Compilation fails when defining mapper as inner/nested class and the outer class has an attribute

Describe the bug When defining the mapper as an inner class, the generated mapper code is copying the existing class attributes and the parent class but not copying their respective namespace defined at the bottom. This is creating 2 problems:

1. The compilation fails because the attribute or the parent are not found (since it missing the using namespace). There is an open issue for this already (https://github.com/riok/mapperly/issues/507)
2. By copying the attribute/tag to the generated class, it generates a compilation error CS0579 Duplicate 'xyz' attribute since now both the original and the generated class are applying the same attribute/tag.

To Reproduce Steps to reproduce the behavior:

1. Create a class with an attribute
2. Declare a mapper as an inner class
3. Try to compile the code.

Expected behavior Code compiles without error

Code snippets

using Riok.Mapperly.Abstractions;
using System.Diagnostics.CodeAnalysis;
namespace Bug_Mapperly;

internal class Program { static void Main(string[] args) { Console.WriteLine("Hello, World!"); } }

[ExcludeFromCodeCoverage] // --The generated code will also have this attribute set and will show the 2 compilations errors mentioned above (Undefined ExcludeFromCodeCoverage because of lack of namespace import. If you use the fqn for ExcludeFromCodeCoverage as in the line below, you will get the duplicate attribute error
//[System.Diagnostics.CodeAnalysis.ExcludeFromCodeCoverage]
public partial class CarDto
{
    public string? Maker { get; set; }
    public string? Model { get; set; }
    [Mapper]
    private partial class CarMapper
    {
        public partial CarDto From(Car car);
    }
}
public class Car
{
    public string? Maker { get; set; }
    public string? Model { get; set; }
}

Fix suggestion

• Mapper should copy the using namespace code
• Mapper should not copy outer class attributes when generating the code

Environment (please complete the following information):

• Mapperly Version: 2.9.0-next.2
• .NET Version: .NET 6
• Target Framework: [e.g. .net6.0]
• IDE: Visual Studio Pro 2022
• OS: Windows 10

Additional context Related issues:

• Added support to inner classes: https://github.com/riok/mapperly/issues/350
• Lack of namespace import: https://github.com/riok/mapperly/issues/507

[renatosc]

Created new issue for the parent class issue: https://github.com/riok/mapperly/issues/548

[TimothyMakkison]

@TimothyMakkison , I didn’t mention on the issue but I see same similar behavior with inheritance, where the parent class is being copied when it I think it should not needed to be copied. Do you want me to create a new issue about that?

If its not too much effort then please do. Do you have a simple example you could share?