Merge branch '4.1.x'

Closes gh-51926

build-plugin/spring-boot-gradle-plugin/src/main/java/org/springframework/boot/gradle/plugin/JavaPluginAction.java

@@ -90,7 +90,7 @@ final class JavaPluginAction implements PluginApplicationAction {
 		configureBootTestRunTask(project, resolveMainTestClassName);
 		project.afterEvaluate(this::configureUtf8Encoding);
 		configureParametersCompilerArg(project);
-		configureAdditionalMetadataLocations(project);
+		configureConfigurationProcessorCompilerArgs(project);
 		configureSpringBootStarterTestToDependOnJUnitPlatformLauncher(project);
 	}
 
@@ -263,13 +263,13 @@ final class JavaPluginAction implements PluginApplicationAction {
 		});
 	}
 
-	private void configureAdditionalMetadataLocations(Project project) {
+	private void configureConfigurationProcessorCompilerArgs(Project project) {
 		project.afterEvaluate((evaluated) -> evaluated.getTasks()
 			.withType(JavaCompile.class)
-			.configureEach(this::configureAdditionalMetadataLocations));
+			.configureEach(this::configureConfigurationProcessorCompilerArgs));
 	}
 
-	private void configureAdditionalMetadataLocations(JavaCompile compile) {
+	private void configureConfigurationProcessorCompilerArgs(JavaCompile compile) {
 		SourceSetContainer sourceSets = compile.getProject()
 			.getExtensions()
 			.getByType(JavaPluginExtension.class)
@@ -278,7 +278,12 @@ final class JavaPluginAction implements PluginApplicationAction {
 			.filter((candidate) -> candidate.getCompileJavaTaskName().equals(compile.getName()))
 			.map((match) -> match.getResources().getSrcDirs())
 			.findFirst()
-			.ifPresent((locations) -> compile.doFirst(new AdditionalMetadataLocationsConfigurer(locations)));
+			.ifPresent((locations) -> {
+				File descriptionCache = new File(compile.getTemporaryDir(),
+						"previous-spring-configuration-metadata.json");
+				compile.getOutputs().file(descriptionCache);
+				compile.doFirst(new ConfigurationProcessorCompilerArgsConfigurer(locations, descriptionCache));
+			});
 	}
 
 	private void configureProductionRuntimeClasspathConfiguration(Project project) {
@@ -342,16 +347,19 @@ final class JavaPluginAction implements PluginApplicationAction {
 	}
 
 	/**
-	 * Task {@link Action} to add additional meta-data locations. We need to use an
-	 * inner-class rather than a lambda due to
-	 * https://github.com/gradle/gradle/issues/5510.
+	 * Task {@link Action} to add compiler args used by
+	 * {@code spring-boot-configuration-processor}. We need to use an inner-class rather
+	 * than a lambda due to https://github.com/gradle/gradle/issues/5510.
 	 */
-	private static final class AdditionalMetadataLocationsConfigurer implements Action<Task> {
+	private static final class ConfigurationProcessorCompilerArgsConfigurer implements Action<Task> {
 
 		private final Set<File> locations;
 
-		private AdditionalMetadataLocationsConfigurer(Set<File> locations) {
+		private final File descriptionCache;
+
+		private ConfigurationProcessorCompilerArgsConfigurer(Set<File> locations, File descriptionCache) {
 			this.locations = locations;
+			this.descriptionCache = descriptionCache;
 		}
 
 		@Override
@@ -361,6 +369,7 @@ final class JavaPluginAction implements PluginApplicationAction {
 			}
 			if (hasConfigurationProcessorOnClasspath(compile)) {
 				configureAdditionalMetadataLocations(compile);
+				configureDescriptionCacheLocation(compile);
 			}
 		}
 
@@ -379,6 +388,13 @@ final class JavaPluginAction implements PluginApplicationAction {
 						+ StringUtils.collectionToCommaDelimitedString(this.locations));
 		}
 
+		private void configureDescriptionCacheLocation(JavaCompile compile) {
+			compile.getOptions()
+				.getCompilerArgs()
+				.add("-Aorg.springframework.boot.configurationprocessor.descriptionCacheLocation="
+						+ this.descriptionCache.getAbsolutePath());
+		}
+
 	}
 
 }

build-plugin/spring-boot-gradle-plugin/src/test/java/org/springframework/boot/gradle/plugin/JavaPluginActionIntegrationTests.java

