Add tests for generic struct

Author: buyaa-n

src/libraries/System.Runtime/tests/System/Reflection/NullabilityInfoContextTests.cs

@@ -861,6 +861,15 @@ public static IEnumerable<object[]> NestedGenericsReturnParameterData()
             // public IEnumerable<Tuple<Tuple<string, object?>, int>?> MethodReturnsEnumerableNonTupleNonNonNullTupleNonNullNon() => null!;
             yield return new object[] { "MethodReturnsEnumerableNonTupleNonNonNullTupleNonNullNon",
                 NullabilityState.NotNull, NullabilityState.NotNull, NullabilityState.NotNull, NullabilityState.Nullable, NullabilityState.NotNull, NullabilityState.Nullable };
+            // public IEnumerable<GenericStruct<Tuple<string, object?>?, int>?>? MethodReturnsEnumerableNullStructNullNonNonTupleNonNullNull() => null;
+            yield return new object[] { "MethodReturnsEnumerableNullStructNullNonNullTupleNonNullNull",
+                NullabilityState.Nullable, NullabilityState.Nullable, NullabilityState.NotNull, NullabilityState.Nullable, NullabilityState.NotNull, NullabilityState.Nullable };
+            // public IEnumerable<Tuple<GenericStruct<string, object?>?, int>?>? MethodReturnsEnumerableNullTupleNullNonNullStructNonNullNull() => null;
+            yield return new object[] { "MethodReturnsEnumerableNullTupleNullNonNullStructNonNullNull",
+                NullabilityState.Nullable, NullabilityState.Nullable, NullabilityState.NotNull, NullabilityState.Nullable, NullabilityState.NotNull, NullabilityState.Nullable };
+            // public IEnumerable<(GenericStruct<string, object?> str, int? count)> MethodReturnsEnumerableNonValueTupleNonNullNonTupleNonNullNon() => null!;
+            yield return new object[] { "MethodReturnsEnumerableNonValueTupleNonNullNonStructNonNullNon",
+                NullabilityState.NotNull, NullabilityState.NotNull, NullabilityState.Nullable, NullabilityState.NotNull, NullabilityState.NotNull, NullabilityState.Nullable };
         }
 
         [Theory]
@@ -1072,12 +1081,17 @@ public void MethodParametersUnknown(string s, IDictionary<Type, string[]> dict)
         public IEnumerable<Tuple<(string name, object? value), int>?> MethodReturnsEnumerableNonTupleNonNonNullValueTupleNonNullNon() => null!;
         public IEnumerable<Tuple<(string? name, object value)?, int>?>? MethodReturnsEnumerableNullTupleNullNonNullValueTupleNullNonNull() => null!;
         public IEnumerable<Tuple<Tuple<string, object?>, int>?> MethodReturnsEnumerableNonTupleNonNonNullTupleNonNullNon() => null!;
+        public IEnumerable<GenericStruct<Tuple<string, object?>?, int>?>? MethodReturnsEnumerableNullStructNullNonNullTupleNonNullNull() => null;
+        public IEnumerable<Tuple<GenericStruct<string, object?>?, int>?>? MethodReturnsEnumerableNullTupleNullNonNullStructNonNullNull() => null;
+        public IEnumerable<(GenericStruct<string, object?> str, int? count)> MethodReturnsEnumerableNonValueTupleNonNullNonStructNonNullNon() => null!;
         public void MethodNullNonNullNonNon(string? s, IDictionary<Type, string?[]> dict) { }
         public void MethodNonNullNonNullNotNull(string s, [NotNull] IDictionary<Type, string[]?>? dict) { dict = new Dictionary<Type, string[]?>(); }
         public void MethodNullNonNullNullNon(string? s, IDictionary<Type, string?[]?> dict) { }
         public void MethodAllowNullNonNonNonNull([AllowNull] string s, IDictionary<Type, string[]>? dict) { }
     }
 
+    public struct GenericStruct<T, Y> { }
+
     internal class GenericTest<T>
     {
 #nullable disable