CGLIB proxies are not used at runtime on `@Configuration` classes in AOT mode

[sdeleuze]

Consider the following configuration class:

@Configuration
public class MyConfiguration {
	@Bean
	A a() { return new A(); }

	@Bean
	B b() { return new B(this.a()); }
	
	static class A {
		public A() { System.out.println("A constructor"); }
	}

	static class B {
		public B(A a) { System.out.println("B constructor"); }
	}
}

On JVM in regular mode, it prints:

A constructor
B constructor

On JVM in AOT mode or native, while it seems CGLIB proxies are generated correctly at build time, but they seems not used since it prints:

A constructor
A constructor
B constructor

The code generated AOT maybe needs to be updated to leverage those CGLIB proxies.

[snicoll]

We need to swap the creation of the raw class to the cglib proxy. I was hoping I could avoid having to change code generation for this but it turns out that there isn't a way to achieve this using an instance supplier.

I've a proposal in 3b8bcdf.

This is blocked by spring-projects/spring-boot#32304 and, to some extent, #29141

[snicoll]

I have it working but I think it needs a bit more work to test it correctly.