Problem with calling super in overridden default method

Improve the fix from #4727:
- treat default methods like abstract (2 locations)

Fixes #1600

Author: stephan-herrmann

org.eclipse.jdt.core.compiler.batch/src/org/eclipse/jdt/internal/compiler/lookup/Scope.java

@@ -4681,10 +4681,10 @@ protected final MethodBinding mostSpecificMethodBinding(MethodBinding[] visible,
 			receiverType = receiverType instanceof CaptureBinding ? receiverType : (ReferenceBinding) receiverType.erasure();
 
 		// within the boundaries of "chosen arbitrarily among the subset of the maximally specific methods that are preferred"
-		// put concrete methods first, default methods second:
+		// put concrete methods first:
 		Arrays.sort(moreSpecific, (m1, m2) -> {
-			int rank1 = m1 == null ? 3 : m1.isAbstract() ? 2 : m1.isDefaultMethod() ? 1 : 0;
-			int rank2 = m2 == null ? 3 : m2.isAbstract() ? 2 : m2.isDefaultMethod() ? 1 : 0;
+			int rank1 = m1 == null ? 3 : (m1.isAbstract() && !m1.isDefaultMethod()) ? 2 : 0;
+			int rank2 = m2 == null ? 3 : (m2.isAbstract() && !m2.isDefaultMethod()) ? 2 : 0;
 			return rank1 - rank2;
 		});
 		boolean hasConsideredNullContract = false;
@@ -4703,7 +4703,7 @@ protected final MethodBinding mostSpecificMethodBinding(MethodBinding[] visible,
 						if (TypeBinding.equalsEquals(original.declaringClass, original2.declaringClass))
 							break nextSpecific; // duplicates thru substitution
 
-						if (!original.isAbstract()) {
+						if (!original.isAbstract() && !original.isDefaultMethod()) {
 							if (original2.isAbstract() || original2.isDefaultMethod())
 								continue; // only compare current against other concrete methods
 

org.eclipse.jdt.core.tests.compiler/src/org/eclipse/jdt/core/tests/compiler/regression/InterfaceMethodsTest.java

@@ -3312,4 +3312,39 @@ default void setReadOnly(boolean readOnly) {
 			}
 			"""});
 	}
+	public void testGH1600_2() {
+		runConformTest(new String[] {"Test.java",
+			"""
+			interface I0 {
+				default void m() throws Exception {}
+				default Number n() throws Exception { return 0l; }
+			}
+			interface I2 extends I0 {
+				@Override abstract void m() throws Exception;
+				@Override abstract Integer n() throws Exception;
+			}
+			class C2 implements I2 {
+				@Override public Integer n() throws Exception { return 13; }
+				@Override public void m() {}
+			}
+			public class Test {
+				void test1(I0 i) throws Exception {
+					if (i instanceof I2)
+						((I2) i).m();
+					else
+						System.out.print("no");
+				}
+				void test2(I0 i0) throws Exception {
+					Integer i = ((I2) i0).n();
+					System.out.print(i);
+				}
+				public static void main(String... args) throws Exception {
+					Test t = new Test();
+					t.test1(new I0() {});
+					t.test2(new C2());
+				}
+			}
+			"""},
+			"no13");
+	}
 }