Fix too many folding regions in anonymous class

Fixes eclipse-jdt#2022

Author: jakub-suliga

org.eclipse.jdt.text.tests/src/org/eclipse/jdt/text/tests/folding/FoldingTest.java

@@ -458,8 +458,6 @@ void x() {							//here should be an annotation
 
 	@Test
 	public void testAnonymousClassDeclarationFolding() throws Exception {
-		// FIXME this test should work for both foldings. See https://github.com/eclipse-jdt/eclipse.jdt.ui/issues/2022
-		assumeTrue("Currently broken for the 'old' folding. See https://github.com/eclipse-jdt/eclipse.jdt.ui/issues/2022", newFoldingActive);
 		String str= """
 				package org.example.test;
 				public class M {

org.eclipse.jdt.ui/ui/org/eclipse/jdt/ui/text/folding/DefaultJavaFoldingStructureProvider.java

@@ -1637,7 +1637,6 @@ protected void computeFoldingStructure(IJavaElement element, FoldingStructureCom
 		boolean collapse= false;
 		boolean collapseCode= true;
 		switch (element.getElementType()) {
-
 			case IJavaElement.IMPORT_CONTAINER:
 				collapse= ctx.collapseImportContainer();
 				includelastLine= true;
@@ -1646,8 +1645,13 @@ protected void computeFoldingStructure(IJavaElement element, FoldingStructureCom
 				collapseCode= isInnerType((IType) element) && !isAnonymousEnum((IType) element);
 				collapse= ctx.collapseInnerTypes() && collapseCode;
 				break;
-			case IJavaElement.METHOD:
 			case IJavaElement.FIELD:
+				if (containsAnonymousChild(element)) {
+					return;
+				}
+				collapse= ctx.collapseMembers();
+				break;
+			case IJavaElement.METHOD:
 			case IJavaElement.INITIALIZER:
 				collapse= ctx.collapseMembers();
 				break;
@@ -1696,6 +1700,23 @@ protected void computeFoldingStructure(IJavaElement element, FoldingStructureCom
 		}
 	}
 
+	private boolean containsAnonymousChild(IJavaElement element) {
+		if (!(element instanceof IParent parent)) {
+			return false;
+		}
+
+		try {
+			for (IJavaElement child : parent.getChildren()) {
+				if (child instanceof IType t && t.isAnonymous()) {
+					return true;
+				}
+			}
+		} catch (JavaModelException e) {
+			JavaPlugin.log(e);
+		}
+		return false;
+	}
+
 	/**
 	 * Returns <code>true</code> if <code>type</code> is an anonymous enum declaration,
 	 * <code>false</code> otherwise. See also https://bugs.eclipse.org/bugs/show_bug.cgi?id=143276