[generator] Use + for nested types, not /

[jonpryor]

Context: dotnet/android#9747
Context: https://discord.com/channels/732297728826277939/732297837953679412/1336353039031734352
Context: https://discord.com/channels/732297728826277939/732297837953679412/1336358257769316372

The [Register] attribute provides "connector method" names, and for interface methods this will also include the name of the type which declares the method, which itself may be in a nested type:

namespace Android.App {
  public partial class Application {
    public partial interface IActivityLifecycleCallbacks : IJavaObject, IJavaPeerable {
      [Register (
          name: "onActivityCreated",
          signature: "(Landroid/app/Activity;Landroid/os/Bundle;)V",
          connector: "GetOnActivityCreated_Landroid_app_Activity_Landroid_os_Bundle_Handler:Android.App.Application/IActivityLifecycleCallbacksInvoker, Mono.Android, Version=0.0.0.0, Culture=neutral, PublicKeyToken=null")]
      void OnActivityCreated (Android.App.Activity activity, Android.OS.Bundle? savedInstanceState);

      // …
    }
  }
}

This output has been largely unchanged for years, but there is a problem with it: the connector parameter contains a nested type, and uses / to separate the "outer" type from the "inner" type.

This works on MonoVM.

This fails on NativeAOT and CoreCLR:

Could not resolve type 'Android.App.Application/IActivityLifecycleCallbacksInvoker' in assembly 'Mono.Android, Version=0.0.0.0, Culture=neutral, PublicKeyToken=84e04ff9cfb79065'.

The / needs to be a + in order for Type.GetType() to find it:

[Register (
    name: "onActivityCreated",
    signature: "(Landroid/app/Activity;Landroid/os/Bundle;)V",
    connector: "GetOnActivityCreated_Landroid_app_Activity_Landroid_os_Bundle_Handler:Android.App.Application+IActivityLifecycleCallbacksInvoker, Mono.Android, Version=0.0.0.0, Culture=neutral, PublicKeyToken=null")]
void OnActivityCreated (Android.App.Activity activity, Android.OS.Bundle? savedInstanceState);

Update generator so that + is used within the connector parameter.

However, to maintain compatibility with existing binding assemblies, update Java.Interop.Tools.JavaCallableWrappers so that it replaces / with + on import, so that the resulting Java Callable Wrappers contain + and not /:

// Java Callable Wrapper
/* partial */ class MauiApplication_ActivityLifecycleCallbacks
{
  public static final String __md_methods;
  static {
    __md_methods =
      // …
      "n_onActivityCreated:(Landroid/app/Activity;Landroid/os/Bundle;)V:GetOnActivityCreated_Landroid_app_Activity_Landroid_os_Bundle_Handler:Android.App.Application+IActivityLifecycleCallbacksInvoker, Mono.Android, Version=0.0.0.0, Culture=neutral, PublicKeyToken=null\n" +
      // …
      "";
    mono.android.Runtime.register ("Microsoft.Maui.MauiApplication+ActivityLifecycleCallbacks, Microsoft.Maui", MauiApplication_ActivityLifecycleCallbacks.class, __md_methods);
  }
}

[jonpryor]

/azp run

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Copilot reviewed 5 out of 9 changed files in this pull request and generated no comments.

Files not reviewed (4)

• tests/generator-Tests/Unit-Tests/CodeGeneratorExpectedResults/JavaInterop1/WriteNestedInterfaceTypes.txt: Language not supported
• tests/generator-Tests/Unit-Tests/CodeGeneratorExpectedResults/XAJavaInterop1/WriteNestedInterfaceTypes.txt: Language not supported
• tests/generator-Tests/Unit-Tests/DefaultInterfaceMethodsTests.cs: Evaluated as low risk
• tests/generator-Tests/expected.xaji/AccessModifiers/Xamarin.Test.PublicClass.cs: Evaluated as low risk

[jonathanpeppers]

I don't follow what's happening in the CI build, but seems like these changes wouldn't cause it?

[jonpryor]

Indeed, I don't see how the changes in the PR would cause the build breakage on .NET Windows, and yet it does! #1303 builds without error.

[jonpryor]

/azp run

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[jonpryor]

/azp run

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[jonpryor]

This approach became an annoying boondoggle once I tried to integrate with Android: dotnet/android#9750

• The changes to [Register] were (properly!) considered an API breaking change within Mono.Android.dll, which required updating acceptable-breakages-vReference-net10.0.txt to the tune of ~600 (!) entries
• The changes to [Register] "broke" various pieces of linker-related code, such as MarshalMethodsClassififier and the linker itself. The fact that [Register] contained "IL-syntax" type names made it much easier to lookup types with Cecil. Attempting to change to Reflection syntax required finding all the places that performed such a lookup, which took a while (assuming I even found them all)
• The changes to [Register] aren't required anyway! As initially mentioned, all existing binding assemblies are using IL syntax, so we have to fix them anyway!

#1304 just updates Java.Interop.Tools.JavaCallableWrappers so that generator output is unchanged. [Register] will continue to use IL nested type syntax, and That's Fine™. It results in a much smaller change to everything else.