Failed to translate DisplayClass in some special local function

[yyjdelete]

Tested with 6.0.0.5559-preview2

Orig Code

using System;

namespace ConsoleApp4
{
    public class CZZZ
    {
        static int count;

        static void Main()
        {
            Console.WriteLine(M1());
            Console.WriteLine(M2());
        }
        public static int M1()
        {
            count = 0;
            int _x;
            return M1_x();

            int M1_x()
            {
                TryGetX(out _x);
                if (++count == 1)
                {
                    M1_x();
                }
                return _x;
            }
        }

        public static int M2()
        {
            int _x;
            M2_x();
            return _x;

            void M2_x()
            {
                _x = 0;
            }
        }

        private static bool TryGetX(out int x)
        {
            x = count;
            return true;
        }
    }
}

Actual

M1: InvalidOperationException: Sequence contains no elements, maybe related to #1781

System.InvalidOperationException: Sequence contains no elements
   at System.Linq.Enumerable.First[TSource](IEnumerable`1 source)
   at ICSharpCode.Decompiler.IL.Transforms.TransformDisplayClassUsage.IsClosure(ILTransformContext context, ILVariable variable, ITypeDefinition& closureType, ILInstruction& initializer)
   at ICSharpCode.Decompiler.IL.Transforms.TransformDisplayClassUsage.Run(ILFunction function, ILTransformContext context)
   at ICSharpCode.Decompiler.CSharp.CSharpDecompiler.DecompileBody(IMethod method, EntityDeclaration entityDecl, DecompileRun decompileRun, ITypeResolveContext decompilationContext)

M1: After modified variable.HasInitialValue to variable.AddressCount > 0(which also fix #1781) in TransformDisplayClassUsage.cs, it not throw exception.

ILSpy/ICSharpCode.Decompiler/IL/Transforms/TransformDisplayClassUsage.cs

Line 167 in d8a0882

if (context.Settings.LocalFunctions && closureType?.Kind == TypeKind.Struct && variable.HasInitialValue && IsPotentialClosure(context, closureType)) {

But the scope of _x will be changed, and it will return 0 instead of 1 in new code.

public static int M1()
{
	count = 0;
	return M1_x();
	int M1_x()
	{
		TryGetX(out int _x);
		if (++count == 1)
		{
			M1_x();
		}
		return _x;
	}
}

M2: Maybe an variant of M1, it will not throw InvalidOperationException, but will hit some assert and see the return is lost.

public static int M2()
{
	M2();
	int _x;
//<--see the `return` is lost.
	void M2()
	{
		_x = 0;
	}
}

[siegfriedpammer]

For the method M2 I have added a fix to prevent removing the return statement.

@dgrunwald Do you have any idea how we could extend the DeclareVariables step to support correctly declaring variables captured in local functions that do not have any use-sites except the calls to the local function?