@@ -129,7 +129,7 @@ class JavaPluginActionIntegrationTests {
 	}
 
 	@TestTemplate
-	void additionalMetadataLocationsConfiguredWhenProcessorIsPresent() throws IOException {
+	void configurationPropertiesCompilerArgumentsConfiguredWhenProcessorIsPresent() throws IOException {
 		createMinimalMainSource();
 		File libs = new File(this.gradleBuild.getProjectDir(), "libs");
 		libs.mkdirs();
@@ -139,13 +139,19 @@ class JavaPluginActionIntegrationTests {
 		BuildTask task = result.task(":compileJava");
 		assertThat(task).isNotNull();
 		assertThat(task.getOutcome()).isEqualTo(TaskOutcome.SUCCESS);
-		assertThat(result.getOutput()).contains("compileJava compiler args: [-parameters, -Aorg.springframework.boot."
-				+ "configurationprocessor.additionalMetadataLocations="
-				+ new File(this.gradleBuild.getProjectDir(), "src/main/resources").getCanonicalPath());
+		assertThat(result.getOutput())
+			.contains("compileJava compiler args: [-parameters, -Aorg.springframework.boot."
+					+ "configurationprocessor.additionalMetadataLocations="
+					+ new File(this.gradleBuild.getProjectDir(), "src/main/resources").getCanonicalPath()
+					+ ", -Aorg.springframework.boot.configurationprocessor.descriptionCacheLocation="
+					+ new File(this.gradleBuild.getProjectDir(),
+							"build/tmp/compileJava/previous-spring-configuration-metadata.json")
+						.getCanonicalPath()
+					+ "]");
 	}
 
 	@TestTemplate
-	void additionalMetadataLocationsNotConfiguredWhenProcessorIsAbsent() throws IOException {
+	void configurationPropertiesCompilerArgumentsNotConfiguredWhenProcessorIsAbsent() throws IOException {
 		createMinimalMainSource();
 		BuildResult result = this.gradleBuild.build("compileJava");
 		BuildTask task = result.task(":compileJava");
@@ -154,6 +160,32 @@ class JavaPluginActionIntegrationTests {
 		assertThat(result.getOutput()).contains("compileJava compiler args: [-parameters]");
 	}
 
+	@TestTemplate
+	void descriptionCacheLocationIsAnOutputOfCompileJava() throws IOException {
+		createMinimalMainSource();
+		BuildResult result = this.gradleBuild.build("compileJava");
+		BuildTask task = result.task(":compileJava");
+		assertThat(task).isNotNull();
+		assertThat(task.getOutcome()).isEqualTo(TaskOutcome.SUCCESS);
+		assertThat(result.getOutput()).contains("compileJava outputs: ")
+			.contains(new File(this.gradleBuild.getProjectDir(),
+					"build/tmp/compileJava/previous-spring-configuration-metadata.json")
+				.getCanonicalPath());
+	}
+
+	@TestTemplate
+	void compileJavaIsUpToDateOnSecondInvocation() throws IOException {
+		createMinimalMainSource();
+		BuildResult result = this.gradleBuild.build("compileJava");
+		BuildTask task = result.task(":compileJava");
+		assertThat(task).isNotNull();
+		assertThat(task.getOutcome()).isEqualTo(TaskOutcome.SUCCESS);
+		result = this.gradleBuild.build("compileJava");
+		task = result.task(":compileJava");
+		assertThat(task).isNotNull();
+		assertThat(task.getOutcome()).isEqualTo(TaskOutcome.UP_TO_DATE);
+	}
+
 	@TestTemplate
 	void applyingJavaPluginCreatesDevelopmentOnlyConfiguration() {
 		assertThat(this.gradleBuild.build("help").getOutput()).contains("developmentOnly exists = true");

build-plugin/spring-boot-gradle-plugin/src/test/resources/org/springframework/boot/gradle/plugin/JavaPluginActionIntegrationTests-compileJavaIsUpToDateOnSecondInvocation.gradle

@@ -0,0 +1,20 @@
+/*
+ * Copyright 2012-present 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.
+ */
+
+plugins {
+	id 'java'
+	id 'org.springframework.boot' version '{version}'
+}

build-plugin/spring-boot-gradle-plugin/src/test/resources/org/springframework/boot/gradle/plugin/JavaPluginActionIntegrationTests-descriptionCacheLocationIsAnOutputOfCompileJava.gradle

