refactor: replace failure

- failure is deprecated
- thiserror for deriving Error impl
- anyhow for highlevel error handling

src/smtp/mod.rs

@@ -16,35 +16,29 @@ use crate::oauth2::*;
 /// SMTP write and read timeout in seconds.
 const SMTP_TIMEOUT: u64 = 30;
 
-#[derive(Debug, Fail)]
+#[derive(Debug, thiserror::Error)]
 pub enum Error {
-    #[fail(display = "Bad parameters")]
+    #[error("Bad parameters")]
     BadParameters,
 
-    #[fail(display = "Invalid login address {}: {}", address, error)]
+    #[error("Invalid login address {address}: {error}")]
     InvalidLoginAddress {
         address: String,
-        #[cause]
+        #[source]
         error: error::Error,
     },
 
-    #[fail(display = "SMTP failed to connect: {:?}", _0)]
-    ConnectionFailure(#[cause] smtp::error::Error),
+    #[error("SMTP: failed to connect: {0:?}")]
+    ConnectionFailure(#[source] smtp::error::Error),
 
-    #[fail(display = "SMTP: failed to setup connection {:?}", _0)]
-    ConnectionSetupFailure(#[cause] smtp::error::Error),
+    #[error("SMTP: failed to setup connection {0:?}")]
+    ConnectionSetupFailure(#[source] smtp::error::Error),
 
-    #[fail(display = "SMTP: oauth2 error {:?}", _0)]
+    #[error("SMTP: oauth2 error {address}")]
     Oauth2Error { address: String },
 
-    #[fail(display = "TLS error")]
-    Tls(#[cause] async_native_tls::Error),
-}
-
-impl From<async_native_tls::Error> for Error {
-    fn from(err: async_native_tls::Error) -> Error {
-        Error::Tls(err)
-    }
+    #[error("TLS error")]
+    Tls(#[from] async_native_tls::Error),
 }
 
 pub type Result<T> = std::result::Result<T, Error>;