Move to use core version of Error

.github/workflows/ci.yml

@@ -93,7 +93,7 @@ jobs:
     strategy:
       fail-fast: false
       matrix:
-        rust: [1.58.0, 1.59.0]
+        rust: [1.81.0, 1.82.0]
     steps:
       - uses: actions/checkout@8e5e7e5ab8b370d6c329ec480221332ada57f0ab # v3.5.2
         with:

Cargo.toml

@@ -1,17 +1,21 @@
 [package]
 name = "coset"
-version = "0.4.0"
+version = "0.4.1"
 authors = ["David Drysdale <[email protected]>", "Paul Crowley <[email protected]>"]
 edition = "2018"
 license = "Apache-2.0"
 description = "Set of types for supporting COSE"
 repository = "https://github.com/google/coset"
 keywords = ["cryptography", "cose"]
 categories = ["cryptography"]
+rust-version = "1.81"
 
 [features]
 default = []
-# `std` feature enables an `Error` impl for `CoseError`
+
+# The `std` feature is maintained for back-compatibility; it previously enabled a
+# `std::error::Error` impl for `CoseError`, but the code now (always) has a
+# `core::error::Error` impl.
 std = []
 
 [dependencies]

README.md

@@ -15,15 +15,17 @@ example](examples/signature.rs) for documentation on how to use the code.
 
 ## Features
 
-The `std` feature of the crate enables an implementation of `std::error::Error` for `CoseError`.
+The `std` feature of the crate does nothing, and is maintained for back-compatibility.  (It previously
+enabled an implementation of `std::error::Error` for `CoseError`, but there is now an implementation
+of `core::error::Error` that is always present.)
 
 ## `no_std` Support
 
 This crate supports `no_std` (when the `std` feature is not set, which is the default), but uses the `alloc` crate.
 
 ## Minimum Supported Rust Version
 
-MSRV is 1.58.
+MSRV is 1.81.
 
 ## Integer Ranges
 

src/common/mod.rs

@@ -95,8 +95,7 @@ impl core::fmt::Display for CoseError {
     }
 }
 
-#[cfg(feature = "std")]
-impl std::error::Error for CoseError {}
+impl core::error::Error for CoseError {}
 
 impl CoseError {
     fn fmt_msg(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {

src/lib.rs

@@ -96,7 +96,7 @@
 //! [COSE]: https://tools.ietf.org/html/rfc8152
 //! [CBOR]: https://tools.ietf.org/html/rfc7049
 
-#![cfg_attr(not(feature = "std"), no_std)]
+#![no_std]
 #![deny(rustdoc::broken_intra_doc_links)]
 extern crate alloc;
 

src/util/mod.rs

@@ -164,7 +164,6 @@ pub fn expect_err<T: core::fmt::Debug, E: core::fmt::Debug + core::fmt::Display>
     result: Result<T, E>,
     err_msg: &str,
 ) {
-    #[cfg(not(feature = "std"))]
     use alloc::format;
     match result {
         Ok(_) => {