@@ -0,0 +1,26 @@
+/*
+ * Copyright 2012-present 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.
+ */
+
+plugins {
+	id 'java'
+	id 'org.springframework.boot' version '{version}'
+}
+
+compileJava {
+	doLast {
+		println "${name} outputs: ${outputs.files.files}"
+	}
+}

configuration-metadata/spring-boot-configuration-processor/src/main/java/org/springframework/boot/configurationprocessor/ConfigurationMetadataAnnotationProcessor.java

@@ -21,6 +21,7 @@ import java.io.StringWriter;
 import java.time.Duration;
 import java.util.ArrayDeque;
 import java.util.Deque;
+import java.util.HashSet;
 import java.util.LinkedHashMap;
 import java.util.List;
 import java.util.Locale;
@@ -77,6 +78,8 @@ public class ConfigurationMetadataAnnotationProcessor extends AbstractProcessor
 
 	static final String ADDITIONAL_METADATA_LOCATIONS_OPTION = "org.springframework.boot.configurationprocessor.additionalMetadataLocations";
 
+	static final String DESCRIPTION_CACHE_LOCATION_OPTION = "org.springframework.boot.configurationprocessor.descriptionCacheLocation";
+
 	static final String CONFIGURATION_PROPERTIES_ANNOTATION = "org.springframework.boot.context.properties.ConfigurationProperties";
 
 	static final String CONFIGURATION_PROPERTIES_SOURCE_ANNOTATION = "org.springframework.boot.context.properties.ConfigurationPropertiesSource";
@@ -113,7 +116,8 @@ public class ConfigurationMetadataAnnotationProcessor extends AbstractProcessor
 
 	static final String ENDPOINT_ACCESS_ENUM = "org.springframework.boot.actuate.endpoint.Access";
 
-	private static final Set<String> SUPPORTED_OPTIONS = Set.of(ADDITIONAL_METADATA_LOCATIONS_OPTION);
+	private static final Set<String> SUPPORTED_OPTIONS = Set.of(ADDITIONAL_METADATA_LOCATIONS_OPTION,
+			DESCRIPTION_CACHE_LOCATION_OPTION);
 
 	private MetadataStore metadataStore;
 
@@ -123,6 +127,10 @@ public class ConfigurationMetadataAnnotationProcessor extends AbstractProcessor
 
 	private MetadataGenerationEnvironment metadataEnv;
 
+	private DescriptionCache descriptionCache;
+
+	private final Set<String> classFileBackedTypes = new HashSet<>();
+
 	protected String configurationPropertiesAnnotation() {
 		return CONFIGURATION_PROPERTIES_ANNOTATION;
 	}
@@ -189,6 +197,10 @@ public class ConfigurationMetadataAnnotationProcessor extends AbstractProcessor
 				configurationPropertiesSourceAnnotation(), nestedConfigurationPropertyAnnotation(),
 				deprecatedConfigurationPropertyAnnotation(), constructorBindingAnnotation(), autowiredAnnotation(),
 				defaultValueAnnotation(), endpointAnnotations(), readOperationAnnotation(), nameAnnotation());
+		String cacheLocation = env.getOptions().get(DESCRIPTION_CACHE_LOCATION_OPTION);
+		if (cacheLocation != null) {
+			this.descriptionCache = new DescriptionCache(cacheLocation);
+		}
 	}
 
 	@Override
@@ -289,6 +301,9 @@ public class ConfigurationMetadataAnnotationProcessor extends AbstractProcessor
 			Deque<TypeElement> seen) {
 		if (!seen.contains(element)) {
 			seen.push(element);
+			if (this.descriptionCache != null && !this.metadataEnv.hasSourceTree(element)) {
+				this.classFileBackedTypes.add(this.metadataEnv.getTypeUtils().getQualifiedName(element));
+			}
 			new PropertyDescriptorResolver(this.metadataEnv).resolve(element, source).forEach((descriptor) -> {
 				this.metadataCollector.add(descriptor.resolveItemMetadata(prefix, this.metadataEnv));
 				ItemHint itemHint = descriptor.resolveItemHint(prefix, this.metadataEnv);
@@ -405,14 +420,38 @@ public class ConfigurationMetadataAnnotationProcessor extends AbstractProcessor
 	protected ConfigurationMetadata writeMetadata() throws Exception {
 		ConfigurationMetadata metadata = this.metadataCollector.getMetadata();
 		metadata = mergeAdditionalMetadata(metadata, () -> this.metadataStore.readAdditionalMetadata());
+		fillCachedDescriptions(metadata);
 		removeIgnored(metadata);
 		if (!metadata.getItems().isEmpty()) {
 			this.metadataStore.writeMetadata(metadata);
+			updateDescriptionCache(metadata);
 			return metadata;
 		}
 		return null;
 	}
 
