Render only shape name in server error responses (#2866)

This essentially reverts the behavior introduced in #1982.

The rationale for that change:

> [...] since some existing clients rely on it to deserialize the error
shape
> and fail if only the shape name is present

no longer holds. Since serializing only the shape name is a SHOULD in
the spec, it's best that we honor it.

## Checklist
<!--- If a checkbox below is not applicable, then please DELETE it
rather than leaving it unchecked -->
- [x] I have updated `CHANGELOG.next.toml` if I made changes to the
smithy-rs codegen or runtime crates

----

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copy, and redistribute this contribution, under the terms of your
choice._

CHANGELOG.next.toml

@@ -664,3 +664,25 @@ message = "The `alb_health_check` module has been moved out of the `plugin` modu
 references = ["smithy-rs#2865"]
 meta = { "breaking" = true, "tada" = false, "bug" = false, "target" = "server" }
 author = "david-perez"
+
+[[smithy-rs]]
+message = """
+[RestJson1](https://awslabs.github.io/smithy/2.0/aws/protocols/aws-restjson1-protocol.html#operation-error-serialization) server SDKs now serialize only the [shape name](https://smithy.io/2.0/spec/model.html#shape-id) in operation error responses. Previously (from versions 0.52.0 to 0.55.4), the full shape ID was rendered.
+Example server error response by a smithy-rs server version 0.52.0 until 0.55.4:
+```
+HTTP/1.1 400 Bad Request
+content-type: application/json
+x-amzn-errortype: com.example.service#InvalidRequestException
+...
+```
+Example server error response now:
+```
+HTTP/1.1 400 Bad Request
+content-type: application/json
+x-amzn-errortype: InvalidRequestException
+...
+```
+"""
+references = ["smithy-rs#2866"]
+meta = { "breaking" = false, "tada" = false, "bug" = false, "target" = "server" }
+author = "david-perez"

codegen-core/common-test-models/rest-json-extras.smithy

@@ -81,16 +81,12 @@ service RestJsonExtras {
         appliesTo: "client",
     },
     {
-        documentation: """
-            Upper case error modeled lower case.
-            Servers render the full shape ID (including namespace), since some
-            existing clients rely on it to deserialize the error shape and fail
-            if only the shape name is present.""",
+        documentation: "Upper case error modeled lower case.",
         id: "ServiceLevelErrorServer",
         protocol: "aws.protocols#restJson1",
         code: 500,
         body: "{}",
-        headers: { "X-Amzn-Errortype": "aws.protocoltests.restjson#ExtraError" },
+        headers: { "X-Amzn-Errortype": "ExtraError" },
         params: {},
         appliesTo: "server",
     }

codegen-core/src/main/kotlin/software/amazon/smithy/rust/codegen/core/smithy/protocols/RestJson.kt

@@ -80,14 +80,19 @@ open class RestJson(val codegenContext: CodegenContext) : Protocol {
      * RestJson1 implementations can denote errors in responses in several ways.
      * New server-side protocol implementations MUST use a header field named `X-Amzn-Errortype`.
      *
-     * Note that the spec says that implementations SHOULD strip the error shape ID's namespace.
-     * However, our server implementation renders the full shape ID (including namespace), since some
-     * existing clients rely on it to deserialize the error shape and fail if only the shape name is present.
-     * This is compliant with the spec, see https://github.com/awslabs/smithy/pull/1493.
-     * See https://github.com/awslabs/smithy/issues/1494 too.
+     * Note that the spec says that implementations SHOULD strip the error shape ID's namespace
+     * (see https://smithy.io/2.0/aws/protocols/aws-restjson1-protocol.html#operation-error-serialization):
+     *
+     * > The value of this component SHOULD contain only the shape name of the error's Shape ID.
+     *
+     * But it's a SHOULD; we could strip the namespace if we wanted to. In fact, we did so in smithy-rs versions
+     * 0.52.0 to 0.55.4; see:
+     * - https://github.com/awslabs/smithy-rs/pull/1982
+     * - https://github.com/awslabs/smithy/pull/1493
+     * - https://github.com/awslabs/smithy/issues/1494
      */
     override fun additionalErrorResponseHeaders(errorShape: StructureShape): List<Pair<String, String>> =
-        listOf("x-amzn-errortype" to errorShape.id.toString())
+        listOf("x-amzn-errortype" to errorShape.id.name)
 
