Mapping string[] to string[] throws CS8081

Describe the bug Mapping string array to a string array throws a CS8081: “Expression does not have a name”.

The picture describes the error:

To Reproduce Steps to reproduce the behavior:

1. Use the code snippets and check the generated code

Expected behavior No CS8081 exception in the generated code. Also the generated code is different with no generated code header comment which is strange behavior?

Code snippets A.cs:

namespace Namespace;

using System;

public class A
{
	public string[] Items { get; set; }

	public A()
	{
		Items = Array.Empty<string>();
	}

	public A(string[] array)
	{
		Items = array;
	}
}

B.cs:

// //------------------------------------------------------------------------------
// // <auto-generated>
// //     This code was generated by a tool.
// //
// //     Changes to this file may cause incorrect behavior and will be lost if
// //     the code is regenerated.
// // </auto-generated>
// //------------------------------------------------------------------------------
namespace AnotherNamespace
{
	using System;

	public class A
	{
		public string[] Items { get; set; }

		public A()
		{
			Items = Array.Empty<string>();
		}

		public A(string[] array)
		{
			Items = array;
		}
	}
}

Mapper.cs:

namespace Namespace;

using Riok.Mapperly.Abstractions;

[Mapper]
public partial class Mapper
{
	public partial A AtoA(AnotherNamespace.A abcde);
}

Environment:

• Mapperly Version: 2.8.0
• .NET Version: .NET SDK 7.0.203
• Target Framework: net6.0
• IDE: Visual Studio v17.5.5
• OS: Windows 11 22H2

[TimothyMakkison]

Minimal example

[Mapper]
public static partial class Mapper
{
    public static partial int[] Map(int?[] value);
}

Simplified issue

[Mapper]
public static partial class Mapper
{
    public static partial A BtoA(B value);
}
public class A
{
    public string[] Items { get; set; } = Array.Empty<string>();
}
public class B
{
    public string?[] Items { get; set; } = Array.Empty<string>();
}

It also looks like a lot of tests are broken, Dictionary and Enumerable tests both generate invalid code.

[Sjoerdsjoerd]

I think beside the nullable problem, the main problem here is the nameof(source[i]) part, as an indexer is not valid inside a nameof expression.

@Sjoerdsjoerd I cannot reproduce the issue with the code you provided with v2.8.0/main and neither with enabled/disabled nullable reference types. Do you have UseDeepCloning, ThrowOnMappingNullMismatch, or ThrowOnPropertyMappingNullMismatch enabled? Do both properties have an accessible getter/setter? What nullable reference types settings do the classes Namespace.A and AnotherNamespace.A have?

@latonz No, the mapper I used was the default one. Same as in the snippet. I think the problem is when having both enabled and disabled nullable references. As @TimothyMakkison also acknowledge. Both properties have setters (see snippet). Nullable in csprojects is enabled for all classes. But I think that the header for generated code makes disables nullable.

After a bit of research, I came upon this doc that explains why it disables nullable for generate code: https://github.com/dotnet/roslyn/blob/main/docs/features/nullable-reference-types.md#generated-code