Restore SmokeTestsDecoratorTest (#3811)

## Motivation and Context
Restores `SmokeTestsDecoratorTest` that was temporarily removed in
#3808.

## Description
The said test was temporarily removed because `SmokeTestsDecorator` is
included in the [predefined
decorators](https://github.com/smithy-lang/smithy-rs/blob/b38ccb969e09ae0856c235fcb496b3f3faf41c87/aws/sdk-codegen/src/main/kotlin/software/amazon/smithy/rustsdk/AwsCodegenDecorator.kt#L35)
and pulls-in the `aws-config` crate for code generation. The issue was
conflicts between the runtime crates used by `aws-config` (located in
the `aws/sdk/build` directory) and those brought-in by that predefined
decorators used by `awsSdkIntegrationTest` (located in the
`rust-runtime` and `aws/rust-runtime` directories). This PR addresses
these conflicts and restores the test functionality.

Given the challenges, the code changes are centered around the following
ideas:
- Focus solely on testing the core class, `SmokeTestsInstantiator`. By
doing this, we avoid running `SmokeTestsDecorator`, which would
otherwise pull in the `aws-config` crate.
- Initializing a config builder in smoke tests needs to be parameterized
depending on the environment; in production we use
`aws_config::load_defaults` and in testing we avoid including
`aws-config` by using a default-constructed config builder, which is
sufficient for compile-only tests.
- The generated smoke tests in `SmokeTestsDecoratorTest` require minimal
runtime crates for compilation. We need the `CodegenVisitor` but with a
different set of codegen decorators. Prior to this PR,
`awsSdkIntegrationTest` used
[RustClientCodegenPlugin](https://github.com/smithy-lang/smithy-rs/blob/b38ccb969e09ae0856c235fcb496b3f3faf41c87/codegen-client/src/main/kotlin/software/amazon/smithy/rust/codegen/client/smithy/RustClientCodegenPlugin.kt#L46)
that in turn loaded [predefined
decorators](https://github.com/smithy-lang/smithy-rs/blob/b38ccb969e09ae0856c235fcb496b3f3faf41c87/aws/sdk-codegen/src/main/kotlin/software/amazon/smithy/rustsdk/AwsCodegenDecorator.kt#L35)
on the classpath, which included `SmokeTestsDecorator`. In this PR, we
work around this by defining a minimal set of codegen decorators and
making them pluggable through `awsSdkIntegrationTest`.

## Testing
Tests in CI

----

_By submitting this pull request, I confirm that you can use, modify,
copy, and redistribute this contribution, under the terms of your
choice._

aws/sdk-codegen/src/main/kotlin/software/amazon/smithy/rustsdk/SmokeTestsDecorator.kt

@@ -18,10 +18,13 @@ import software.amazon.smithy.rust.codegen.core.rustlang.Attribute
 import software.amazon.smithy.rust.codegen.core.rustlang.Attribute.Companion.cfg
 import software.amazon.smithy.rust.codegen.core.rustlang.AttributeKind
 import software.amazon.smithy.rust.codegen.core.rustlang.RustWriter
+import software.amazon.smithy.rust.codegen.core.rustlang.Writable
 import software.amazon.smithy.rust.codegen.core.rustlang.containerDocs
 import software.amazon.smithy.rust.codegen.core.rustlang.docs
 import software.amazon.smithy.rust.codegen.core.rustlang.rust
 import software.amazon.smithy.rust.codegen.core.rustlang.rustBlock
+import software.amazon.smithy.rust.codegen.core.rustlang.rustTemplate
+import software.amazon.smithy.rust.codegen.core.rustlang.writable
 import software.amazon.smithy.rust.codegen.core.smithy.CodegenContext
 import software.amazon.smithy.rust.codegen.core.smithy.PublicImportSymbolProvider
 import software.amazon.smithy.rust.codegen.core.smithy.RustCrate
@@ -67,66 +70,83 @@ class SmokeTestsDecorator : ClientCodegenDecorator {
         rustCrate: RustCrate,
     ) {
         // Get all operations with smoke tests
-        val smokeTestedOperations =
-            codegenContext.model.getOperationShapesWithTrait(SmokeTestsTrait::class.java).toList()
+        val smokeTestedOperations = operationToTestCases(codegenContext.model)
         val supportedTests =
-            smokeTestedOperations.map { operationShape ->
+            smokeTestedOperations.map { (operationShape, testCases) ->
                 // filter out unsupported smoke tests, logging a warning for each one, and sort the remaining tests by
                 // case ID. This ensures deterministic rendering, meaning the test methods are always rendered in a
                 // consistent order.
-                val testCases =
-                    operationShape.expectTrait<SmokeTestsTrait>().testCases.filter { smokeTestCase ->
-                        isSmokeTestSupported(smokeTestCase)
-                    }.sortedBy { smokeTestCase -> smokeTestCase.id }
+                testCases.filter { smokeTestCase ->
+                    isSmokeTestSupported(smokeTestCase)
+                }.sortedBy { smokeTestCase -> smokeTestCase.id }
 
