Use YAML compatible classpath.idx format

Update the `classpath.idx` format to align with `layers.idx` and allow
third-parties can parse it as YAML

Closes gh-20861

spring-boot-project/spring-boot-tools/spring-boot-gradle-plugin/src/main/java/org/springframework/boot/gradle/tasks/bundling/BootZipCopyAction.java

@@ -26,9 +26,11 @@ import java.time.OffsetDateTime;
 import java.time.ZoneOffset;
 import java.util.Collection;
 import java.util.LinkedHashSet;
+import java.util.List;
 import java.util.Map;
 import java.util.Set;
 import java.util.function.Function;
+import java.util.stream.Collectors;
 import java.util.zip.CRC32;
 
 import org.apache.commons.compress.archivers.zip.UnixStat;
@@ -345,8 +347,9 @@ class BootZipCopyAction implements CopyAction {
 			Attributes manifestAttributes = BootZipCopyAction.this.manifest.getAttributes();
 			String classPathIndex = (String) manifestAttributes.get("Spring-Boot-Classpath-Index");
 			if (classPathIndex != null) {
-				writeEntry(classPathIndex,
-						ZipEntryWriter.fromLines(BootZipCopyAction.this.encoding, this.writtenLibraries), true);
+				List<String> lines = this.writtenLibraries.stream().map((line) -> "- \"" + line + "\"")
+						.collect(Collectors.toList());
+				writeEntry(classPathIndex, ZipEntryWriter.fromLines(BootZipCopyAction.this.encoding, lines), true);
 			}
 		}
 

spring-boot-project/spring-boot-tools/spring-boot-gradle-plugin/src/test/java/org/springframework/boot/gradle/tasks/bundling/BootJarTests.java

@@ -185,8 +185,8 @@ class BootJarTests extends AbstractBootArchiveTests<TestBootJar> {
 	@Test
 	void whenJarIsLayeredClasspathIndexPointsToLayeredLibs() throws IOException {
 		try (JarFile jarFile = new JarFile(createLayeredJar())) {
-			assertThat(entryLines(jarFile, "BOOT-INF/classpath.idx")).containsExactly("first-library.jar",
-					"second-library.jar", "third-library-SNAPSHOT.jar");
+			assertThat(entryLines(jarFile, "BOOT-INF/classpath.idx")).containsExactly("- \"first-library.jar\"",
+					"- \"second-library.jar\"", "- \"third-library-SNAPSHOT.jar\"");
 		}
 	}
 
@@ -208,8 +208,8 @@ class BootJarTests extends AbstractBootArchiveTests<TestBootJar> {
 		try (JarFile jarFile = new JarFile(createPopulatedJar())) {
 			assertThat(jarFile.getManifest().getMainAttributes().getValue("Spring-Boot-Classpath-Index"))
 					.isEqualTo("BOOT-INF/classpath.idx");
-			assertThat(entryLines(jarFile, "BOOT-INF/classpath.idx")).containsExactly("first-library.jar",
-					"second-library.jar", "third-library-SNAPSHOT.jar");
+			assertThat(entryLines(jarFile, "BOOT-INF/classpath.idx")).containsExactly("- \"first-library.jar\"",
+					"- \"second-library.jar\"", "- \"third-library-SNAPSHOT.jar\"");
 		}
 	}
 

spring-boot-project/spring-boot-tools/spring-boot-loader-tools/src/main/java/org/springframework/boot/loader/tools/Packager.java

@@ -505,7 +505,8 @@ public abstract class Packager {
 		}
 
 		private void writeClasspathIndex(RepackagingLayout layout, AbstractJarWriter writer) throws IOException {
-			List<String> names = this.libraries.keySet().stream().map(this::getJarName).collect(Collectors.toList());
+			List<String> names = this.libraries.keySet().stream().map(this::getJarName)
+					.map((name) -> "- \"" + name + "\"").collect(Collectors.toList());
 			writer.writeIndexFile(layout.getClasspathIndexFileLocation(), names);
 		}
 

spring-boot-project/spring-boot-tools/spring-boot-loader-tools/src/test/java/org/springframework/boot/loader/tools/AbstractPackagerTests.java

@@ -212,7 +212,7 @@ abstract class AbstractPackagerTests<P extends Packager> {
 	}
 
 	@Test
-	void index() throws Exception {
+	void classPathIndex() throws Exception {
 		TestJarFile libJar1 = new TestJarFile(this.tempDir);
 		libJar1.addClass("a/b/C.class", ClassWithoutMainMethod.class, JAN_1_1985);
 		File libJarFile1 = libJar1.getFile();
@@ -233,8 +233,9 @@ abstract class AbstractPackagerTests<P extends Packager> {
 		assertThat(hasPackagedEntry("BOOT-INF/classpath.idx")).isTrue();
 		String index = getPackagedEntryContent("BOOT-INF/classpath.idx");
 		String[] libraries = index.split("\\r?\\n");
-		assertThat(Arrays.asList(libraries)).contains(libJarFile1.getName(), libJarFile2.getName(),
-				libJarFile3.getName());
+		List<String> expected = Stream.of(libJarFile1, libJarFile2, libJarFile3)
+				.map((jar) -> "- \"" + jar.getName() + "\"").collect(Collectors.toList());
+		assertThat(Arrays.asList(libraries)).containsExactlyElementsOf(expected);
 	}
 
