Omit empty values for AutoConfigureAfter and AutoConfigureBefore

As @autoConfiguration is now meta-annotated with @AutoConfigureAfter
and @AutoConfigureBefore, the generated property files have a lot of
superfluous lines in the format <class>.AutoConfigureAfter= and
<class>.AutoConfigureBefore=.

One can now configure in the annotation processor for each property key
if empty values should be omitted. This is currently only activated for
AutoConfigureAfter and AutoConfigureBefore

See gh-29907

Author: mhalbritter

spring-boot-project/spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/AutoConfigurationSorterTests.java

@@ -223,8 +223,10 @@ private void addAutoConfigureAfter(Properties properties, String className, Anno
 		Map<String, Object> autoConfigureAfter = annotationMetadata
 				.getAnnotationAttributes(AutoConfigureAfter.class.getName(), true);
 		if (autoConfigureAfter != null) {
-			properties.put(className + ".AutoConfigureAfter",
-					merge((String[]) autoConfigureAfter.get("value"), (String[]) autoConfigureAfter.get("name")));
+			String value = merge((String[]) autoConfigureAfter.get("value"), (String[]) autoConfigureAfter.get("name"));
+			if (!value.isEmpty()) {
+				properties.put(className + ".AutoConfigureAfter", value);
+			}
 		}
 	}
 
@@ -233,8 +235,11 @@ private void addAutoConfigureBefore(Properties properties, String className,
 		Map<String, Object> autoConfigureBefore = annotationMetadata
 				.getAnnotationAttributes(AutoConfigureBefore.class.getName(), true);
 		if (autoConfigureBefore != null) {
-			properties.put(className + ".AutoConfigureBefore",
-					merge((String[]) autoConfigureBefore.get("value"), (String[]) autoConfigureBefore.get("name")));
+			String value = merge((String[]) autoConfigureBefore.get("value"),
+					(String[]) autoConfigureBefore.get("name"));
+			if (!value.isEmpty()) {
+				properties.put(className + ".AutoConfigureBefore", value);
+			}
 		}
 	}
 

spring-boot-project/spring-boot-tools/spring-boot-autoconfigure-processor/src/main/java/org/springframework/boot/autoconfigureprocessor/AutoConfigureAnnotationProcessor.java

@@ -88,11 +88,11 @@ protected List<PropertyGenerator> getPropertyGenerators() {
 		generators.add(PropertyGenerator.of("ConditionalOnWebApplication",
 				"org.springframework.boot.autoconfigure.condition.ConditionalOnWebApplication",
 				ValueExtractor.allFrom("type")));
-		generators.add(PropertyGenerator.of("AutoConfigureBefore",
+		generators.add(PropertyGenerator.of("AutoConfigureBefore", true,
 				"org.springframework.boot.autoconfigure.AutoConfigureBefore", ValueExtractor.allFrom("value", "name"),
 				"org.springframework.boot.autoconfigure.AutoConfiguration",
 				ValueExtractor.allFrom("before", "beforeName")));
-		generators.add(PropertyGenerator.of("AutoConfigureAfter",
+		generators.add(PropertyGenerator.of("AutoConfigureAfter", true,
 				"org.springframework.boot.autoconfigure.AutoConfigureAfter", ValueExtractor.allFrom("value", "name"),
 				"org.springframework.boot.autoconfigure.AutoConfiguration",
 				ValueExtractor.allFrom("after", "afterName")));
@@ -284,13 +284,17 @@ static final class PropertyGenerator {
 
 		private final String keyName;
 
+		private final boolean omitEmptyValues;
+
 		/**
 		 * Maps from annotation class name -> {@link ValueExtractor}.
 		 */
 		private final Map<String, ValueExtractor> valueExtractors;
 
-		private PropertyGenerator(String keyName, Map<String, ValueExtractor> valueExtractors) {
+		private PropertyGenerator(String keyName, boolean omitEmptyValues,
+				Map<String, ValueExtractor> valueExtractors) {
 			this.keyName = keyName;
+			this.omitEmptyValues = omitEmptyValues;
 			this.valueExtractors = valueExtractors;
 		}
 
@@ -303,6 +307,9 @@ ValueExtractor getValueExtractor(String annotation) {
 		}
 
 		void applyToProperties(Map<String, String> properties, String className, List<Object> annotationValues) {
+			if (this.omitEmptyValues && annotationValues.isEmpty()) {
+				return;
+			}
 			mergeProperties(properties, className + "." + this.keyName, toCommaDelimitedString(annotationValues));
 		}
 
@@ -329,15 +336,26 @@ private String toCommaDelimitedString(List<Object> list) {
 		}
 
 		static PropertyGenerator of(String keyName, String annotation, ValueExtractor valueExtractor) {
-			return new PropertyGenerator(keyName, Collections.singletonMap(annotation, valueExtractor));
+			return of(keyName, false, annotation, valueExtractor);
+		}
+
+		static PropertyGenerator of(String keyName, boolean omitEmptyValues, String annotation,
+				ValueExtractor valueExtractor) {
+			return new PropertyGenerator(keyName, omitEmptyValues,
+					Collections.singletonMap(annotation, valueExtractor));
 		}
 
 		static PropertyGenerator of(String keyName, String annotation1, ValueExtractor valueExtractor1,
 				String annotation2, ValueExtractor valueExtractor2) {
+			return of(keyName, false, annotation1, valueExtractor1, annotation2, valueExtractor2);
+		}
+
+		static PropertyGenerator of(String keyName, boolean omitEmptyValues, String annotation1,
+				ValueExtractor valueExtractor1, String annotation2, ValueExtractor valueExtractor2) {
 			Map<String, ValueExtractor> valueExtractors = new LinkedHashMap<>();
 			valueExtractors.put(annotation1, valueExtractor1);
 			valueExtractors.put(annotation2, valueExtractor2);
-			return new PropertyGenerator(keyName, valueExtractors);
+			return new PropertyGenerator(keyName, omitEmptyValues, valueExtractors);
 		}
 
