Tuple reference compiles without System.Runtime.dll

[cston]

The following compiles successfully without System.Runtime.dll and the tuple is treated as a class type: csc -t:library -r:System.ValueTuple.dll c.cs

class C
{
    static void M()
    {
        var o = (1, 2);
    }
}

[AlekseyTs]

Here is a unit-test:

        [Fact]
        public void Test()
        {
            var text = "public struct A {}";
            var compilation1 = CreateCompilationWithMscorlib(text, options: TestOptions.ReleaseDll);

            var compilation2 = CreateCompilation(@"
class Program
{
static void Main(A x) {}
}", options: TestOptions.ReleaseDll, references: new[] { compilation1.EmitToImageReference() } );

            //compilation2.VerifyEmitDiagnostics();

            var a = compilation2.GetTypeByMetadataName("A");

            Assert.True(a.BaseType.IsErrorType());
            Assert.Equal("System.ValueType[missing]", a.BaseType.ToTestDisplayString());
            Assert.Null(a.GetUseSiteDiagnostic());
            Assert.Equal(TypeKind.Struct, a.TypeKind);
        }

a.TypeKind erroneously reports TypeKind.Class, but has no use-site error.

[gafter]

@cston I suspect this is already fixed in #14161?

[cston]

@gafter No, this issue was discovered from #14161.