Missing `readonly` on ref-local can result in ArrayTypeMismatchException

[dgrunwald]

Input code

using System.Collections.Generic;

public class C {
    public static void Foo(in object a, object v) {}
    public static void M1(object[] arr) {
        Foo(in arr[1], new List<int>{1,2});
    }
    public static void Main() {
        string[] arr = new string[5];
        M1(arr);
    }
}

Erroneous output

If collection initializers are disabled, or if the second argument is another complex expression that the decompiler transforms into multiple statements:

    public static void M1(object[] arr)
    {
        ref object a = ref arr[1];
        List<int> list = new List<int>();
        list.Add(1);
        list.Add(2);
        Foo(ref a, list);
    }

In the original code, in arr[1] translates to readonly.ldelema. In the decompiled code, we get a non-readonly ldelema. This results in the decompiled program failing with ArrayTypeMismatchException when the original program was successful.

A correct decompilation would use:

    public static void M1(object[] arr)
    {
        ref readonly object a = ref arr[1];
        List<int> list = new List<int>();
        list.Add(1);
        list.Add(2);
        Foo(in a, list);
    }