THRIFT-5823 Fix illegal uses of exceptions as normal struct type
Patch: Jens Geyer

This closes #1928
diff --git a/lib/go/test/ClientMiddlewareExceptionTest.thrift b/lib/go/test/ClientMiddlewareExceptionTest.thrift
index 647c433..b48a611 100644
--- a/lib/go/test/ClientMiddlewareExceptionTest.thrift
+++ b/lib/go/test/ClientMiddlewareExceptionTest.thrift
@@ -25,11 +25,11 @@
 
 // This is a special case, we want to make sure that the middleware don't
 // accidentally pull result as error.
-exception FooResponse {
+struct/*exception*/ FooResponse {      // returning an exception by any means other than "throws" is illegal
 }
 
 service ClientMiddlewareExceptionTest {
-  FooResponse foo() throws(
+  FooResponse foo() throws(            // returning an exception by any means other than "throws" is illegal
       1: Exception1 error1,
       2: Exception2 error2,
   )