 OR MIT"
 repository = "https://github.com/gimli-rs/object"
+# NB: if this number increases to 1.81-or-later delete the `build.rs` script
+# as it's no longer necessary.
 rust-version = "1.65"
 description = "A unified interface for reading and writing object file formats."
 include = [

build.rs

@@ -0,0 +1,27 @@
+use std::process::Command;
+use std::str;
+
+fn main() {
+    // Temporary check to see if the rustc version >= 1.81 in which case the
+    // `Error` trait is always available. This is temporary because in the
+    // future the MSRV of this crate will be beyond 1.81 in which case this
+    // build script can be deleted.
+    let minor = rustc_minor_version().unwrap_or(0);
+    if minor >= 81 {
+        println!("cargo:rustc-cfg=core_error");
+    }
+    if minor >= 80 {
+        println!("cargo:rustc-check-cfg=cfg(core_error)");
+    }
+}
+
+fn rustc_minor_version() -> Option<u32> {
+    let rustc = std::env::var("RUSTC").unwrap();
+    let output = Command::new(rustc).arg("--version").output().ok()?;
+    let version = str::from_utf8(&output.stdout).ok()?;
+    let mut pieces = version.split('.');
+    if pieces.next() != Some("rustc 1") {
+        return None;
+    }
+    pieces.next()?.parse().ok()
+}

src/build/error.rs

@@ -24,6 +24,8 @@ impl fmt::Display for Error {
 
 #[cfg(feature = "std")]
 impl error::Error for Error {}
+#[cfg(all(not(feature = "std"), core_error))]
+impl core::error::Error for Error {}
 
 impl From<read::Error> for Error {
     fn from(error: read::Error) -> Error {

src/read/mod.rs

@@ -124,6 +124,8 @@ impl fmt::Display for Error {
 
 #[cfg(feature = "std")]
 impl std::error::Error for Error {}
+#[cfg(all(not(feature = "std"), core_error))]
+impl core::error::Error for Error {}
 
 /// The result type used within the read module.
 pub type Result<T> = result::Result<T, Error>;

src/write/mod.rs

@@ -60,6 +60,8 @@ impl fmt::Display for Error {
 
 #[cfg(feature = "std")]
 impl error::Error for Error {}
+#[cfg(all(not(feature = "std"), core_error))]
+impl core::error::Error for Error {}
 
 /// The result type used within the write module.
 pub type Result<T> = result::Result<T, Error>;