 	}

spring-boot-project/spring-boot-tools/spring-boot-autoconfigure-processor/src/test/java/org/springframework/boot/autoconfigureprocessor/AutoConfigureAnnotationProcessorTests.java

@@ -67,6 +67,19 @@ void annotatedClass() throws Exception {
 				+ "TestClassConfiguration.ConditionalOnWebApplication", "SERVLET");
 	}
 
+	@Test
+	void annotatedClassWithOnlyAutoConfiguration() throws Exception {
+		Properties properties = compile(TestAutoConfigurationOnlyConfiguration.class);
+		assertThat(properties).containsEntry(
+				"org.springframework.boot.autoconfigureprocessor.TestAutoConfigurationOnlyConfiguration", "");
+		assertThat(properties).doesNotContainEntry(
+				"org.springframework.boot.autoconfigureprocessor.TestAutoConfigurationOnlyConfiguration.AutoConfigureAfter",
+				"");
+		assertThat(properties).doesNotContainEntry(
+				"org.springframework.boot.autoconfigureprocessor.TestAutoConfigurationOnlyConfiguration.AutoConfigureBefore",
+				"");
+	}
+
 	@Test
 	void annotatedClassWithOnBeanThatHasName() throws Exception {
 		Properties properties = compile(TestOnBeanWithNameClassConfiguration.class);

spring-boot-project/spring-boot-tools/spring-boot-autoconfigure-processor/src/test/java/org/springframework/boot/autoconfigureprocessor/TestAutoConfigurationConfiguration.java

@@ -26,6 +26,6 @@
  */
 @TestAutoConfiguration(before = InputStream.class, beforeName = { "test.before1", "test.before2" },
 		after = OutputStream.class, afterName = { "test.after1", "test.after2" })
-public class TestAutoConfigurationConfiguration {
+class TestAutoConfigurationConfiguration {
 
 }

spring-boot-project/spring-boot-tools/spring-boot-autoconfigure-processor/src/test/java/org/springframework/boot/autoconfigureprocessor/TestAutoConfigurationOnlyConfiguration.java

@@ -0,0 +1,27 @@
+/*
+ * Copyright 2012-2022 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.boot.autoconfigureprocessor;
+
+/**
+ * Tests a plain {@code @AutoConfiguration} annotated class.
+ *
+ * @author Moritz Halbritter
+ */
+@TestAutoConfiguration
+class TestAutoConfigurationOnlyConfiguration {
+
+}

spring-boot-project/spring-boot-tools/spring-boot-autoconfigure-processor/src/test/java/org/springframework/boot/autoconfigureprocessor/TestAutoConfigureAnnotationProcessor.java

@@ -57,10 +57,10 @@ protected List<PropertyGenerator> getPropertyGenerators() {
 				TestConditionalOnSingleCandidate.class.getName(), new OnBeanConditionValueExtractor()));
 		generators.add(PropertyGenerator.of("ConditionalOnWebApplication",
 				TestConditionalOnWebApplication.class.getName(), ValueExtractor.allFrom("type")));
-		generators.add(PropertyGenerator.of("AutoConfigureBefore", TestAutoConfigureBefore.class.getName(),
+		generators.add(PropertyGenerator.of("AutoConfigureBefore", true, TestAutoConfigureBefore.class.getName(),
 				ValueExtractor.allFrom("value", "name"), TestAutoConfiguration.class.getName(),
 				ValueExtractor.allFrom("before", "beforeName")));
-		generators.add(PropertyGenerator.of("AutoConfigureAfter", TestAutoConfigureAfter.class.getName(),
+		generators.add(PropertyGenerator.of("AutoConfigureAfter", true, TestAutoConfigureAfter.class.getName(),
 				ValueExtractor.allFrom("value", "name"), TestAutoConfiguration.class.getName(),
 				ValueExtractor.allFrom("after", "afterName")));
 		generators.add(PropertyGenerator.of("AutoConfigureOrder", TestAutoConfigureOrder.class.getName(),

spring-boot-project/spring-boot-tools/spring-boot-autoconfigure-processor/src/test/java/org/springframework/boot/autoconfigureprocessor/TestMergedAutoConfigurationConfiguration.java

@@ -31,6 +31,6 @@
 @TestAutoConfigureAfter(value = OutputStream.class, name = { "test.after1", "test.after2" })
 @TestAutoConfiguration(before = ObjectInputStream.class, beforeName = { "test.before3", "test.before4" },
 		after = ObjectOutputStream.class, afterName = { "test.after3", "test.after4" })
-public class TestMergedAutoConfigurationConfiguration {
+class TestMergedAutoConfigurationConfiguration {
 
 }