operationShapesThatMustHaveValidationException does not account for event streaming members.

[drganjoo]

When an operation's input includes an event streaming member, the builder for the operation input or output can raise a ConstraintViolation if build_enforcing_all_constraints is called and the event streaming member field has not been set.

The From implementation that converts ConstraintViolation to RequestRejection references ValidationException. However, if the user has not added ValidationException to the errors list, a build-time error is not generated to prompt the user to include ValidationException.

The operationShapesThatMustHaveValidationException method should raise an error in this case.

Here is a sample model:

service ConstrainedService {
    operations: [EventStreamsOperation]
}

structure EventStreamsOperationInputOutput {
    @httpPayload
    events: Event,
}

@http(uri: "/event-streams-operation", method: "POST")
operation EventStreamsOperation {
    input: EventStreamsOperationInputOutput,
    output: EventStreamsOperationInputOutput,
}

@streaming
union Event {
    regularMessage: EventStreamRegularMessage,
    errorMessage: EventStreamErrorMessage,
}

structure EventStreamRegularMessage {
    messageContent: String
}

@error("server")
structure EventStreamErrorMessage {
    messageContent: String
}

In the operation input builder, build_enforcing_all_constraints returns a ConstraintViolation if constraints are not met:

        fn build_enforcing_all_constraints(
            self,
        ) -> Result<crate::input::EventStreamsOperationInput, ConstraintViolation> {
            Ok(
                crate::input::EventStreamsOperationInput {
                    events: self
                        .events
                        .ok_or(ConstraintViolation::MissingEvents)?,
                },
            )
        }

The From implementation for converting ConstraintViolation to RequestRejection uses crate::error::ValidationException:

    impl ::std::convert::From<ConstraintViolation>
        for ::aws_smithy_http_server::protocol::rpc_v2_cbor::rejection::RequestRejection
    {
        fn from(constraint_violation: ConstraintViolation) -> Self {
            let first_validation_exception_field =
                constraint_violation.as_validation_exception_field("".to_owned());
            let validation_exception = crate::error::ValidationException {

The generated Rust code errors out with:

error[E0412]: cannot find type `ValidationExceptionField` in module `crate::model`
  --> src/input.rs:78:28
   |
78 |         ) -> crate::model::ValidationExceptionField {
   |                            ^^^^^^^^^^^^^^^^^^^^^^^^ not found in `crate::model`

[david-perez]

You must always have ValidationException in an event streaming operation because the event (the member on the input structure that targets a Smithy union/ Rust enum) is always required.