Custom naming convention for generated code

[BalassaMarton]

As a developer, I'd like to customize the orchestrator/activity name that is generated for my classes annotated with DurableTaskAttribute.
The generator currently uses the target type's local name by default. This is not sufficient if there are many unrelated orchestrators and activities in the project in different namespaces, or if the Task Hub is shared between multiple services (for whatever reason).
The best would be a few properties that I can pass to the build from the project file, e.g.

<PropertyGroup>
    <!-- Configure the default for orchestrators, activities and events -->
    <DurableTaskDefaultNamingPolicy>FullName</DurableTaskDefaultNamingPolicy>

    <!-- Configure the default for orchestrators separately -->
    <DurableTaskOrchestratorDefaultNamingPolicy>FullName</DurableTaskOrchestratorDefaultNamingPolicy>
</PropertyGroup>

Possible values can be Name (current behavior), FullName, AssemblyQualifiedName - the names should be generated using the corresponding property of the target Type.

The current workaround is to always provide the name in the DurableTask annotation.

[BalassaMarton]

Looking deeper into how this works, this cannot be implemented solely in the generator, more like on the level of the attributes. How about adding a DurableTaskAttributeBase abstract type with a GetTaskName method? This would be backwards compatible because the existing DurableTaskAttribute would just return its Name, and alternative implementations could return the full name or anything they want. The generator will only work with the built-in DurableTaskAttribute, since it can't call the runtime method, but that should be fine because re-implementing this generator is not that hard anyway.

[BalassaMarton]

Further elaborating on this. Maybe even the generated code could just call the abstract GetTaskName method on the attribute. After all, the TaskName is for identifying the tasks, not for generating the method name (the generator is still a preview feature, so this breaking change would be expected). So for example:

// DurableTaskAttributeBase
public abstract class DurableTaskAttributeBase : Attribute
{
    public abstract TaskName GetTaskName(Type type);
}

// CustomDurableTaskAttribute.cs
public sealed class CustomDurableTaskAttribute : DurableTaskAttributeBase
{
    public override TaskName GetTaskName(Type type) => type.FullName;
}

// MyActivity.cs
namespace MyNamespace;

[CustomDurableTask]
internal sealed class MyActivity : TaskActivity<string, string>
{
    // ...
}

// DurableTaskExtensions.cs
public static partial class DurableTaskExtensions
{
    public static TaskName GetTaskName(this Type type)
    {
        var attribute = Attribute.GetCustomAttribute(type, typeof(DurableTaskAttributeBase));
        
        return attribute?.GetTaskName(type) switch
        {
            TaskName { Name: not null and not "" } taskName => taskName,
            _ => new TaskName(type.Name),
        };
    }
}

// GeneratedDurableTaskExtensions.cs
public static class GeneratedDurableTaskExtensions
{
        public static Task<string> CallMyActivityAsync(this TaskOrchestrationContext ctx, string input, TaskOptions? options = null)
    {
        return ctx.CallActivityAsync<string>(typeof(MyNamespace.MyActivity).GetTaskName(), input, options);
    }