Fix errors for unions with unit target membershape

[drganjoo]

Motivation and Context

Unions that have a unit target member shape do not have an associated data in the generated Rust enum.

Closes Issue: 2546

Description

On the server side, when the union has constrained members, the code generated for the conversion from the Unconstrained type to the Constrained type incorrectly assumed that each Rust enum would have associated data.

rust-server-codegen/src/unconstrained.rs:31:129
  |
  |               crate::unconstrained::some_union_with_unit_unconstrained::SomeUnionWithUnitUnconstrained::Option1(unconstrained) => Self::Option1(
    |                                                                                                                                   -^^^^^^^^^^^^- help: consider using a semicolon here to finish the statement: `;`
    |  _________________________________________________________________________________________________________________________________|
  | |
  | |                 unconstrained
  | |             ),
  | |_____________- call expression requires function
    |
   ::: rust-server-codegen/src/model.rs:152:5
    |
    |       Option1,
    |       ------- `SomeUnionWithUnit::Option1` defined here

The marshaling code for event streams with unit target types incorrectly assumed that the variant would have associated data.

rust-server-codegen/src/event_stream_serde.rs

impl ::aws_smithy_eventstream::frame::MarshallMessage for TestEventMarshaller {
        fn marshal() {
            let payload = match input {
                Self::Input::KeepAlive(inner) => {

On the client side, the event_stream_serde code incorrectly assumes that a union member, which has the @streaming trait applied to it, takes a model::Unit type.

rust-client-codegen/src/event_stream_serde.rs:
    |
    |                     crate::types::TestEvent::KeepAlive(crate::types::Unit::builder().build()),
    |                     ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^---------------------------------------
    |                     |
    |                     call expression requires function
    |
   ::: rust-client-codegen/src/types/_test_event.rs
    |
    |     KeepAlive,
    |     --------- `TestEvent::KeepAlive` defined here

Testing

A unit test has been added that tests the following model:

            $version: "2"
            namespace com.example
            use aws.protocols#restJson1
            use smithy.framework#ValidationException
            
            @restJson1 @title("Test Service") 
            service TestService { 
                version: "0.1", 
                operations: [ 
                    TestOperation
                    TestSimpleUnionWithUnit
                ] 
            }
            
            @http(uri: "/testunit", method: "POST")
            operation TestSimpleUnionWithUnit {
                input := {
                    @required
                    request: SomeUnionWithUnit
                }
                output := {
                    result : SomeUnionWithUnit
                }
                errors: [
                    ValidationException
                ]
            }
            
            @length(min: 13)
            string StringRestricted
            
            union SomeUnionWithUnit {
                Option1: Unit
                Option2: StringRestricted
            }

            @http(uri: "/test", method: "POST")
            operation TestOperation {
                input := { payload: String }
                output := {
                    @httpPayload
                    events: TestEvent
                },
                errors: [ValidationException]
            }
            
            @streaming
            union TestEvent {
                KeepAlive: Unit,
                Response: TestResponseEvent,
            }
            
            structure TestResponseEvent { 
                data: String 
            }            

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• No codegen difference in the AWS SDK
• No codegen difference in the Client Test
• Server Test (ignoring whitespace)
• Server Test Python (ignoring whitespace)
• No codegen difference in the Server Test Typescript

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• No codegen difference in the AWS SDK
• No codegen difference in the Client Test
• Server Test (ignoring whitespace)
• Server Test Python (ignoring whitespace)
• No codegen difference in the Server Test Typescript

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A new generated diff is ready to view.

• No codegen difference in the AWS SDK
• No codegen difference in the Client Test
• Server Test (ignoring whitespace)
• Server Test Python (ignoring whitespace)
• No codegen difference in the Server Test Typescript

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[david-perez]

Not sure why we need the tests below if all we want to check is that the model compiles correctly.

[drganjoo]

So that we can extend the same test to RpcV2Cbor (and possibly other protocols). Since event streams are not covered by the protocol tests, and none of the other tests were failing, I assume we do not have a test that actually checks whether data is being correctly serialized/deserialized. However, having said that, I think it is better to add comprehensive tests that use a client to serialize and then use the server to deserialize it. Currently, these tests directly use the inner data types/methods rather than invoking the server. Will remove these tests for now and we can add one in v2Cbor.

[david-perez]

Closes #2546.

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• No codegen difference in the AWS SDK
• No codegen difference in the Client Test
• Server Test (ignoring whitespace)
• Server Test Python (ignoring whitespace)
• No codegen difference in the Server Test Typescript

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[ysaito1001]

Reviewed primarily those in codegen-core

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• No codegen difference in the AWS SDK
• No codegen difference in the Client Test
• Server Test (ignoring whitespace)
• Server Test Python (ignoring whitespace)
• No codegen difference in the Server Test Typescript

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[github-actions]

A new generated diff is ready to view.

• No codegen difference in the AWS SDK
• No codegen difference in the Client Test
• Server Test (ignoring whitespace)
• Server Test Python (ignoring whitespace)
• No codegen difference in the Server Test Typescript

A new doc preview is ready to view.