 	@Test
@@ -263,8 +264,9 @@ abstract class AbstractPackagerTests<P extends Packager> {
 		});
 		assertThat(hasPackagedEntry("BOOT-INF/classpath.idx")).isTrue();
 		String classpathIndex = getPackagedEntryContent("BOOT-INF/classpath.idx");
-		assertThat(Arrays.asList(classpathIndex.split("\\n"))).containsExactly(libJarFile1.getName(),
-				libJarFile2.getName(), libJarFile3.getName());
+		List<String> expectedClasspathIndex = Stream.of(libJarFile1, libJarFile2, libJarFile3)
+				.map((file) -> "- \"" + file.getName() + "\"").collect(Collectors.toList());
+		assertThat(Arrays.asList(classpathIndex.split("\\n"))).containsExactlyElementsOf(expectedClasspathIndex);
 		assertThat(hasPackagedEntry("BOOT-INF/layers.idx")).isTrue();
 		String layersIndex = getPackagedEntryContent("BOOT-INF/layers.idx");
 		List<String> expectedLayers = new ArrayList<>();
@@ -293,7 +295,8 @@ abstract class AbstractPackagerTests<P extends Packager> {
 		execute(packager, Libraries.NONE);
 		assertThat(hasPackagedEntry("BOOT-INF/classpath.idx")).isTrue();
 		String classpathIndex = getPackagedEntryContent("BOOT-INF/classpath.idx");
-		assertThat(Arrays.asList(classpathIndex.split("\\n"))).containsExactly("spring-boot-jarmode-layertools.jar");
+		assertThat(Arrays.asList(classpathIndex.split("\\n")))
+				.containsExactly("- \"spring-boot-jarmode-layertools.jar\"");
 		assertThat(hasPackagedEntry("BOOT-INF/layers.idx")).isTrue();
 		String layersIndex = getPackagedEntryContent("BOOT-INF/layers.idx");
 		List<String> expectedLayers = new ArrayList<>();

spring-boot-project/spring-boot-tools/spring-boot-loader/src/main/java/org/springframework/boot/loader/ClassPathIndexFile.java

@@ -31,6 +31,8 @@ import java.util.Collections;
 import java.util.List;
 import java.util.stream.Collectors;
 
+import org.springframework.util.Assert;
+
 /**
  * A class path index file that provides ordering information for JARs.
  *
@@ -45,7 +47,12 @@ final class ClassPathIndexFile {
 
 	private ClassPathIndexFile(File root, List<String> lines) {
 		this.root = root;
-		this.lines = lines;
+		this.lines = lines.stream().map(this::extractName).collect(Collectors.toList());
+	}
+
+	private String extractName(String line) {
+		Assert.state(line.startsWith("- \"") && line.endsWith("\""), "Malformed classpath index line [" + line + "]");
+		return line.substring(3, line.length() - 1);
 	}
 
 	int size() {

spring-boot-project/spring-boot-tools/spring-boot-loader/src/test/java/org/springframework/boot/loader/AbstractExecutableArchiveLauncherTests.java

@@ -68,9 +68,9 @@ public abstract class AbstractExecutableArchiveLauncherTests {
 			JarEntry indexEntry = new JarEntry(entryPrefix + "/classpath.idx");
 			jarOutputStream.putNextEntry(indexEntry);
 			Writer writer = new OutputStreamWriter(jarOutputStream, StandardCharsets.UTF_8);
-			writer.write("BOOT-INF/lib/foo.jar\n");
-			writer.write("BOOT-INF/lib/bar.jar\n");
-			writer.write("BOOT-INF/lib/baz.jar\n");
+			writer.write("- \"BOOT-INF/lib/foo.jar\"\n");
+			writer.write("- \"BOOT-INF/lib/bar.jar\"\n");
+			writer.write("- \"BOOT-INF/lib/baz.jar\"\n");
 			writer.flush();
 		}
 		addNestedJars(entryPrefix, "/lib/foo.jar", jarOutputStream);

spring-boot-project/spring-boot-tools/spring-boot-loader/src/test/resources/org/springframework/boot/loader/classpath-index-file.idx

-a.jar
-b.jar
-c.jar
-d.jar
-e.jar
+- "a.jar"
+- "b.jar"
+- "c.jar"
+- "d.jar"
+- "e.jar"