Add support for ImportAware callback

This commit adds a way for a BeanFactoryPostProcessor to participate to
AOT optimizations by contributing code that replaces its runtime
behaviour.

ConfigurationClassPostProcessor does implement this new interface and
computes a mapping of the ImportAware configuration classes. The mapping
is generated for latter reuse by ImportAwareAotBeanPostProcessor.

Closes gh-2811

spring-context/src/main/java/org/springframework/context/annotation/ConfigurationClassPostProcessor.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2021 the original author or authors.
+ * 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.
@@ -18,6 +18,7 @@ package org.springframework.context.annotation;
 
 import java.util.ArrayList;
 import java.util.Arrays;
+import java.util.HashMap;
 import java.util.HashSet;
 import java.util.LinkedHashMap;
 import java.util.LinkedHashSet;
@@ -25,10 +26,14 @@ import java.util.List;
 import java.util.Map;
 import java.util.Set;
 
+import javax.lang.model.element.Modifier;
+
 import org.apache.commons.logging.Log;
 import org.apache.commons.logging.LogFactory;
 
 import org.springframework.aop.framework.autoproxy.AutoProxyUtils;
+import org.springframework.aot.hint.ResourceHints;
+import org.springframework.aot.hint.TypeReference;
 import org.springframework.beans.PropertyValues;
 import org.springframework.beans.factory.BeanClassLoaderAware;
 import org.springframework.beans.factory.BeanDefinitionStoreException;
@@ -40,6 +45,9 @@ import org.springframework.beans.factory.config.BeanFactoryPostProcessor;
 import org.springframework.beans.factory.config.ConfigurableListableBeanFactory;
 import org.springframework.beans.factory.config.InstantiationAwareBeanPostProcessor;
 import org.springframework.beans.factory.config.SingletonBeanRegistry;
+import org.springframework.beans.factory.generator.AotContributingBeanFactoryPostProcessor;
+import org.springframework.beans.factory.generator.BeanFactoryContribution;
+import org.springframework.beans.factory.generator.BeanFactoryInitialization;
 import org.springframework.beans.factory.parsing.FailFastProblemReporter;
 import org.springframework.beans.factory.parsing.PassThroughSourceExtractor;
 import org.springframework.beans.factory.parsing.ProblemReporter;
@@ -65,6 +73,10 @@ import org.springframework.core.type.AnnotationMetadata;
 import org.springframework.core.type.MethodMetadata;
 import org.springframework.core.type.classreading.CachingMetadataReaderFactory;
 import org.springframework.core.type.classreading.MetadataReaderFactory;
+import org.springframework.javapoet.CodeBlock;
+import org.springframework.javapoet.CodeBlock.Builder;
+import org.springframework.javapoet.MethodSpec;
+import org.springframework.javapoet.ParameterizedTypeName;
 import org.springframework.lang.Nullable;
 import org.springframework.util.Assert;
 import org.springframework.util.ClassUtils;
@@ -89,7 +101,8 @@ import org.springframework.util.ClassUtils;
  * @since 3.0
  */
 public class ConfigurationClassPostProcessor implements BeanDefinitionRegistryPostProcessor,
-		PriorityOrdered, ResourceLoaderAware, ApplicationStartupAware, BeanClassLoaderAware, EnvironmentAware {
+		AotContributingBeanFactoryPostProcessor, PriorityOrdered, ResourceLoaderAware, ApplicationStartupAware,
+		BeanClassLoaderAware, EnvironmentAware {
 
 	/**
 	 * A {@code BeanNameGenerator} using fully qualified class names as default bean names.
@@ -269,6 +282,12 @@ public class ConfigurationClassPostProcessor implements BeanDefinitionRegistryPo
 		beanFactory.addBeanPostProcessor(new ImportAwareBeanPostProcessor(beanFactory));
 	}
 
+	@Override
+	public BeanFactoryContribution contribute(ConfigurableListableBeanFactory beanFactory) {
+		return (beanFactory.containsBean(IMPORT_REGISTRY_BEAN_NAME)
+				? new ImportAwareBeanFactoryConfiguration(beanFactory) : null);
+	}
+
 	/**
 	 * Build and validate a configuration model based on the registry of
 	 * {@link Configuration} classes.
@@ -485,4 +504,55 @@ public class ConfigurationClassPostProcessor implements BeanDefinitionRegistryPo
 		}
 	}
 
