serial: enforce all traits have the same Error type.

CHANGELOG.md

@@ -13,6 +13,9 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 ### Fixed
 - Fixed blanket impl of `DelayUs` not covering the `delay_ms` method.
 
+### Changed
+- `serial`: traits now enforce all impls on the same struct have the same `Error` type.
+
 ## [v1.0.0-alpha.6] - 2021-11-19
 
 *** This is (also) an alpha release with breaking changes (sorry) ***

src/lib.rs

@@ -143,9 +143,11 @@
 //! // convenience type alias
 //! pub type Serial1 = Serial<USART1>;
 //!
-//! impl hal::serial::nb::Read<u8> for Serial<USART1> {
+//! impl hal::serial::ErrorType for Serial<USART1> {
 //!     type Error = hal::serial::ErrorKind;
+//! }
 //!
+//! impl hal::serial::nb::Read<u8> for Serial<USART1> {
 //!     fn read(&mut self) -> nb::Result<u8, Self::Error> {
 //!         // read the status register
 //!         let isr = self.usart.sr.read();
@@ -166,8 +168,6 @@
 //! }
 //!
 //! impl hal::serial::nb::Write<u8> for Serial<USART1> {
-//!     type Error = hal::serial::ErrorKind;
-//!
 //!     fn write(&mut self, byte: u8) -> nb::Result<(), Self::Error> {
 //!         // Similar to the `read` implementation
 //!         # Ok(())
@@ -387,8 +387,10 @@
 //! #     fn deref_mut(&mut self) -> &mut T { self.0 }
 //! # }
 //! # struct Serial1;
-//! # impl hal::serial::nb::Write<u8> for Serial1 {
+//! # impl hal::serial::ErrorType for Serial1 {
 //! #   type Error = ErrorKind;
+//! # }
+//! # impl hal::serial::nb::Write<u8> for Serial1 {
 //! #   fn write(&mut self, _: u8) -> nb::Result<(), Self::Error> { Err(::nb::Error::WouldBlock) }
 //! #   fn flush(&mut self) -> nb::Result<(), Self::Error> { Err(::nb::Error::WouldBlock) }
 //! # }

src/serial/blocking.rs

@@ -1,10 +1,7 @@
 //! Blocking serial API
 
 /// Write half of a serial interface (blocking variant)
-pub trait Write<Word: Copy = u8> {
-    /// The type of error that can occur when writing
-    type Error: crate::serial::Error;
-
+pub trait Write<Word: Copy = u8>: super::ErrorType {
     /// Writes a slice, blocking until everything has been written
     ///
     /// An implementation can choose to buffer the write, returning `Ok(())`
@@ -20,8 +17,6 @@ pub trait Write<Word: Copy = u8> {
 }
 
 impl<T: Write<Word>, Word: Copy> Write<Word> for &mut T {
-    type Error = T::Error;
-
     fn write(&mut self, buffer: &[Word]) -> Result<(), Self::Error> {
         T::write(self, buffer)
     }

src/serial/mod.rs

@@ -63,3 +63,15 @@ impl core::fmt::Display for ErrorKind {
         }
     }
 }
+
+/// Serial error type trait
+///
+/// This just defines the error type, to be used by the other traits.
+pub trait ErrorType {
+    /// Error type
+    type Error: Error;
+}
+
+impl<T: ErrorType> ErrorType for &mut T {
+    type Error = T::Error;
+}

src/serial/nb.rs

@@ -4,27 +4,19 @@
 ///
 /// Some serial interfaces support different data sizes (8 bits, 9 bits, etc.);
 /// This can be encoded in this trait via the `Word` type parameter.
-pub trait Read<Word: Copy = u8> {
-    /// Read error
-    type Error: crate::serial::Error;
-
+pub trait Read<Word: Copy = u8>: super::ErrorType {
     /// Reads a single word from the serial interface
     fn read(&mut self) -> nb::Result<Word, Self::Error>;
 }
 
 impl<T: Read<Word>, Word: Copy> Read<Word> for &mut T {
-    type Error = T::Error;
-
     fn read(&mut self) -> nb::Result<Word, Self::Error> {
         T::read(self)
     }
 }
 
 /// Write half of a serial interface
-pub trait Write<Word: Copy = u8> {
-    /// Write error
-    type Error: crate::serial::Error;
-
+pub trait Write<Word: Copy = u8>: super::ErrorType {
     /// Writes a single word to the serial interface
     fn write(&mut self, word: Word) -> nb::Result<(), Self::Error>;
 
@@ -33,8 +25,6 @@ pub trait Write<Word: Copy = u8> {
 }
 
 impl<T: Write<Word>, Word: Copy> Write<Word> for &mut T {
-    type Error = T::Error;
-
     fn write(&mut self, word: Word) -> nb::Result<(), Self::Error> {
         T::write(self, word)
     }