8345773: Class-File API debug printing capability

Reviewed-by: liach
Backport-of: f88c1c6

Author: asotona

src/java.base/share/classes/java/lang/classfile/CompoundElement.java

@@ -34,6 +34,8 @@
 import java.util.stream.Stream;
 import java.util.stream.StreamSupport;
 
+import jdk.internal.classfile.components.ClassPrinter;
+
 /**
  * A {@link ClassFileElement} that has complex structure defined in terms of
  * other classfile elements, such as a method, field, method body, or entire
@@ -92,4 +94,14 @@ public void accept(E e) {
         return Collections.unmodifiableList(list);
     }
 
+    /**
+     * {@return a text representation of the compound element and its contents for debugging purposes}
+     *
+     * The format, structure and exact contents of the returned string are not specified and may change at any time in the future.
+     */
+    default String toDebugString() {
+        StringBuilder text = new StringBuilder();
+        ClassPrinter.toYaml(this, ClassPrinter.Verbosity.TRACE_ALL, text::append);
+        return text.toString();
+    }
 }

test/jdk/jdk/classfile/ClassPrinterTest.java

@@ -23,7 +23,7 @@
 
 /*
  * @test
- * @bug 8335927
+ * @bug 8335927 8345773
  * @summary Testing ClassFile ClassPrinter.
  * @run junit ClassPrinterTest
  */
@@ -122,8 +122,7 @@ ClassModel getClassModel() {
 
     @Test
     void testPrintYamlTraceAll() throws IOException {
-        var out = new StringBuilder();
-        ClassPrinter.toYaml(getClassModel(), ClassPrinter.Verbosity.TRACE_ALL, out::append);
+        var out = getClassModel().toDebugString();
         assertOut(out,
                 """
                   - class name: Foo
@@ -904,7 +903,7 @@ void testWalkMembersOnly() throws IOException {
         assertEquals(node.walk().count(), 42);
     }
 
-    private static void assertOut(StringBuilder out, String expected) {
+    private static void assertOut(CharSequence out, String expected) {
 //        System.out.println("-----------------");
 //        System.out.println(out.toString());
 //        System.out.println("-----------------");