+	private void fillCachedDescriptions(ConfigurationMetadata metadata) {
+		if (this.descriptionCache == null) {
+			return;
+		}
+		for (ItemMetadata item : metadata.getItems()) {
+			if (item.isOfItemType(ItemMetadata.ItemType.PROPERTY) && item.getDescription() == null
+					&& item.getSourceType() != null && this.classFileBackedTypes.contains(item.getSourceType())) {
+				String cached = this.descriptionCache.getDescription(item.getName());
+				if (cached != null) {
+					item.setDescription(cached);
+				}
+			}
+		}
+	}
+
+	private void updateDescriptionCache(ConfigurationMetadata metadata) {
+		if (this.descriptionCache == null) {
+			return;
+		}
+		this.descriptionCache.update(metadata);
+	}
+
 	private void removeIgnored(ConfigurationMetadata metadata) {
 		for (ItemIgnore itemIgnore : metadata.getIgnored()) {
 			metadata.removeMetadata(itemIgnore.getType(), itemIgnore.getName());

configuration-metadata/spring-boot-configuration-processor/src/main/java/org/springframework/boot/configurationprocessor/DescriptionCache.java

@@ -0,0 +1,99 @@
+/*
+ * Copyright 2012-present 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.boot.configurationprocessor;
+
+import java.io.File;
+import java.io.FileInputStream;
+import java.io.FileOutputStream;
+import java.io.IOException;
+
+import org.springframework.boot.configurationprocessor.metadata.ConfigurationMetadata;
+import org.springframework.boot.configurationprocessor.metadata.ItemMetadata;
+import org.springframework.boot.configurationprocessor.metadata.JsonMarshaller;
+
+/**
+ * Cache for property descriptions that persists across incremental builds. Stores
+ * metadata in a location outside of {@code CLASS_OUTPUT} so that Gradle's incremental
+ * compilation does not delete it.
+ *
+ * @author Agustin Palazzo
+ * @see ConfigurationMetadataAnnotationProcessor
+ */
+class DescriptionCache {
+
+	private final File cacheFile;
+
+	private ConfigurationMetadata cachedMetadata;
+
+	DescriptionCache(String cacheFilePath) {
+		this.cacheFile = new File(cacheFilePath);
+		this.cachedMetadata = read();
+	}
+
+	/**
+	 * Look up a cached description for the given property name.
+	 * @param propertyName the fully qualified property name
+	 * @return the cached description or {@code null}
+	 */
+	String getDescription(String propertyName) {
+		if (this.cachedMetadata == null) {
+			return null;
+		}
+		for (ItemMetadata item : this.cachedMetadata.getItems()) {
+			if (item.isOfItemType(ItemMetadata.ItemType.PROPERTY) && propertyName.equals(item.getName())) {
+				return item.getDescription();
+			}
+		}
+		return null;
+	}
+
+	/**
+	 * Replace the cache with the given metadata. After
+	 * {@link ConfigurationMetadataAnnotationProcessor#fillCachedDescriptions} has
+	 * restored descriptions from the cache, the metadata is the complete picture of the
+	 * current build. Replacing (instead of merging) ensures that entries for deleted or
+	 * de-annotated types are automatically pruned.
+	 * @param metadata the current build's metadata with descriptions already filled
+	 */
+	void update(ConfigurationMetadata metadata) {
+		write(metadata);
+		this.cachedMetadata = new ConfigurationMetadata(metadata);
+	}
+
+	private ConfigurationMetadata read() {
+		if (!this.cacheFile.exists()) {
+			return null;
+		}
+		try (FileInputStream in = new FileInputStream(this.cacheFile)) {
+			return new JsonMarshaller().read(in);
+		}
+		catch (Exception ex) {
+			return null;
+		}
+	}
+
+	private void write(ConfigurationMetadata metadata) {
+		this.cacheFile.getParentFile().mkdirs();
+		try (FileOutputStream out = new FileOutputStream(this.cacheFile)) {
+			new JsonMarshaller().write(metadata, out);
+		}
+		catch (IOException ex) {
+			// Cache write failure is non-fatal
+		}
+	}
+
+}

configuration-metadata/spring-boot-configuration-processor/src/main/java/org/springframework/boot/configurationprocessor/MetadataGenerationEnvironment.java

