Add some annotations, plus a check for features

test.sh

@@ -33,6 +33,8 @@ if [ "$VALIDATE" -eq "1" ]; then
 # Validate --no-default-features build
 echo "________Validate build________"
 cargo check --no-default-features
+cargo check --manifest-path util/io/Cargo.toml --no-default-features
+cargo check --manifest-path util/io/Cargo.toml --features "mio"
 
 # Validate chainspecs
 echo "________Validate chainspecs________"

util/io/src/lib.rs

@@ -106,6 +106,7 @@ thread_local! {
 /// IO Error
 pub enum IoError {
  /// Low level error from mio crate
+ #[cfg(feature = "mio")]
  Mio(::std::io::Error),
  /// Error concerning the Rust standard library's IO subsystem.
  StdIo(::std::io::Error),
@@ -116,6 +117,7 @@ impl fmt::Display for IoError {
  // just defer to the std implementation for now.
  // we can refine the formatting when more variants are added.
  match *self {
+ #[cfg(feature = "mio")]
  IoError::Mio(ref std_err) => std_err.fmt(f),
  IoError::StdIo(ref std_err) => std_err.fmt(f),
  }