kdf: impl Display and core::error::Error for Error (#2189)

Minimum viable trait impls for an error type

Author: tarcieri

kdf/src/lib.rs

@@ -8,6 +8,8 @@
 #![forbid(unsafe_code)]
 #![warn(missing_docs, unused_qualifications)]
 
+use core::fmt;
+
 /// Key Derivation Function.
 ///
 /// These functions deterministically produce uniformly random outputs suitable as key material.
@@ -26,5 +28,13 @@ pub trait Pbkdf: Kdf {}
 #[derive(Clone, Copy, Debug, Eq, PartialEq)]
 pub struct Error;
 
+impl fmt::Display for Error {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.write_str("KDF error")
+    }
+}
+
+impl core::error::Error for Error {}
+
 /// Result type with the `kdf` crate's [`Error`].
 pub type Result<T> = core::result::Result<T, Error>;