@@ -137,6 +137,10 @@ class MetadataGenerationEnvironment {
 		return this.typeUtils;
 	}
 
+	boolean hasSourceTree(TypeElement element) {
+		return this.fieldValuesParser.hasSourceTree(element);
+	}
+
 	Messager getMessager() {
 		return this.messager;
 	}

configuration-metadata/spring-boot-configuration-processor/src/main/java/org/springframework/boot/configurationprocessor/fieldvalues/FieldValuesParser.java

@@ -30,13 +30,19 @@ import org.springframework.boot.configurationprocessor.fieldvalues.javac.JavaCom
  * @since 1.1.2
  * @see JavaCompilerFieldValuesParser
  */
-@FunctionalInterface
 public interface FieldValuesParser {
 
 	/**
 	 * Implementation of {@link FieldValuesParser} that always returns an empty result.
 	 */
-	FieldValuesParser NONE = (element) -> Collections.emptyMap();
+	FieldValuesParser NONE = new FieldValuesParser() {
+
+		@Override
+		public Map<String, Object> getFieldValues(TypeElement element) {
+			return Collections.emptyMap();
+		}
+
+	};
 
 	/**
 	 * Return the field values for the given element.
@@ -46,4 +52,16 @@ public interface FieldValuesParser {
 	 */
 	Map<String, Object> getFieldValues(TypeElement element) throws Exception;
 
+	/**
+	 * Return whether the given element has a source tree available. Elements loaded from
+	 * {@code .class} files during incremental compilation will not have a source tree,
+	 * meaning javadoc comments are unavailable.
+	 * @param element the element to check
+	 * @return {@code true} if the element has source, {@code false} if backed by
+	 * {@code .class}
+	 */
+	default boolean hasSourceTree(TypeElement element) {
+		return true;
+	}
+
 }

configuration-metadata/spring-boot-configuration-processor/src/main/java/org/springframework/boot/configurationprocessor/fieldvalues/javac/JavaCompilerFieldValuesParser.java

@@ -57,6 +57,16 @@ public class JavaCompilerFieldValuesParser implements FieldValuesParser {
 		return Collections.emptyMap();
 	}
 
+	@Override
+	public boolean hasSourceTree(TypeElement element) {
+		try {
+			return this.trees.getTree(element) != null;
+		}
+		catch (Exception ex) {
+			return true;
+		}
+	}
+
 	/**
 	 * {@link TreeVisitor} to collect fields.
 	 */

configuration-metadata/spring-boot-configuration-processor/src/test/java/org/springframework/boot/configurationprocessor/DescriptionCacheTests.java