                 operationShape to testCases
             }
                 // filter out operations with no supported smoke tests
                 .filter { (_, testCases) -> testCases.isNotEmpty() }
                 // Similar to sorting test cases above, sort operations by name to ensure consistent ordering.
                 .sortedBy { (operationShape, _) -> operationShape.id.name }
+
         // Return if there are no supported smoke tests across all operations
         if (supportedTests.isEmpty()) return
 
         rustCrate.integrationTest("smoketests") {
-            // Don't run the tests in this module unless `RUSTFLAGS="--cfg smoketests"` is passed.
-            Attribute(cfg("smoketests")).render(this, AttributeKind.Inner)
-
-            containerDocs(
-                """
-                The tests in this module run against live AWS services. As such,
-                they are disabled by default. To enable them, run the tests with
-
-                ```sh
-                RUSTFLAGS="--cfg smoketests" cargo test.
-                ```""",
-            )
-
-            val model = codegenContext.model
-            val moduleUseName = codegenContext.moduleUseName()
-            rust("use $moduleUseName::{ Client, config };")
+            renderPrologue(codegenContext.moduleUseName(), this)
 
             for ((operationShape, testCases) in supportedTests) {
-                val operationName = operationShape.id.name.toSnakeCase()
-                val operationInput = operationShape.inputShape(model)
-
-                docs("Smoke tests for the `$operationName` operation")
-
+                docs("Smoke tests for the `${operationShape.id.name.toSnakeCase()}` operation")
+                val instantiator =
+                    SmokeTestsInstantiator(
+                        codegenContext, operationShape,
+                        configBuilderInitializer = { ->
+                            writable {
+                                rustTemplate(
+                                    """
+                                    let config = #{awsConfig}::load_defaults(config::BehaviorVersion::latest()).await;
+                                    let conf = config::Config::from(&config).to_builder()
+                                    """,
+                                    "awsConfig" to AwsCargoDependency.awsConfig(codegenContext.runtimeConfig).toType(),
+                                )
+                            }
+                        },
+                    )
                 for (testCase in testCases) {
                     Attribute.TokioTest.render(this)
                     this.rustBlock("async fn test_${testCase.id.toSnakeCase()}()") {
-                        val instantiator = SmokeTestsInstantiator(codegenContext)
-                        instantiator.renderConf(this, testCase)
-                        rust("let client = Client::from_conf(conf);")
-                        instantiator.renderInput(this, operationShape, operationInput, testCase.params)
-                        instantiator.renderExpectation(this, model, testCase.expectation)
+                        instantiator.render(this, testCase)
                     }
                 }
             }
         }
     }
 }
 
+fun renderPrologue(
+    moduleUseName: String,
+    writer: RustWriter,
+) = writer.apply {
+    // Don't run the tests in this module unless `RUSTFLAGS="--cfg smoketests"` is passed.
+    Attribute(cfg("smoketests")).render(this, AttributeKind.Inner)
+
+    containerDocs(
+        """
+        The tests in this module run against live AWS services. As such,
+        they are disabled by default. To enable them, run the tests with
+
+        ```sh
+        RUSTFLAGS="--cfg smoketests" cargo test.
+        ```
+        """,
+    )
+
+    rust("use $moduleUseName::{Client, config};")
+}
+
+fun operationToTestCases(model: Model) =
+    model.getOperationShapesWithTrait(SmokeTestsTrait::class.java).toList().map { operationShape ->
+        operationShape to operationShape.expectTrait<SmokeTestsTrait>().testCases
+    }
+
 class SmokeTestsBuilderKindBehavior(val codegenContext: CodegenContext) : Instantiator.BuilderKindBehavior {
     override fun hasFallibleBuilder(shape: StructureShape): Boolean =
         BuilderGenerator.hasFallibleBuilder(shape, codegenContext.symbolProvider)
@@ -136,89 +156,99 @@ class SmokeTestsBuilderKindBehavior(val codegenContext: CodegenContext) : Instan
     override fun doesSetterTakeInOption(memberShape: MemberShape): Boolean = true
 }
 
