feat: support ML host customization (#377)

Author: wooj2

smithy-swift-codegen/src/main/kotlin/software/amazon/smithy/swift/codegen/integration/HttpProtocolTestGenerator.kt

@@ -79,7 +79,11 @@ class HttpProtocolTestGenerator(
 
             cloned.appendMiddleware(operation, RequestTestEndpointResolverMiddleware(ctx.model, ctx.symbolProvider))
             cloned.appendMiddleware(operation, OperationInputUrlPathMiddleware(ctx.model, ctx.symbolProvider, "urlPrefix: urlPrefix"))
-            cloned.appendMiddleware(operation, OperationInputUrlHostMiddleware(ctx.model, ctx.symbolProvider, "host: hostOnly"))
+            val hostMiddlewares = cloned.middlewares(operation, MiddlewareStep.INITIALIZESTEP)
+                .filter { it.name.contains("HostMiddleware") }
+            if (hostMiddlewares.isEmpty()) {
+                cloned.appendMiddleware(operation, OperationInputUrlHostMiddleware(ctx.model, ctx.symbolProvider, "host: hostOnly"))
+            }
         }
         return cloned
     }

smithy-swift-codegen/src/main/kotlin/software/amazon/smithy/swift/codegen/middleware/OperationMiddleware.kt

@@ -7,6 +7,7 @@ interface OperationMiddleware {
     fun appendMiddleware(operation: OperationShape, renderableMiddleware: MiddlewareRenderable)
     fun prependMiddleware(operation: OperationShape, renderableMiddleware: MiddlewareRenderable)
     fun removeMiddleware(operation: OperationShape, step: MiddlewareStep, middlewareName: String)
+    fun middlewares(operation: OperationShape, step: MiddlewareStep): List<MiddlewareRenderable>
 
     fun clone(): OperationMiddleware
 

smithy-swift-codegen/src/main/kotlin/software/amazon/smithy/swift/codegen/middleware/OperationMiddlewareGenerator.kt

@@ -26,6 +26,11 @@ open class OperationMiddlewareGenerator(val mutableHashMap: MutableMap<Operation
         }
     }
 
+    override fun middlewares(operation: OperationShape, step: MiddlewareStep): List<MiddlewareRenderable> {
+        val stack = middlewareMap.getOrPut(operation) { MiddlewareStack() }
+        return resolveStep(stack, step).map { it }
+    }
+
     override fun clone(): OperationMiddleware {
         val copy: MutableMap<OperationShape, MiddlewareStack> = mutableMapOf()
         middlewareMap.forEach { (shape, stack) ->