fixup: add trailing return type tests

Author: a-nogikh

clang/test/SemaCXX/attr-malloc_span.cpp

@@ -72,3 +72,31 @@ void TestGoodBadSpan() {
   // expected-note@+1 {{in instantiation of function template specialization 'produce_span<BadSpan>' requested here}}
   produce_span<BadSpan>();
 }
+
+// Ensure that trailing return types are also supported.
+__attribute__((malloc_span)) auto trailling_return_type(int size)  -> GoodSpan { // no-warning
+  return GoodSpan{};
+}
+
+template<typename T>
+// expected-warning@+2 {{'malloc_span' attribute only applies to functions that return span-like structures}}
+// expected-note@+1 {{returned struct/class has 1 fields, expected 2}}
+__attribute__((malloc_span)) auto templated_trailling_return_type()  -> T { // no-warning
+  return T{};
+}
+
+void TestGoodBadTrailingReturnType() {
+  templated_trailling_return_type<GoodSpan>(); // no-warnings
+  // expected-note@+1 {{in instantiation of function template specialization 'templated_trailling_return_type<BadSpan>' requested here}}
+  templated_trailling_return_type<BadSpan>();
+}
+
+__attribute((malloc_span)) auto trailling_return_temmplate_good(void) -> Pair<int*, int> { // no-warning
+  return Pair<int*, int>{};
+}
+
+// expected-warning@+2 {{attribute only applies to functions that return span-like structures}}
+// expected-note@+1 {{returned struct/class fields are not a supported combination for a span-like type}}
+__attribute((malloc_span)) auto trailling_return_temmplate_bad(void) -> Pair<int, int> {
+  return Pair<int, int>{};
+}