Make processor output fully reproducible

Update `AutoConfigureAnnotationProcessor` to ensure that the generated
properties file is fully repeatable. Properties are now sorted and
written out directly to ensure that the timestamp comment is not
present.

Closes gh-19370

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

@@ -17,7 +17,9 @@
 package org.springframework.boot.autoconfigureprocessor;
 
 import java.io.IOException;
-import java.io.OutputStream;
+import java.io.OutputStreamWriter;
+import java.io.Writer;
+import java.nio.charset.StandardCharsets;
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.Collections;
@@ -26,11 +28,12 @@ import java.util.HashSet;
 import java.util.LinkedHashMap;
 import java.util.List;
 import java.util.Map;
-import java.util.Properties;
 import java.util.Set;
+import java.util.TreeMap;
 import java.util.stream.Stream;
 
 import javax.annotation.processing.AbstractProcessor;
+import javax.annotation.processing.Filer;
 import javax.annotation.processing.RoundEnvironment;
 import javax.annotation.processing.SupportedAnnotationTypes;
 import javax.lang.model.SourceVersion;
@@ -66,7 +69,7 @@ public class AutoConfigureAnnotationProcessor extends AbstractProcessor {
 
 	private final Map<String, ValueExtractor> valueExtractors;
 
-	private final Properties properties = new Properties();
+	private final Map<String, String> properties = new TreeMap<>();
 
 	public AutoConfigureAnnotationProcessor() {
 		Map<String, String> annotations = new LinkedHashMap<>();
@@ -177,10 +180,15 @@ public class AutoConfigureAnnotationProcessor extends AbstractProcessor {
 
 	private void writeProperties() throws IOException {
 		if (!this.properties.isEmpty()) {
-			FileObject file = this.processingEnv.getFiler().createResource(StandardLocation.CLASS_OUTPUT, "",
-					PROPERTIES_PATH);
-			try (OutputStream outputStream = file.openOutputStream()) {
-				this.properties.store(outputStream, null);
+			Filer filer = this.processingEnv.getFiler();
+			FileObject file = filer.createResource(StandardLocation.CLASS_OUTPUT, "", PROPERTIES_PATH);
+			try (Writer writer = new OutputStreamWriter(file.openOutputStream(), StandardCharsets.UTF_8)) {
+				for (Map.Entry<String, String> entry : this.properties.entrySet()) {
+					writer.append(entry.getKey());
+					writer.append("=");
+					writer.append(entry.getValue());
+					writer.append(System.lineSeparator());
+				}
 			}
 		}
 	}

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

@@ -25,6 +25,7 @@ import org.junit.jupiter.api.Test;
 import org.junit.jupiter.api.io.TempDir;
 
 import org.springframework.boot.testsupport.compiler.TestCompiler;
+import org.springframework.util.FileCopyUtils;
 
 import static org.assertj.core.api.Assertions.assertThat;
 
@@ -96,11 +97,24 @@ class AutoConfigureAnnotationProcessorTests {
 				"123");
 	}
 
+	@Test // gh-19370
+	void propertiesAreFullRepeatable() throws Exception {
+		String first = new String(
+				FileCopyUtils.copyToByteArray(process(TestOrderedClassConfiguration.class).getWrittenFile()));
+		String second = new String(
+				FileCopyUtils.copyToByteArray(process(TestOrderedClassConfiguration.class).getWrittenFile()));
+		assertThat(first).isEqualTo(second).doesNotContain("#");
+	}
+
 	private Properties compile(Class<?>... types) throws IOException {
+		return process(types).getWrittenProperties();
+	}
+
+	private TestAutoConfigureAnnotationProcessor process(Class<?>... types) {
 		TestAutoConfigureAnnotationProcessor processor = new TestAutoConfigureAnnotationProcessor(
 				this.compiler.getOutputLocation());
 		this.compiler.getTask(types).call(processor);
-		return processor.getWrittenProperties();
+		return processor;
 	}
 
 }

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

@@ -60,7 +60,7 @@ public class TestAutoConfigureAnnotationProcessor extends AutoConfigureAnnotatio
 	}
 
 	public Properties getWrittenProperties() throws IOException {
-		File file = new File(this.outputLocation, PROPERTIES_PATH);
+		File file = getWrittenFile();
 		if (!file.exists()) {
 			return null;
 		}
@@ -71,4 +71,8 @@ public class TestAutoConfigureAnnotationProcessor extends AutoConfigureAnnotatio
 		}
 	}
 
+	public File getWrittenFile() {
+		return new File(this.outputLocation, PROPERTIES_PATH);
+	}
+
 }