Elvis operator translated incorrectly in some cases

[iskiselev]

Elvis operator translated incorrectly in some cases. Here is test case:

//@useroslyn
using System;

public static class Program
{
    public static void Main()
    {
        WriteNullableTestStruct(new TestStructHolder(new TestStruct(10)));
        WriteNullableTestStruct(new TestStructHolder(null));
    }

    public static void WriteNullableTestStruct(TestStructHolder holder)
    {
        Console.WriteLine(holder.TestStruct?.Field);
    }
}

public class TestStructHolder
{
    public readonly TestStruct? TestStruct;

    public TestStructHolder(TestStruct? testStruct)
    {
        TestStruct = testStruct;
    }
}

public struct TestStruct
{
    public int Field { get; set; }

    public TestStruct(int fieldValue)
    {
        Field = fieldValue;
    }
}

Resiult:

  Expected: "10"
  But was:  "0"

Translation:

  function Program_WriteNullableTestStruct (holder) {
    $T02().WriteLine((
        (holder.TestStruct !== null)
           ? JSIL.Nullable_ValueOrDefault(null, new ($T01())()).TestStruct$Field$value
           : null)
    );
  }; 

[kg]

What would the correct translation be, do you think?

[iskiselev]

ILSPy decompilation:

    public static void WriteNullableTestStruct(TestStructHolder holder)
    {
        TestStruct? testStruct;
        Console.WriteLine(holder.TestStruct.HasValue ? new int?(testStruct.GetValueOrDefault().Field) : null);
    }

So, it should be something like:

  function Program_WriteNullableTestStruct (holder) {
    $T02().WriteLine((
        (holder.TestStruct !== null)
           ? JSIL.Nullable_ValueOrDefault(holder.TestStruct.MemberwiseClone(), new ($T01())()).TestStruct$Field$value
           : null)
    );
  }; 

[iskiselev]

Hm, interesting - we create structure each time when we call JSIL.Nullable_ValueOrDefault. Probably we should just pass type inside and construct instance only if we need.