@@ -0,0 +1,292 @@
+/*
+ * Copyright 2012-present 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.boot.configurationprocessor;
+
+import java.io.File;
+import java.io.IOException;
+import java.io.InputStream;
+import java.net.URI;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.util.Arrays;
+import java.util.Collections;
+import java.util.List;
+
+import javax.tools.JavaCompiler;
+import javax.tools.JavaFileObject;
+import javax.tools.SimpleJavaFileObject;
+import javax.tools.StandardJavaFileManager;
+import javax.tools.StandardLocation;
+import javax.tools.ToolProvider;
+
+import org.junit.jupiter.api.Test;
+import org.junit.jupiter.api.io.TempDir;
+
+import org.springframework.boot.configurationprocessor.metadata.ConfigurationMetadata;
+import org.springframework.boot.configurationprocessor.metadata.ItemMetadata;
+import org.springframework.boot.configurationprocessor.metadata.JsonMarshaller;
+import org.springframework.boot.configurationprocessor.test.TestConfigurationMetadataAnnotationProcessor;
+import org.springframework.boot.configurationsample.incremental.BarProperties;
+import org.springframework.boot.configurationsample.incremental.FooProperties;
+import org.springframework.boot.configurationsample.record.ExampleRecord;
+import org.springframework.core.test.tools.SourceFile;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * Tests for {@link DescriptionCache} verifying that property descriptions survive
+ * Gradle-style incremental compilation where unchanged types arrive as {@code .class}
+ * files (without javadoc).
+ *
+ * @author Agustin Palazzo
+ */
+class DescriptionCacheTests {
+
+	private static final String METADATA_PATH = "META-INF/spring-configuration-metadata.json";
+
+	@Test
+	void incrementalBuildWithoutCacheLosesDescription(@TempDir Path tempDir) throws Exception {
+		Path classOutput = tempDir.resolve("classes");
+		Path sourceOutput = tempDir.resolve("sources");
+		Files.createDirectories(classOutput);
+		Files.createDirectories(sourceOutput);
+
+		String classpath = System.getProperty("java.class.path");
+		String fooSource = SourceFile.forTestClass(FooProperties.class).getContent();
+		String barSource = SourceFile.forTestClass(BarProperties.class).getContent();
+
+		List<JavaFileObject> allSources = List.of(
+				inMemorySource("org.springframework.boot.configurationsample.incremental.FooProperties", fooSource),
+				inMemorySource("org.springframework.boot.configurationsample.incremental.BarProperties", barSource));
+
+		boolean ok = compile(classOutput, sourceOutput, classpath, null, allSources, null);
+		assertThat(ok).as("Full compilation").isTrue();
+		assertThat(descriptionOf(readMetadata(classOutput), "foo.counter")).isEqualTo("A nice counter description.");
+		assertThat(descriptionOf(readMetadata(classOutput), "bar.counter")).isEqualTo("A nice counter description.");
+
+		Files.deleteIfExists(classOutput.resolve(METADATA_PATH));
+
+		String incrementalCp = classpath + File.pathSeparator + classOutput;
+		List<JavaFileObject> barOnly = List.of(
+				inMemorySource("org.springframework.boot.configurationsample.incremental.BarProperties", barSource));
+		List<String> fooAsClass = List
+			.of("org.springframework.boot.configurationsample.incremental.FooProperties");
+
+		ok = compile(classOutput, sourceOutput, incrementalCp, null, barOnly, fooAsClass);
+		assertThat(ok).as("Incremental compilation").isTrue();
+
+		ConfigurationMetadata incremental = readMetadata(classOutput);
+		assertThat(descriptionOf(incremental, "bar.counter")).isEqualTo("A nice counter description.");
+		assertThat(descriptionOf(incremental, "foo.counter")).as("BUG: description lost without cache").isNull();
+	}
+
+	@Test
+	void incrementalBuildWithCachePreservesDescription(@TempDir Path tempDir) throws Exception {
+		Path classOutput = tempDir.resolve("classes");
+		Path sourceOutput = tempDir.resolve("sources");
+		Path cacheFile = tempDir.resolve("description-cache.json");
+		Files.createDirectories(classOutput);
+		Files.createDirectories(sourceOutput);
+
+		String classpath = System.getProperty("java.class.path");
+		String fooSource = SourceFile.forTestClass(FooProperties.class).getContent();
+		String barSource = SourceFile.forTestClass(BarProperties.class).getContent();
+
+		List<JavaFileObject> allSources = List.of(
+				inMemorySource("org.springframework.boot.configurationsample.incremental.FooProperties", fooSource),
