refactor: use core error

It doesn't require std. This feature is introduced since Rust 1.81.

Author: XuJiandong

src/core/error.rs

@@ -149,9 +149,8 @@ impl<E: fmt::Debug> fmt::Display for DecodeError<E> {
     }
 }
 
-#[cfg(feature = "use_std")]
-impl<E: std::error::Error + 'static> std::error::Error for DecodeError<E> {
-    fn source(&self) -> Option<&(dyn std::error::Error + 'static)> {
+impl<E: core::error::Error + 'static> core::error::Error for DecodeError<E> {
+    fn source(&self) -> Option<&(dyn core::error::Error + 'static)> {
         match self {
             DecodeError::Read(err) => Some(err),
             _ => None
@@ -179,9 +178,8 @@ impl<E: fmt::Debug> fmt::Display for EncodeError<E> {
     }
 }
 
-#[cfg(feature = "use_std")]
-impl<E: std::error::Error + 'static> std::error::Error for EncodeError<E> {
-    fn source(&self) -> Option<&(dyn std::error::Error + 'static)> {
+impl<E: core::error::Error + 'static> core::error::Error for EncodeError<E> {
+    fn source(&self) -> Option<&(dyn core::error::Error + 'static)> {
         match self {
             EncodeError::Write(err) => Some(err),
         }

src/serde/error.rs

@@ -25,44 +25,21 @@ impl<E> From<E> for DecodeError<E> {
 }
 
 #[cfg(feature = "serde1")]
-#[cfg(feature = "use_std")]
-impl<E: std::error::Error + 'static> serde::de::Error for DecodeError<E> {
+impl<E: core::error::Error + 'static> serde::de::Error for DecodeError<E> {
     fn custom<T: fmt::Display>(msg: T) -> Self {
         DecodeError::Custom(msg.to_string().into_boxed_str())
     }
 }
 
-#[cfg(feature = "serde1")]
-#[cfg(not(feature = "use_std"))]
-impl<E: fmt::Debug> serde::de::Error for DecodeError<E> {
-    fn custom<T: fmt::Display>(msg: T) -> Self {
-        #[cfg(not(feature = "use_std"))]
-        use crate::alloc::string::ToString;
-
-        DecodeError::Custom(msg.to_string().into_boxed_str())
-    }
-}
-
 impl<E: fmt::Debug> fmt::Display for DecodeError<E> {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         fmt::Debug::fmt(self, f)
     }
 }
 
 #[cfg(feature = "serde1")]
-#[cfg(not(feature = "use_std"))]
 impl<E: fmt::Debug> serde::ser::StdError for DecodeError<E> {}
 
-#[cfg(feature = "use_std")]
-impl<E: std::error::Error + 'static> std::error::Error for DecodeError<E> {
-    fn source(&self) -> Option<&(dyn std::error::Error + 'static)> {
-        match self {
-            DecodeError::Core(err) => Some(err),
-            _ => None
-        }
-    }
-}
-
 #[derive(Debug)]
 pub enum EncodeError<E> {
     Core(enc::Error<E>),
@@ -86,40 +63,17 @@ impl<E> From<E> for EncodeError<E> {
 }
 
 #[cfg(feature = "serde1")]
-#[cfg(feature = "use_std")]
-impl<E: std::error::Error + 'static> serde::ser::Error for EncodeError<E> {
+impl<E: core::error::Error + 'static> serde::ser::Error for EncodeError<E> {
     fn custom<T: fmt::Display>(msg: T) -> Self {
         EncodeError::Custom(msg.to_string().into_boxed_str())
     }
 }
 
-#[cfg(feature = "serde1")]
-#[cfg(not(feature = "use_std"))]
-impl<E: fmt::Debug> serde::ser::Error for EncodeError<E> {
-    fn custom<T: fmt::Display>(msg: T) -> Self {
-        #[cfg(not(feature = "use_std"))]
-        use crate::alloc::string::ToString;
-
-        EncodeError::Custom(msg.to_string().into_boxed_str())
-    }
-}
-
 impl<E: fmt::Debug> fmt::Display for EncodeError<E> {
     fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
         fmt::Debug::fmt(self, f)
     }
 }
 
 #[cfg(feature = "serde1")]
-#[cfg(not(feature = "use_std"))]
 impl<E: fmt::Debug> serde::ser::StdError for EncodeError<E> {}
-
-#[cfg(feature = "use_std")]
-impl<E: std::error::Error + 'static> std::error::Error for EncodeError<E> {
-    fn source(&self) -> Option<&(dyn std::error::Error + 'static)> {
-        match self {
-            EncodeError::Core(err) => Some(err),
-            _ => None
-        }
-    }
-}