From fe30ff311a5105e5765817199f1e9b8d93967ea7 Mon Sep 17 00:00:00 2001
From: Mark Cowlishaw <markcowl@microsoft.com>
Date: Thu, 21 Nov 2024 15:36:38 -0800
Subject: [PATCH] Fix #5001 OkResponse is generated as a model

---
 packages/http-server-csharp/src/service.ts    |  7 ++-
 .../test/generation.test.ts                   | 44 ++++++++++++++++++-
 2 files changed, 49 insertions(+), 2 deletions(-)

diff --git a/packages/http-server-csharp/src/service.ts b/packages/http-server-csharp/src/service.ts
index ad7301414d..a1796912cc 100644
--- a/packages/http-server-csharp/src/service.ts
+++ b/packages/http-server-csharp/src/service.ts
@@ -675,7 +675,8 @@ export async function $onEmit(context: EmitContext<CSharpServiceEmitterOptions>)
       }
 
       for (const response of operation.responses) {
-        this.emitter.emitType(response.type);
+        if (!isEmptyResponseModel(this.emitter.getProgram(), response.type))
+          this.emitter.emitType(response.type);
       }
 
       return builder.reduce();
@@ -1207,6 +1208,10 @@ export async function $onEmit(context: EmitContext<CSharpServiceEmitterOptions>)
     }
   }
 
+  function isEmptyResponseModel(program: Program, model: Type): boolean {
+    if (model.kind !== "Model") return false;
+    return model.properties.size === 1 && isStatusCode(program, [...model.properties.values()][0]);
+  }
   function processNameSpace(program: Program, target: Namespace, service?: Service | undefined) {
     if (!service) service = getService(program, target);
     if (service) {
diff --git a/packages/http-server-csharp/test/generation.test.ts b/packages/http-server-csharp/test/generation.test.ts
index 05da1472ad..aadc474d56 100644
--- a/packages/http-server-csharp/test/generation.test.ts
+++ b/packages/http-server-csharp/test/generation.test.ts
@@ -1,6 +1,6 @@
 import { Program, Type, navigateProgram } from "@typespec/compiler";
 import { BasicTestRunner } from "@typespec/compiler/testing";
-import assert from "assert";
+import assert, { deepStrictEqual } from "assert";
 import { beforeEach, it } from "vitest";
 import { getPropertySource, getSourceModel } from "../src/utils.js";
 import { createCSharpServiceEmitterTestRunner, getStandardService } from "./test-host.js";
@@ -747,6 +747,48 @@ it("Handles void type in operations", async () => {
   );
 });
 
+it("Handles empty body 2xx as void", async () => {
+  await compileAndValidateMultiple(
+    runner,
+    `
+       using TypeSpec.Rest.Resource;
+
+       namespace MyService {
+         model Toy {
+          @key("toyId")
+          id: int64;
+      
+          petId: int64;
+          name: string;
+        }
+
+      @friendlyName("{name}ListResults", Item)
+       model ResponsePage<Item> {
+        items: Item[];
+        nextLink?: string;
+       }
+
+         @post @route("/foo") op foo(...Toy): OkResponse;
+      }
+    `,
+    [
+      [
+        "IMyServiceOperations.cs",
+        ["interface IMyServiceOperations", "Task FooAsync( long id, long petId, string name)"],
+      ],
+      [
+        "MyServiceOperationsControllerBase.cs",
+        [
+          "public abstract partial class MyServiceOperationsControllerBase: ControllerBase",
+          "public virtual async Task<IActionResult> Foo(Toy body)",
+        ],
+      ],
+      ["Toy.cs", ["public partial class Toy"]],
+    ],
+  );
+  deepStrictEqual([...runner.fs.keys()].filter((k) => k.includes("OkResponse.cs")).length, 0);
+});
+
 it("generates appropriate types for literals", async () => {
   await compileAndValidateSingleModel(
     runner,