Improve io and error

Author: Pratyush

std/src/error.rs

@@ -1,27 +1,54 @@
 use crate::boxed::Box;
+use crate::fmt::{self, Debug, Display};
+use crate::string::String;
 
-#[cfg(feature = "std")]
-pub use std::error::Error;
-
-#[cfg(not(feature = "std"))]
 pub trait Error: core::fmt::Debug + core::fmt::Display {
     fn source(&self) -> Option<&(dyn Error + 'static)> {
         None
     }
 }
 
-#[cfg(not(feature = "std"))]
 impl<'a, E: Error + 'a> From<E> for Box<dyn Error + 'a> {
     fn from(err: E) -> Self {
         Box::new(err)
     }
 }
 
-#[cfg(not(feature = "std"))]
+impl<'a, E: Error + Send + Sync + 'a> From<E> for Box<dyn Error + Send + Sync + 'a> {
+    fn from(err: E) -> Box<dyn Error + Send + Sync + 'a> {
+        Box::new(err)
+    }
+}
+
 impl<T: Error> Error for Box<T> {}
 
-#[cfg(not(feature = "std"))]
-impl Error for crate::string::String {}
+impl From<String> for Box<dyn Error + Send + Sync> {
+    #[inline]
+    fn from(err: String) -> Box<dyn Error + Send + Sync> {
+        struct StringError(String);
+
+        impl Error for StringError {}
+
+        impl Display for StringError {
+            fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+                Display::fmt(&self.0, f)
+            }
+        }
 
-#[cfg(not(feature = "std"))]
-impl Error for crate::io::Error {}
+        // Purposefully skip printing "StringError(..)"
+        impl Debug for StringError {
+            fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+                Debug::fmt(&self.0, f)
+            }
+        }
+
+        Box::new(StringError(err))
+    }
+}
+
+impl<'a> From<&'a str> for Box<dyn Error + Send + Sync> {
+    #[inline]
+    fn from(err: &'a str) -> Box<dyn Error + Send + Sync> {
+        From::from(String::from(err))
+    }
+}