C#: Add regression test

Author: hvitved

csharp/ql/test/library-tests/regressions/Program.cs

@@ -1,4 +1,4 @@
-
+// semmle-extractor-options: /langversion:8.0
 
 using System;
 using System.Threading.Tasks;
@@ -180,4 +180,13 @@ void F()
     }
 }
 
+class TupleMatching
+{
+    (int, object) G(object o1, object o2)
+    {
+        (object, object)? pair = (o1, o2);
+        return (0, pair is var (x, y) ? x : null);
+    }
+}
+
 // semmle-extractor-options: /r:System.Dynamic.Runtime.dll

csharp/ql/test/library-tests/regressions/TypeMentions.expected

@@ -82,3 +82,12 @@
 | Program.cs:169:5:169:10 | String |
 | Program.cs:174:5:174:8 | Void |
 | Program.cs:176:17:176:19 | IDisposable |
+| Program.cs:185:5:185:17 | (Int32,Object) |
+| Program.cs:185:6:185:8 | Int32 |
+| Program.cs:185:11:185:16 | Object |
+| Program.cs:185:21:185:26 | Object |
+| Program.cs:185:32:185:37 | Object |
+| Program.cs:187:9:187:24 | (Object,Object) |
+| Program.cs:187:9:187:25 | Nullable<(Object,Object)> |
+| Program.cs:187:10:187:15 | Object |
+| Program.cs:187:18:187:23 | Object |