Add BeanFactoryContribution for bean registrations

This commits adds an implementation that takes care of contributing
code for each bean definition in the bean factory, invoking
BeanRegistrationContributionProvider to determine the best candidate to
use.

Closes gh-28088

spring-beans/src/test/java/org/springframework/beans/factory/generator/BeanDefinitionsContributionTests.java

@@ -0,0 +1,122 @@
+/*
+ * Copyright 2002-2022 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.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.beans.factory.generator;
+
+import java.util.List;
+
+import org.junit.jupiter.api.Test;
+import org.mockito.ArgumentMatchers;
+import org.mockito.BDDMockito;
+import org.mockito.Mockito;
+
+import org.springframework.aot.generator.DefaultGeneratedTypeContext;
+import org.springframework.aot.generator.GeneratedType;
+import org.springframework.aot.generator.GeneratedTypeContext;
+import org.springframework.beans.factory.support.BeanDefinitionBuilder;
+import org.springframework.beans.factory.support.DefaultListableBeanFactory;
+import org.springframework.beans.factory.support.RootBeanDefinition;
+import org.springframework.javapoet.ClassName;
+import org.springframework.javapoet.support.CodeSnippet;
+
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatThrownBy;
+
+/**
+ * Tests for {@link BeanDefinitionsContribution}.
+ *
+ * @author Stephane Nicoll
+ */
+class BeanDefinitionsContributionTests {
+
+	@Test
+	void contributeThrowsContributionNotFoundIfNoContributionIsAvailable() {
+		DefaultListableBeanFactory beanFactory = new DefaultListableBeanFactory();
+		beanFactory.registerBeanDefinition("test", new RootBeanDefinition());
+		BeanDefinitionsContribution contribution = new BeanDefinitionsContribution(beanFactory,
+				List.of(Mockito.mock(BeanRegistrationContributionProvider.class)));
+		BeanFactoryInitialization initialization = new BeanFactoryInitialization(createGenerationContext());
+		assertThatThrownBy(() -> contribution.applyTo(initialization))
+				.isInstanceOfSatisfying(BeanRegistrationContributionNotFoundException.class, ex -> {
+					assertThat(ex.getBeanName()).isEqualTo("test");
+					assertThat(ex.getBeanDefinition()).isSameAs(beanFactory.getMergedBeanDefinition("test"));
+				});
+	}
+
+	@Test
+	void contributeThrowsBeanRegistrationExceptionIfContributionThrowsException() {
+		DefaultListableBeanFactory beanFactory = new DefaultListableBeanFactory();
+		beanFactory.registerBeanDefinition("test", new RootBeanDefinition());
+		BeanFactoryContribution testContribution = Mockito.mock(BeanFactoryContribution.class);
+		IllegalStateException testException = new IllegalStateException();
+		BDDMockito.willThrow(testException).given(testContribution).applyTo(ArgumentMatchers.any(BeanFactoryInitialization.class));
+		BeanDefinitionsContribution contribution = new BeanDefinitionsContribution(beanFactory,
+				List.of(new TestBeanRegistrationContributionProvider("test", testContribution)));
+		BeanFactoryInitialization initialization = new BeanFactoryInitialization(createGenerationContext());
+		assertThatThrownBy(() -> contribution.applyTo(initialization))
+				.isInstanceOfSatisfying(BeanDefinitionGenerationException.class, ex -> {
+					assertThat(ex.getBeanName()).isEqualTo("test");
+					assertThat(ex.getBeanDefinition()).isSameAs(beanFactory.getMergedBeanDefinition("test"));
+					assertThat(ex.getCause()).isEqualTo(testException);
+				});
+	}
+
+	@Test
+	void contributeGeneratesBeanDefinitionsInOrder() {
+		DefaultListableBeanFactory beanFactory = new DefaultListableBeanFactory();
+		beanFactory.registerBeanDefinition("counter", BeanDefinitionBuilder
+				.rootBeanDefinition(Integer.class, "valueOf").addConstructorArgValue(42).getBeanDefinition());
+		beanFactory.registerBeanDefinition("name", BeanDefinitionBuilder
+				.rootBeanDefinition(String.class).addConstructorArgValue("Hello").getBeanDefinition());
+		CodeSnippet code = contribute(beanFactory, createGenerationContext());
+		assertThat(code.getSnippet()).isEqualTo("""
+				BeanDefinitionRegistrar.of("counter", Integer.class).withFactoryMethod(Integer.class, "valueOf", int.class)
+						.instanceSupplier((instanceContext) -> instanceContext.create(beanFactory, (attributes) -> Integer.valueOf(attributes.get(0)))).customize((bd) -> bd.getConstructorArgumentValues().addIndexedArgumentValue(0, 42)).register(beanFactory);
+				BeanDefinitionRegistrar.of("name", String.class).withConstructor(String.class)
+						.instanceSupplier((instanceContext) -> instanceContext.create(beanFactory, (attributes) -> new String(attributes.get(0, String.class)))).customize((bd) -> bd.getConstructorArgumentValues().addIndexedArgumentValue(0, "Hello")).register(beanFactory);
+				""");
+	}
+
+	private CodeSnippet contribute(DefaultListableBeanFactory beanFactory, GeneratedTypeContext generationContext) {
+		BeanDefinitionsContribution contribution = new BeanDefinitionsContribution(beanFactory);
+		BeanFactoryInitialization initialization = new BeanFactoryInitialization(generationContext);
+		contribution.applyTo(initialization);
+		return CodeSnippet.of(initialization.toCodeBlock());
+	}
+
+	private GeneratedTypeContext createGenerationContext() {
+		return new DefaultGeneratedTypeContext("com.example", packageName ->
+				GeneratedType.of(ClassName.get(packageName, "Test")));
+	}
+
+	static class TestBeanRegistrationContributionProvider implements BeanRegistrationContributionProvider {
+
+		private final String beanName;
+
+		private final BeanFactoryContribution contribution;
+
+		public TestBeanRegistrationContributionProvider(String beanName, BeanFactoryContribution contribution) {
+			this.beanName = beanName;
+			this.contribution = contribution;
+		}
+
+		@Override
+		public BeanFactoryContribution getContributionFor(String beanName, RootBeanDefinition beanDefinition) {
+			return (beanName.equals(this.beanName) ? this.contribution : null);
+		}
+	}
+
+}