+				inMemorySource("org.springframework.boot.configurationsample.incremental.BarProperties", barSource));
+
+		boolean ok = compile(classOutput, sourceOutput, classpath, cacheFile, allSources, null);
+		assertThat(ok).as("Full compilation").isTrue();
+		assertThat(descriptionOf(readMetadata(classOutput), "foo.counter")).isEqualTo("A nice counter description.");
+		assertThat(descriptionOf(readMetadata(classOutput), "bar.counter")).isEqualTo("A nice counter description.");
+		assertThat(Files.exists(cacheFile)).as("Cache file created").isTrue();
+
+		Files.deleteIfExists(classOutput.resolve(METADATA_PATH));
+
+		String incrementalCp = classpath + File.pathSeparator + classOutput;
+		List<JavaFileObject> barOnly = List.of(
+				inMemorySource("org.springframework.boot.configurationsample.incremental.BarProperties", barSource));
+		List<String> fooAsClass = List
+			.of("org.springframework.boot.configurationsample.incremental.FooProperties");
+
+		ok = compile(classOutput, sourceOutput, incrementalCp, cacheFile, barOnly, fooAsClass);
+		assertThat(ok).as("Incremental compilation").isTrue();
+
+		ConfigurationMetadata incremental = readMetadata(classOutput);
+		assertThat(descriptionOf(incremental, "bar.counter")).isEqualTo("A nice counter description.");
+		assertThat(descriptionOf(incremental, "foo.counter")).as("Description preserved from cache")
+			.isEqualTo("A nice counter description.");
+	}
+
+	@Test
+	void cacheIsPrunedWhenTypeIsRemoved(@TempDir Path tempDir) throws Exception {
+		Path classOutput = tempDir.resolve("classes");
+		Path sourceOutput = tempDir.resolve("sources");
+		Path cacheFile = tempDir.resolve("description-cache.json");
+		Files.createDirectories(classOutput);
+		Files.createDirectories(sourceOutput);
+
+		String classpath = System.getProperty("java.class.path");
+		String fooSource = SourceFile.forTestClass(FooProperties.class).getContent();
+		String barSource = SourceFile.forTestClass(BarProperties.class).getContent();
+
+		List<JavaFileObject> allSources = List.of(
+				inMemorySource("org.springframework.boot.configurationsample.incremental.FooProperties", fooSource),
+				inMemorySource("org.springframework.boot.configurationsample.incremental.BarProperties", barSource));
+
+		boolean ok = compile(classOutput, sourceOutput, classpath, cacheFile, allSources, null);
+		assertThat(ok).as("Full compilation").isTrue();
+
+		ConfigurationMetadata cache1 = readJson(cacheFile);
+		assertThat(descriptionOf(cache1, "foo.counter")).isEqualTo("A nice counter description.");
+		assertThat(descriptionOf(cache1, "bar.counter")).isEqualTo("A nice counter description.");
+
+		Files.deleteIfExists(classOutput.resolve(METADATA_PATH));
+
+		List<JavaFileObject> barOnly = List.of(
+				inMemorySource("org.springframework.boot.configurationsample.incremental.BarProperties", barSource));
+		ok = compile(classOutput, sourceOutput, classpath, cacheFile, barOnly, null);
+		assertThat(ok).as("Compile without FooProperties").isTrue();
+
+		ConfigurationMetadata cache2 = readJson(cacheFile);
+		assertThat(descriptionOf(cache2, "bar.counter")).isEqualTo("A nice counter description.");
+		assertThat(descriptionOf(cache2, "foo.counter")).as("Pruned from cache").isNull();
+	}
+
+	@Test
+	void incrementalBuildWithCachePreservesRecordDescription(@TempDir Path tempDir) throws Exception {
+		Path classOutput = tempDir.resolve("classes");
+		Path sourceOutput = tempDir.resolve("sources");
+		Path cacheFile = tempDir.resolve("description-cache.json");
+		Files.createDirectories(classOutput);
+		Files.createDirectories(sourceOutput);
+
+		String classpath = System.getProperty("java.class.path");
+		String recordSource = SourceFile.forTestClass(ExampleRecord.class).getContent();
+		String barSource = SourceFile.forTestClass(BarProperties.class).getContent();
+
+		List<JavaFileObject> allSources = List.of(
+				inMemorySource("org.springframework.boot.configurationsample.record.ExampleRecord", recordSource),
+				inMemorySource("org.springframework.boot.configurationsample.incremental.BarProperties", barSource));
+
+		boolean ok = compile(classOutput, sourceOutput, classpath, cacheFile, allSources, null);
+		assertThat(ok).as("Full compilation").isTrue();
+		assertThat(descriptionOf(readMetadata(classOutput), "record.descriptions.some-string"))
