Impl Error for CoseError under std feature

.github/workflows/ci.yml

@@ -28,6 +28,7 @@ jobs:
           components: rustfmt
           override: true
       - run: cargo build --release --workspace
+      - run: cargo build --release --workspace --features=std
 
   test:
     runs-on: ubuntu-latest
@@ -48,6 +49,7 @@ jobs:
           components: rustfmt
           override: true
       - run: cargo test --workspace -- --nocapture
+      - run: cargo test --workspace --features=std -- --nocapture
 
   examples:
     runs-on: ubuntu-latest
@@ -68,6 +70,7 @@ jobs:
           components: rustfmt
           override: true
       - run: cargo test --examples
+      - run: cargo test --features=std --examples
 
   no_std:
     name: Build for a no_std target
@@ -107,6 +110,7 @@ jobs:
           components: rustfmt
           override: true
       - run: rustc --version
+      - run: cargo build --release --workspace
       - run: cargo build --release --workspace --all-features
 
   formatting:

Cargo.toml

@@ -9,6 +9,11 @@ repository = "https://github.com/google/coset"
 keywords = ["cryptography", "cose"]
 categories = ["cryptography"]
 
+[features]
+default = []
+# `std` feature enables an `Error` impl for `CoseError`
+std = []
+
 [dependencies]
 ciborium = { version = "^0.2.0", default-features = false }
 ciborium-io = { version = "^0.2.0", features = ["alloc"] }

src/common/mod.rs

@@ -87,6 +87,9 @@ impl core::fmt::Display for CoseError {
     }
 }
 
+#[cfg(feature = "std")]
+impl std::error::Error for CoseError {}
+
 impl CoseError {
     fn fmt_msg(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
         match self {

src/lib.rs

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

src/util/mod.rs

@@ -164,6 +164,7 @@ 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(_) => {