From a0ec8be311daef0285d8485e315bbb49a9370f44 Mon Sep 17 00:00:00 2001
From: Artem Zakharchenko <kettanaito@gmail.com>
Date: Sat, 4 Nov 2023 16:21:08 +0100
Subject: [PATCH] fix: correctly check "undefined" as response body type
 (#1824)

---
 src/core/handlers/RequestHandler.ts                   |  4 ++--
 test/typings/regressions/response-body-type.test-d.ts | 10 ++++++++++
 2 files changed, 12 insertions(+), 2 deletions(-)
 create mode 100644 test/typings/regressions/response-body-type.test-d.ts

diff --git a/src/core/handlers/RequestHandler.ts b/src/core/handlers/RequestHandler.ts
index 8f45a6e41..da25a7662 100644
--- a/src/core/handlers/RequestHandler.ts
+++ b/src/core/handlers/RequestHandler.ts
@@ -30,7 +30,7 @@ export interface RequestHandlerInternalInfo {
 export type ResponseResolverReturnType<
   BodyType extends DefaultBodyType = undefined,
 > =
-  | (BodyType extends undefined ? Response : StrictResponse<BodyType>)
+  | ([BodyType] extends [undefined] ? Response : StrictResponse<BodyType>)
   | undefined
   | void
 
@@ -265,7 +265,7 @@ export abstract class RequestHandler<
 
           // Clone the previously stored response from the generator
           // so that it could be read again.
-          return this.resolverGeneratorResult.clone()
+          return this.resolverGeneratorResult.clone() as StrictResponse<any>
         }
 
         if (!this.resolverGenerator) {
diff --git a/test/typings/regressions/response-body-type.test-d.ts b/test/typings/regressions/response-body-type.test-d.ts
new file mode 100644
index 000000000..2c462dd17
--- /dev/null
+++ b/test/typings/regressions/response-body-type.test-d.ts
@@ -0,0 +1,10 @@
+/**
+ * @see https://github.com/mswjs/msw/issues/1823
+ */
+import { http, Path, HttpResponse, DefaultBodyType } from 'msw'
+
+function myHandler<CustomResponseBodyType extends DefaultBodyType>(path: Path) {
+  return (response: CustomResponseBodyType) => {
+    http.get(path, () => HttpResponse.json(response))
+  }
+}