Fix one symptom of the non-generic tuple type issue

Fixes dotnet#20494
Adds a test for dotnet#20583

src/Compilers/CSharp/Portable/Binder/Semantics/OverloadResolution/OverloadResolution.cs

@@ -1782,8 +1782,8 @@ private static BetterResult MoreSpecificType(TypeSymbol t1, TypeSymbol t2, ref H
  // argument is more specific and no type argument is less specific than the
  // corresponding type argument in the other. 
 
- var n1 = t1 as NamedTypeSymbol;
- var n2 = t2 as NamedTypeSymbol;
+ var n1 = t1.TupleUnderlyingTypeOrSelf() as NamedTypeSymbol;
+ var n2 = t2.TupleUnderlyingTypeOrSelf() as NamedTypeSymbol;
  Debug.Assert(((object)n1 == null) == ((object)n2 == null));
 
  if ((object)n1 == null)

src/Compilers/CSharp/Test/Emit/CodeGen/CodeGenTupleTest.cs

@@ -23415,7 +23415,7 @@ void M()
 
  [Fact]
  [WorkItem(20494, "https://github.com/dotnet/roslyn/issues/20494")]
- public void MoreGenericTieBreaker()
+ public void MoreGenericTieBreaker_01()
  {
  var source =
 @"using System;
@@ -23436,8 +23436,34 @@ public static void Main()
  public static void M2<T>(ValueTuple<ValueTuple<T, int>, int> a) { Console.Write(4); }
 }
 
-public class A<T> { }" + trivial2uple + tupleattributes_cs;
- var comp = CompileAndVerify(source, expectedOutput: "24");
+public class A<T> {}";
+ var comp = CompileAndVerify(source, additionalRefs: s_valueTupleRefs, expectedOutput: "24");
+ }
+
+ [Fact(Skip = "https://github.com/dotnet/roslyn/issues/20583")]
+ [WorkItem(20494, "https://github.com/dotnet/roslyn/issues/20494")]
+ [WorkItem(20583, "https://github.com/dotnet/roslyn/issues/20583")]
+ public void MoreGenericTieBreaker_02()
+ {
+ var source =
+@"using System;
+public class C
+{
+ public static void Main()
+ {
+ // var b = (1, 2, 3, 4, 5, 6, 7, 8);
+ var b = new ValueTuple<int, int, int, int, int, int, int, ValueTuple<int>>(1, 2, 3, 4, 5, 6, 7, new ValueTuple<int>(8));
+ M1(b);
+ M2(b); // ok, should select M2<T1, T2, T3, T4, T5, T6, T7, T8>(ValueTuple<T1, T2, T3, T4, T5, T6, T7, ValueTuple<T8>> a)
+ }
+ public static void M1<T1, T2, T3, T4, T5, T6, T7, TRest>(ValueTuple<T1, T2, T3, T4, T5, T6, T7, TRest> a) where TRest : struct { Console.Write(1); }
+ public static void M2<T1, T2, T3, T4, T5, T6, T7, T8>(ValueTuple<T1, T2, T3, T4, T5, T6, T7, ValueTuple<T8>> a) { Console.Write(2); }
+ public static void M2<T1, T2, T3, T4, T5, T6, T7, TRest>(ValueTuple<T1, T2, T3, T4, T5, T6, T7, TRest> a) where TRest : struct { Console.Write(3); }
+}
+";
+ var comp = CompileAndVerify(source,
+ additionalRefs: s_valueTupleRefs,
+ expectedOutput: @"12");
  }
  }
 }