-class SmokeTestsInstantiator(private val codegenContext: ClientCodegenContext) : Instantiator(
-    PublicImportSymbolProvider(codegenContext.symbolProvider, codegenContext.moduleUseName()),
-    codegenContext.model,
-    codegenContext.runtimeConfig,
-    SmokeTestsBuilderKindBehavior(codegenContext),
-) {
-    fun renderConf(
+class SmokeTestsInstantiator(
+    codegenContext: ClientCodegenContext, private val operationShape: OperationShape,
+    private val configBuilderInitializer: () -> Writable,
+) : Instantiator(
+        PublicImportSymbolProvider(codegenContext.symbolProvider, codegenContext.moduleUseName()),
+        codegenContext.model,
+        codegenContext.runtimeConfig,
+        SmokeTestsBuilderKindBehavior(codegenContext),
+    ) {
+    private val model = codegenContext.model
+    private val symbolProvider = codegenContext.symbolProvider
+
+    fun render(
         writer: RustWriter,
         testCase: SmokeTestCase,
-    ) {
-        writer.rust(
-            "let config = #{T}::load_defaults(config::BehaviorVersion::latest()).await;",
-            AwsCargoDependency.awsConfig(codegenContext.runtimeConfig).toType(),
-        )
-        writer.rust("let conf = config::Config::from(&config).to_builder()")
-        writer.indent()
+    ) = writer.apply {
+        renderConf(this, testCase)
+        rust("let client = Client::from_conf(conf);")
+        renderInput(this, testCase.params)
+        renderExpectation(this, testCase.expectation)
+    }
+
+    private fun renderConf(
+        writer: RustWriter,
+        testCase: SmokeTestCase,
+    ) = writer.apply {
+        rustTemplate("#{config_builder_initializer}", "config_builder_initializer" to configBuilderInitializer())
+        indent()
 
         // TODO(https://github.com/smithy-lang/smithy-rs/issues/3776) Once Account ID routing is supported,
         //  reflect the config setting here, especially to disable it if needed, as it is enabled by default in
         //  `AwsVendorParams`.
 
         val vendorParams = AwsSmokeTestModel.getAwsVendorParams(testCase)
         vendorParams.orNull()?.let { params ->
-            writer.rust(".region(config::Region::new(${params.region.dq()}))")
-            writer.rust(".use_dual_stack(${params.useDualstack()})")
-            writer.rust(".use_fips(${params.useFips()})")
-            params.uri.orNull()?.let { writer.rust(".endpoint_url($it)") }
+            rust(".region(config::Region::new(${params.region.dq()}))")
+            rust(".use_dual_stack(${params.useDualstack()})")
+            rust(".use_fips(${params.useFips()})")
+            params.uri.orNull()?.let { rust(".endpoint_url($it)") }
         }
 
         val s3VendorParams = AwsSmokeTestModel.getS3VendorParams(testCase)
         s3VendorParams.orNull()?.let { params ->
-            writer.rust(".accelerate_(${params.useAccelerate()})")
-            writer.rust(".force_path_style_(${params.forcePathStyle()})")
-            writer.rust(".use_arn_region(${params.useArnRegion()})")
-            writer.rust(".disable_multi_region_access_points(${params.useMultiRegionAccessPoints().not()})")
+            rust(".accelerate_(${params.useAccelerate()})")
+            rust(".force_path_style_(${params.forcePathStyle()})")
+            rust(".use_arn_region(${params.useArnRegion()})")
+            rust(".disable_multi_region_access_points(${params.useMultiRegionAccessPoints().not()})")
         }
 
-        writer.rust(".build();")
-        writer.dedent()
+        rust(".build();")
+        dedent()
     }
 
-    fun renderInput(
+    private fun renderInput(
         writer: RustWriter,
-        operationShape: OperationShape,
-        inputShape: StructureShape,
         data: Optional<ObjectNode>,
         headers: Map<String, String> = mapOf(),
         ctx: Ctx = Ctx(),
-    ) {
+    ) = writer.apply {
         val operationBuilderName =
-            FluentClientGenerator.clientOperationFnName(operationShape, codegenContext.symbolProvider)
+            FluentClientGenerator.clientOperationFnName(operationShape, symbolProvider)
+        val inputShape = operationShape.inputShape(model)
 
-        writer.rust("let res = client.$operationBuilderName()")
-        writer.indent()
+        rust("let res = client.$operationBuilderName()")
+        indent()
         data.orNull()?.let {
             renderStructureMembers(writer, inputShape, it, headers, ctx)
         }
-        writer.rust(".send().await;")
-        writer.dedent()
+        rust(".send().await;")
+        dedent()
     }
 
-    fun renderExpectation(
+    private fun renderExpectation(
         writer: RustWriter,
-        model: Model,
         expectation: Expectation,
-    ) {
+    ) = writer.apply {
         if (expectation.isSuccess) {
-            writer.rust("""res.expect("request should succeed");""")
+            rust("""res.expect("request should succeed");""")
         } else if (expectation.isFailure) {
             val expectedErrShape = expectation.failure.orNull()?.errorId?.orNull()
             println(expectedErrShape)
             if (expectedErrShape != null) {
                 val failureShape = model.expectShape(expectedErrShape)
-                val errName = codegenContext.symbolProvider.toSymbol(failureShape).name.toSnakeCase()
-                writer.rust(
+                val errName = symbolProvider.toSymbol(failureShape).name.toSnakeCase()
+                rust(
                     """
                     let err = res.expect_err("request should fail");
                     let err = err.into_service_error();
                     assert!(err.is_$errName())
                     """,
                 )
             } else {
-                writer.rust("""res.expect_err("request should fail");""")
+                rust("""res.expect_err("request should fail");""")
             }
         }
     }