Implement std::error::Error for our custom errors

For allowing a more ergonomic use and better integration on the
ecosystem, this adds the `std::error::Error` `impl` for our custom
errors.

We intent to drop this hand made code once `derive_more` finishes the
addition of the Error derive support[1]. Until that is available, we
need to live with that.

1. https://github.com/JelteF/derive_more/issues/92

Signed-off-by: Otavio Salvador <otavio@ossystems.com.br>

awc/CHANGES.md

@@ -1,5 +1,13 @@
 # Changes
 
+## [Unreleased]
+
+### Changed
+
+* Implement `std::error::Error` for our custom errors [#1422]
+
+[#1422]: https://github.com/actix/actix-web/pull/1422
+
 ## [2.0.0-alpha.1] - 2020-03-11
 
 * Update `actix-http` dependency to 2.0.0-alpha.2

awc/src/error.rs

@@ -42,6 +42,8 @@ pub enum WsClientError {
     SendRequest(SendRequestError),
 }
 
+impl std::error::Error for WsClientError {}
+
 impl From<InvalidUrl> for WsClientError {
     fn from(err: InvalidUrl) -> Self {
         WsClientError::SendRequest(err.into())
@@ -68,5 +70,7 @@ pub enum JsonPayloadError {
     Payload(PayloadError),
 }
 
+impl std::error::Error for JsonPayloadError {}
+
 /// Return `InternalServerError` for `JsonPayloadError`
 impl ResponseError for JsonPayloadError {}