Retain previous factory method in case of nested invocation with AOT

This commit harmonizes the invocation of a bean supplier with what
SimpleInstantiationStrategy does. Previously, the current factory method
was set to `null` once the invocation completes. This did not take
into account recursive scenarios where an instance supplier triggers
another instance supplier.

For consistency, the thread local is removed now if we attempt to set
the current method to null. SimpleInstantiationStrategy itself uses
the shortcut to align the code as much as possible.

Closes gh-33180

spring-beans/src/test/java/org/springframework/beans/factory/aot/BeanInstanceSupplierTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2023 the original author or authors.
+ * Copyright 2002-2024 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -25,6 +25,7 @@ import java.util.ArrayList;
 import java.util.List;
 import java.util.Map;
 import java.util.Set;
+import java.util.concurrent.atomic.AtomicReference;
 import java.util.function.Consumer;
 import java.util.stream.Stream;
 
@@ -51,6 +52,7 @@ import org.springframework.beans.factory.support.DefaultListableBeanFactory;
 import org.springframework.beans.factory.support.InstanceSupplier;
 import org.springframework.beans.factory.support.RegisteredBean;
 import org.springframework.beans.factory.support.RootBeanDefinition;
+import org.springframework.beans.factory.support.SimpleInstantiationStrategy;
 import org.springframework.core.env.Environment;
 import org.springframework.core.io.DefaultResourceLoader;
 import org.springframework.core.io.ResourceLoader;
@@ -292,6 +294,33 @@ class BeanInstanceSupplierTests {
 		assertThat(instance).isEqualTo("1");
 	}
 
+	@Test // gh-33180
+	void getWithNestedInvocationRetainsFactoryMethod() throws Exception {
+		AtomicReference<Method> testMethodReference = new AtomicReference<>();
+		AtomicReference<Method> anotherMethodReference = new AtomicReference<>();
+
+		BeanInstanceSupplier<Object> nestedInstanceSupplier = BeanInstanceSupplier
+				.forFactoryMethod(AnotherTestStringFactory.class, "another")
+				.withGenerator(registeredBean -> {
+					anotherMethodReference.set(SimpleInstantiationStrategy.getCurrentlyInvokedFactoryMethod());
+					return "Another";
+				});
+		RegisteredBean nestedRegisteredBean = new Source(String.class, nestedInstanceSupplier).registerBean(this.beanFactory);
+		BeanInstanceSupplier<Object> instanceSupplier = BeanInstanceSupplier
+				.forFactoryMethod(TestStringFactory.class, "test")
+				.withGenerator(registeredBean -> {
+					Object nested = nestedInstanceSupplier.get(nestedRegisteredBean);
+					testMethodReference.set(SimpleInstantiationStrategy.getCurrentlyInvokedFactoryMethod());
+					return "custom" + nested;
+				});
+		RegisteredBean registeredBean = new Source(String.class, instanceSupplier).registerBean(this.beanFactory);
+		Object value = instanceSupplier.get(registeredBean);
+
+		assertThat(value).isEqualTo("customAnother");
+		assertThat(testMethodReference.get()).isEqualTo(instanceSupplier.getFactoryMethod());
+		assertThat(anotherMethodReference.get()).isEqualTo(nestedInstanceSupplier.getFactoryMethod());
+	}
+
 	@Test
 	void resolveArgumentsWithNoArgConstructor() {
 		RootBeanDefinition beanDefinition = new RootBeanDefinition(
@@ -1030,4 +1059,18 @@ class BeanInstanceSupplierTests {
 
 	}
 
+	static class TestStringFactory {
+
+		String test() {
+			return "test";
+		}
+	}
+
+	static class AnotherTestStringFactory {
+
+		String another() {
+			return "another";
+		}
+	}
+
 }