+			.isEqualTo("very long description that doesn't fit single line and is indented");
+
+		Files.deleteIfExists(classOutput.resolve(METADATA_PATH));
+
+		String incrementalCp = classpath + File.pathSeparator + classOutput;
+		List<JavaFileObject> barOnly = List.of(
+				inMemorySource("org.springframework.boot.configurationsample.incremental.BarProperties", barSource));
+		List<String> recordAsClass = List
+			.of("org.springframework.boot.configurationsample.record.ExampleRecord");
+
+		ok = compile(classOutput, sourceOutput, incrementalCp, cacheFile, barOnly, recordAsClass);
+		assertThat(ok).as("Incremental compilation").isTrue();
+
+		ConfigurationMetadata incremental = readMetadata(classOutput);
+		assertThat(descriptionOf(incremental, "bar.counter")).isEqualTo("A nice counter description.");
+		assertThat(descriptionOf(incremental, "record.descriptions.some-string"))
+			.as("Record description preserved from cache")
+			.isEqualTo("very long description that doesn't fit single line and is indented");
+	}
+
+	@Test
+	void corruptCacheFileIsIgnored(@TempDir Path tempDir) throws Exception {
+		Path classOutput = tempDir.resolve("classes");
+		Path sourceOutput = tempDir.resolve("sources");
+		Path cacheFile = tempDir.resolve("description-cache.json");
+		Files.createDirectories(classOutput);
+		Files.createDirectories(sourceOutput);
+		Files.writeString(cacheFile, "{ this is not valid json !!!");
+
+		String classpath = System.getProperty("java.class.path");
+		String fooSource = SourceFile.forTestClass(FooProperties.class).getContent();
+
+		List<JavaFileObject> sources = List.of(
+				inMemorySource("org.springframework.boot.configurationsample.incremental.FooProperties", fooSource));
+
+		boolean ok = compile(classOutput, sourceOutput, classpath, cacheFile, sources, null);
+		assertThat(ok).as("Compilation with corrupt cache").isTrue();
+
+		ConfigurationMetadata metadata = readMetadata(classOutput);
+		assertThat(metadata).isNotNull();
+		assertThat(descriptionOf(metadata, "foo.counter")).isEqualTo("A nice counter description.");
+	}
+
+	private boolean compile(Path classOutput, Path sourceOutput, String classpath, Path cacheFile,
+			List<JavaFileObject> sources, List<String> classes) throws IOException {
+		JavaCompiler compiler = ToolProvider.getSystemJavaCompiler();
+		try (StandardJavaFileManager fileManager = compiler.getStandardFileManager(null, null, null)) {
+			fileManager.setLocation(StandardLocation.CLASS_OUTPUT, List.of(classOutput.toFile()));
+			fileManager.setLocation(StandardLocation.SOURCE_OUTPUT, List.of(sourceOutput.toFile()));
+			fileManager.setLocation(StandardLocation.CLASS_PATH, classpathFiles(classpath));
+
+			List<String> options = (cacheFile != null)
+					? List.of("-A" + ConfigurationMetadataAnnotationProcessor.DESCRIPTION_CACHE_LOCATION_OPTION + "="
+							+ cacheFile.toAbsolutePath())
+					: Collections.emptyList();
+
+			JavaCompiler.CompilationTask task = compiler.getTask(null, fileManager, null, options, classes, sources);
+			task.setProcessors(List.of(new TestConfigurationMetadataAnnotationProcessor()));
+			return task.call();
+		}
+	}
+
+	private List<File> classpathFiles(String classpath) {
+		return Arrays.stream(classpath.split(File.pathSeparator)).map(File::new).toList();
+	}
+
+	private ConfigurationMetadata readJson(Path file) throws Exception {
+		if (!Files.exists(file)) {
+			return null;
+		}
+		try (InputStream in = Files.newInputStream(file)) {
+			return new JsonMarshaller().read(in);
+		}
+	}
+
+	private ConfigurationMetadata readMetadata(Path classOutput) throws Exception {
+		return readJson(classOutput.resolve(METADATA_PATH));
+	}
+
+	private String descriptionOf(ConfigurationMetadata metadata, String propertyName) {
+		if (metadata == null) {
+			return null;
+		}
+		return metadata.getItems()
+			.stream()
+			.filter((item) -> item.isOfItemType(ItemMetadata.ItemType.PROPERTY))
+			.filter((item) -> propertyName.equals(item.getName()))
+			.findFirst()
+			.map(ItemMetadata::getDescription)
+			.orElse(null);
+	}
+
+	private JavaFileObject inMemorySource(String className, String content) {
+		URI uri = URI.create("string:///" + className.replace('.', '/') + ".java");
+		return new SimpleJavaFileObject(uri, JavaFileObject.Kind.SOURCE) {
+			@Override
+			public CharSequence getCharContent(boolean ignoreEncodingErrors) {
+				return content;
+			}
+		};
+	}
+
+}