+	private static final class ImportAwareBeanFactoryConfiguration implements BeanFactoryContribution {
+
+		private final ConfigurableListableBeanFactory beanFactory;
+
+		private ImportAwareBeanFactoryConfiguration(ConfigurableListableBeanFactory beanFactory) {
+			this.beanFactory = beanFactory;
+		}
+
+
+		@Override
+		public void applyTo(BeanFactoryInitialization initialization) {
+			Map<String, String> mappings = buildImportAwareMappings();
+			if (!mappings.isEmpty()) {
+				MethodSpec method = initialization.generatedTypeContext().getMainGeneratedType()
+						.addMethod(beanPostProcessorMethod(mappings));
+				initialization.contribute(code -> code.addStatement("beanFactory.addBeanPostProcessor($N())", method));
+				ResourceHints resourceHints = initialization.generatedTypeContext().runtimeHints().resources();
+				mappings.forEach((target, importedFrom) -> resourceHints.registerType(
+						TypeReference.of(importedFrom)));
+			}
+		}
+
+		private MethodSpec.Builder beanPostProcessorMethod(Map<String, String> mappings) {
+			Builder code = CodeBlock.builder();
+			code.addStatement("$T mappings = new $T<>()", ParameterizedTypeName.get(
+					Map.class, String.class, String.class), HashMap.class);
+			mappings.forEach((key, value) -> code.addStatement("mappings.put($S, $S)", key, value));
+			code.addStatement("return new $T($L)", ImportAwareAotBeanPostProcessor.class, "mappings");
+			return MethodSpec.methodBuilder("createImportAwareBeanPostProcessor")
+					.returns(ImportAwareAotBeanPostProcessor.class)
+					.addModifiers(Modifier.PRIVATE).addCode(code.build());
+		}
+
+		private Map<String, String> buildImportAwareMappings() {
+			ImportRegistry ir = this.beanFactory.getBean(IMPORT_REGISTRY_BEAN_NAME, ImportRegistry.class);
+			Map<String, String> mappings = new LinkedHashMap<>();
+			for (String name : this.beanFactory.getBeanDefinitionNames()) {
+				Class<?> beanType = this.beanFactory.getType(name);
+				if (beanType != null && ImportAware.class.isAssignableFrom(beanType)) {
+					String type = ClassUtils.getUserClass(beanType).getName();
+					AnnotationMetadata importingClassMetadata = ir.getImportingClassFor(type);
+					if (importingClassMetadata != null) {
+						mappings.put(type, importingClassMetadata.getClassName());
+					}
+				}
+			}
+			return mappings;
+		}
+
+	}
+
 }

spring-context/src/main/java/org/springframework/context/annotation/ImportAwareAotBeanPostProcessor.java

@@ -0,0 +1,75 @@
+/*
+ * 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.context.annotation;
+
+import java.io.IOException;
+import java.util.Map;
+
+import org.springframework.beans.factory.config.BeanPostProcessor;
+import org.springframework.core.type.classreading.CachingMetadataReaderFactory;
+import org.springframework.core.type.classreading.MetadataReader;
+import org.springframework.core.type.classreading.MetadataReaderFactory;
+import org.springframework.lang.Nullable;
+import org.springframework.util.ClassUtils;
+
+/**
+ * A {@link BeanPostProcessor} that honours {@link ImportAware} callback using
+ * a mapping computed at build time.
+ *
+ * @author Stephane Nicoll
+ * @since 6.0
+ */
+public final class ImportAwareAotBeanPostProcessor implements BeanPostProcessor {
+
+	private final MetadataReaderFactory metadataReaderFactory;
+
+	private final Map<String, String> importsMapping;
+
+	public ImportAwareAotBeanPostProcessor(Map<String, String> importsMapping) {
+		this.metadataReaderFactory = new CachingMetadataReaderFactory();
+		this.importsMapping = Map.copyOf(importsMapping);
+	}
+
+	@Override
+	public Object postProcessBeforeInitialization(Object bean, String beanName) {
+		if (bean instanceof ImportAware) {
+			setAnnotationMetadata((ImportAware) bean);
+		}
+		return bean;
+	}
+
+	private void setAnnotationMetadata(ImportAware instance) {
+		String importingClass = getImportingClassFor(instance);
+		if (importingClass == null) {
+			return; // import aware configuration class not imported
+		}
+		try {
+			MetadataReader metadataReader = this.metadataReaderFactory.getMetadataReader(importingClass);
+			instance.setImportMetadata(metadataReader.getAnnotationMetadata());
+		}
+		catch (IOException ex) {
+			throw new IllegalStateException(String.format("Failed to read metadata for '%s'", importingClass), ex);
+		}
+	}
+
+	@Nullable
+	private String getImportingClassFor(ImportAware instance) {
+		String target = ClassUtils.getUserClass(instance).getName();
+		return this.importsMapping.get(target);
+	}
+
+}