Helidon 4.x: Public Getters In BuilderBase Bug

Hey everyone! Let's talk about a small hiccup we've found in Helidon 4.x, specifically when it comes to generated getter methods in the BuilderBase class. It's a bit of a head-scratcher, but we'll break it down together, okay?

The Core Issue: Access Restrictions and Generated Code

So, the main problem is this: when the code generator in Helidon 4.x processes a blueprint method that has the @Option.Access("") annotation, it generates a package-private setter method, which is precisely what we want for internal use. But, here's the kicker, the getter method, the one that retrieves the value, ends up being public. This can be a problem if you're trying to keep certain aspects of your code, like enums used for configuration, hidden from public view.

Think of it like this: you have a secret recipe (the enum) that only the kitchen staff (internal code) needs to know about. You want to make sure no one outside the kitchen can peek at the recipe. The @Option.Access("") annotation is like putting a lock on the door. The setter method, like the door, is locked. However, the getter, which is meant to be the peephole, is wide open to everyone.

Let's imagine a scenario where you're using an enum like SpanProcessorType to manage different types of span processors. You might want this enum to be used internally for configuring the processors, and you don't want developers using your library to directly see or interact with it. The problem we're facing is that even if you try to restrict access to the enum by using @Option.Access(""), the public getter method will still expose it. This kinda defeats the purpose of access control, right?

This situation arises when you're working with blueprints and the code generator, which is responsible for creating the builder classes. The generated builder classes usually include getter and setter methods for all the configuration options defined in the blueprint. The issue is that even when you use @Option.Access("") to restrict the setter method's access, the getter method is still public. The implication is that the enum type is publicly visible, potentially exposing internal implementation details.

Deep Dive into the Problem: An Example Scenario

Let's dive into a more concrete example. Imagine you're working with SpanProcessorConfigBlueprint. In this blueprint, you might have a method like this:

@Option.Configured
@Option.Required
@Option.Access("")
SpanProcessorType type();

In this case, SpanProcessorType is an enum used internally. You use @Option.Access("") to limit the visibility of the setter for the type property. You expect the generated setter to be package-private, which is correct. But you also expect the getter to be package-private, preventing developers from directly accessing the enum. However, the getter method is unexpectedly public, revealing the enum to anyone using your library.

So, what's the impact? Well, the primary impact is that it breaks encapsulation. It exposes implementation details to developers. This may create a tight coupling between your internal logic and the public API. It may make it difficult to change your internal implementation without potentially breaking backward compatibility, even though you're trying to keep it internal.

In essence, this behavior may run counter to the principle of least privilege. If you only need the enum internally, you shouldn't expose it publicly, should you? It's a leaky abstraction. This can be a significant concern when you're designing libraries or frameworks, as you want to maintain control over the API and prevent developers from relying on internal implementation details.

Steps to Reproduce the Issue

Reproducing this issue is straightforward, guys! All you have to do is:

1. Set Up Your Blueprint: Define a blueprint class with a method that uses @Option.Access("") and a return type that is an enum or other internal-use class.
2. Generate the Builder: Use the Helidon code generator to create the builder classes from your blueprint.
3. Examine the Generated Code: Inspect the generated builder class (e.g., SpanProcessorConfig.BuilderBase). You'll find that the setter for the property with @Option.Access("") is package-private, as expected. However, the getter is public.

This is the crux of the issue. It's a discrepancy between the intended access restriction and the actual generated code. And this could be especially noticeable if you have a complex configuration with a lot of interdependencies. And this is something that should be addressed in future versions of the framework, and we can improve our understanding of how the code generator works.

It's a subtle yet significant behavior change that can affect how developers interact with your APIs. And this is something we must keep in mind while using Helidon 4.x. It also shows the importance of carefully considering access levels when designing your APIs. So, that's pretty much it! It's something to be aware of when you're using Helidon 4.x and trying to manage internal configuration details.

Understanding the Code Generation Process

To fully grasp the issue, let's get a bit deeper into how the code generator works. Helidon's code generator is responsible for taking your blueprint definitions and automatically creating the builder classes. This is a huge time-saver, as it eliminates the need to write a lot of boilerplate code. However, this automation also means that if the code generator has a bug or a limitation, it can have a cascading effect on your code.

The code generator, in general, reads your blueprint files (which are Java interfaces with annotations like @Option.Configured, @Option.Required, and @Option.Access). It then creates the corresponding builder classes, which include:

• Fields: Private fields to store the configuration values.
• Getters: Public (or package-private, based on @Option.Access) methods to retrieve the configuration values.
• Setters: Public (or package-private, based on @Option.Access) methods to set the configuration values.
• Builder Methods: Methods to configure nested objects or lists.

The code generator uses annotations like @Option.Access("") to determine the access level for the generated methods. The problem is that the logic for applying the access restriction to the getter methods may be flawed, only affecting setters in this specific scenario.

One possible reason for this could be that the code generator is not correctly interpreting or applying the @Option.Access annotation to the getter methods. It might assume that all getter methods should be public, or it might be missing a specific check or logic to apply the access restriction correctly to the getter methods.

Potential Solutions and Workarounds

While this is a problem, there are a few workarounds that you can employ until the issue is resolved. These might not be perfect solutions, but they can help mitigate the problem.

1. Internal Packages: The simplest workaround is to move the problematic enum or class into a separate package within your internal code. This keeps the class out of public view, even if the getter is public. Then, you can reference the enum class using a fully qualified name. It ensures that the enum cannot be directly accessed by developers and it is a pragmatic approach, though it does not directly address the root cause.
2. Documentation and Warnings: Carefully document your API. Let your developers know that they should not rely on certain internal types. You could even use Javadoc comments to explicitly warn against using the getter method. This approach relies on the good behavior of your developers and isn't a robust solution, but it can help minimize the impact of the problem.
3. Reflection (Use with Caution): You could use reflection to access the private fields or methods, but this is generally not recommended. Reflection breaks encapsulation and makes your code more fragile. Only use it as a last resort. This is also a pragmatic approach, though it is not an ideal solution due to the reasons described above.
4. Manual Builder Customization: If possible, you can manually customize the generated builder class. You can change the getter's access level to package-private. This requires manual intervention, which can be time-consuming and difficult to maintain as you regenerate the builder over time. Also, it can introduce more maintenance headaches. Also, it might not be possible for all the projects, but it is something that could work.

The Bottom Line

So, in a nutshell, there's a little glitch in Helidon 4.x. It generates public getter methods for fields with @Option.Access(""), even though the corresponding setter is package-private. This means that internal implementation details may be exposed. Keep these in mind, and hopefully, a fix will be available soon. In the meantime, use the workarounds to keep your code safe. Remember to always keep your code well-documented and to use the right access modifiers to maintain encapsulation.

Keep your eye out for updates on this issue. And remember to provide feedback to the Helidon team so they can fix it! We're all in this together, guys!

Happy coding!