update CHANGELOG

Signed-off-by: Daniele Ahmed <[email protected]>

CHANGELOG.next.toml

@@ -24,25 +24,121 @@ meta = { "breaking" = true, "tada" = false, "bug" = false }
 author = "82marbag"
 
 [[aws-sdk-rust]]
-message = "Generate event stream specific error types"
+message = """
+The type of streaming unions that contain errors is generated without those errors.
+Errors in a streaming union `Union` are generated as members of the type `UnionError`.
+Taking Transcribe as an example, the `AudioStream` streaming union generates, in the client, both the `AudioStream` type:
+```rust
+pub enum AudioStream {
+    AudioEvent(crate::model::AudioEvent),
+    Unknown,
+}
+```
+and its error type,
+```rust
+pub struct AudioStreamError {
+    /// Kind of error that occurred.
+    pub kind: AudioStreamErrorKind,
+    /// Additional metadata about the error, including error code, message, and request ID.
+    pub(crate) meta: aws_smithy_types::Error,
+}
+```
+`AudioStreamErrorKind` contains all error variants for the union.
+Before, the generated code looked as:
+```rust
+pub enum AudioStream {
+    AudioEvent(crate::model::AudioEvent),
+    ... all error variants,
+    Unknown,
+}
+```
+"""
 references = ["smithy-rs#1157"]
 meta = { "breaking" = true, "tada" = false, "bug" = false }
 author = "82marbag"
 
 [[aws-sdk-rust]]
-message = "EventStreamSender and Receiver use event stream specific error types"
+message = """
+`aws_smithy_http::event_stream::EventStreamSender` and `aws_smithy_http::event_stream::Receiver` are now generic over `<T, E>`,
+where `T` is a streaming union and `E` the union's errors.
+This means that event stream errors are now sent as `Err` of the union's error type.
+With this example model:
+```smithy
+@streaming union Event {
+    throttlingError: ThrottlingError
+}
+@error("client") structure ThrottlingError {}
+```
+Before:
+```rust
+stream! { yield Ok(Event::ThrottlingError ...) }
+```
+After:
+```rust
+stream! { yield Err(EventError::ThrottlingError ...) }
+```
+An example from the SDK is in [transcribe streaming](https://github.com/awslabs/smithy-rs/blob/4f51dd450ea3234a7faf481c6025597f22f03805/aws/sdk/integration-tests/transcribestreaming/tests/test.rs#L80).
+"""
 references = ["smithy-rs#1157"]
 meta = { "breaking" = true, "tada" = false, "bug" = false }
 author = "82marbag"
 
 [[smithy-rs]]
-message = "Generate event stream specific error types"
+message = """
+The type of streaming unions that contain errors is generated without those errors.
+Errors in a streaming union `Union` are generated as members of the type `UnionError`.
+Taking Transcribe as an example, the `AudioStream` streaming union generates, in the client, both the `AudioStream` type:
+```rust
+pub enum AudioStream {
+    AudioEvent(crate::model::AudioEvent),
+    Unknown,
+}
+```
+and its error type,
+```rust
+pub struct AudioStreamError {
+    /// Kind of error that occurred.
+    pub kind: AudioStreamErrorKind,
+    /// Additional metadata about the error, including error code, message, and request ID.
+    pub(crate) meta: aws_smithy_types::Error,
+}
+```
+`AudioStreamErrorKind` contains all error variants for the union.
+Before, the generated code looked as:
+```rust
+pub enum AudioStream {
+    AudioEvent(crate::model::AudioEvent),
+    ... all error variants,
+    Unknown,
+}
+```
+"""
 references = ["smithy-rs#1157"]
 meta = { "breaking" = true, "tada" = false, "bug" = false }
 author = "82marbag"
 
 [[smithy-rs]]
-message = "EventStreamSender and Receiver use event stream specific error types"
+message = """
+`aws_smithy_http::event_stream::EventStreamSender` and `aws_smithy_http::event_stream::Receiver` are now generic over `<T, E>`,
+where `T` is a streaming union and `E` the union's errors.
+This means that event stream errors are now sent as `Err` of the union's error type.
+With this example model:
+```smithy
+@streaming union Event {
+    throttlingError: ThrottlingError
+}
+@error("client") structure ThrottlingError {}
+```
+Before:
+```rust
+stream! { yield Ok(Event::ThrottlingError ...) }
+```
+After:
+```rust
+stream! { yield Err(EventError::ThrottlingError ...) }
+```
+An example from the SDK is in [transcribe streaming](https://github.com/awslabs/smithy-rs/blob/4f51dd450ea3234a7faf481c6025597f22f03805/aws/sdk/integration-tests/transcribestreaming/tests/test.rs#L80).
+"""
 references = ["smithy-rs#1157"]
 meta = { "breaking" = true, "tada" = false, "bug" = false }
 author = "82marbag"