     override fun structuredDataParser(): StructuredDataParserGenerator =
         JsonParserGenerator(codegenContext, httpBindingResolver, ::restJsonFieldName)

codegen-server/src/main/kotlin/software/amazon/smithy/rust/codegen/server/smithy/generators/protocol/ServerProtocolTestGenerator.kt

@@ -921,15 +921,6 @@ class ServerProtocolTestGenerator(
                 ).asObjectNode().get(),
             ).build()
 
-        private fun fixRestJsonInvalidGreetingError(testCase: HttpResponseTestCase): HttpResponseTestCase =
-            testCase.toBuilder().putHeader("X-Amzn-Errortype", "aws.protocoltests.restjson#InvalidGreeting").build()
-
-        private fun fixRestJsonEmptyComplexErrorWithNoMessage(testCase: HttpResponseTestCase): HttpResponseTestCase =
-            testCase.toBuilder().putHeader("X-Amzn-Errortype", "aws.protocoltests.restjson#ComplexError").build()
-
-        private fun fixRestJsonComplexErrorWithNoMessage(testCase: HttpResponseTestCase): HttpResponseTestCase =
-            testCase.toBuilder().putHeader("X-Amzn-Errortype", "aws.protocoltests.restjson#ComplexError").build()
-
         // TODO(https://github.com/awslabs/smithy/issues/1506)
         private fun fixRestJsonMalformedPatternReDOSString(testCase: HttpMalformedRequestTestCase): HttpMalformedRequestTestCase {
             val brokenResponse = testCase.response
@@ -962,12 +953,7 @@ class ServerProtocolTestGenerator(
         )
 
         private val BrokenResponseTests: Map<Pair<String, String>, KFunction1<HttpResponseTestCase, HttpResponseTestCase>> =
-            // TODO(https://github.com/awslabs/smithy/issues/1494)
-            mapOf(
-                Pair(RestJson, "RestJsonInvalidGreetingError") to ::fixRestJsonInvalidGreetingError,
-                Pair(RestJson, "RestJsonEmptyComplexErrorWithNoMessage") to ::fixRestJsonEmptyComplexErrorWithNoMessage,
-                Pair(RestJson, "RestJsonComplexErrorWithNoMessage") to ::fixRestJsonComplexErrorWithNoMessage,
-            )
+            mapOf()
 
         private val BrokenMalformedRequestTests: Map<Pair<String, String>, KFunction1<HttpMalformedRequestTestCase, HttpMalformedRequestTestCase>> =
             // TODO(https://github.com/awslabs/smithy/issues/1506)

codegen-server/src/main/kotlin/software/amazon/smithy/rust/codegen/server/smithy/protocols/ServerAwsJson.kt

@@ -68,6 +68,14 @@ class ServerAwsJsonFactory(
 /**
  * AwsJson requires errors to be serialized in server responses with an additional `__type` field. This
  * customization writes the right field depending on the version of the AwsJson protocol.
+ *
+ * From the specs:
+ * - https://smithy.io/2.0/aws/protocols/aws-json-1_0-protocol.html#operation-error-serialization
+ * - https://smithy.io/2.0/aws/protocols/aws-json-1_1-protocol.html#operation-error-serialization
+ *
+ * > Error responses in the <awsJson1_x> protocol are serialized identically to standard responses with one additional
+ * > component to distinguish which error is contained. New server-side protocol implementations SHOULD use a body
+ * > field named __type
  */
 class ServerAwsJsonError(private val awsJsonVersion: AwsJsonVersion) : JsonSerializerCustomization() {
     override fun section(section: JsonSerializerSection): Writable = when (section) {