java 9: ensure private methods in interfaces do not receive implicit public modifier (IDEA-171089)

java/java-psi-impl/src/com/intellij/psi/impl/source/PsiModifierListImpl.java

@@ -17,7 +17,6 @@ package com.intellij.psi.impl.source;
 
 import com.intellij.codeInsight.AnnotationTargetUtil;
 import com.intellij.lang.ASTNode;
-import com.intellij.openapi.util.Condition;
 import com.intellij.psi.*;
 import com.intellij.psi.augment.PsiAugmentProvider;
 import com.intellij.psi.impl.CheckUtil;
@@ -158,9 +157,11 @@ public class PsiModifierListImpl extends JavaStubPsiElement<PsiModifierListStub>
     else if (parent instanceof PsiMethod) {
       PsiClass aClass = ((PsiMethod)parent).getContainingClass();
       if (aClass != null && aClass.isInterface()) {
-        implicitModifiers.add(PUBLIC);
-        if (!explicitModifiers.contains(DEFAULT) && !explicitModifiers.contains(STATIC) && !explicitModifiers.contains(PRIVATE)) {
-          implicitModifiers.add(ABSTRACT);
+        if (!explicitModifiers.contains(PRIVATE)) {
+          implicitModifiers.add(PUBLIC);
+          if (!explicitModifiers.contains(DEFAULT) && !explicitModifiers.contains(STATIC)) {
+            implicitModifiers.add(ABSTRACT);
+          }
         }
       }
       else if (aClass != null && aClass.isEnum() && ((PsiMethod)parent).isConstructor()) {

java/java-tests/testData/codeInsight/daemonCodeAnalyzer/advHighlighting9/PrivateInInterfacesOverriding.java

@@ -0,0 +1,25 @@
+interface A {
+  void m();
+}
+interface A1 extends A {
+  <error descr="Static method 'm()' in 'A1' cannot override instance method 'm()' in 'A'">private static void m()</error> {}
+}
+interface A2 extends A {
+  <error descr="'m()' in 'A2' clashes with 'm()' in 'A'; attempting to assign weaker access privileges ('private'); was 'public'">private</error> void m() {}
+}
+
+interface B {
+  private void m() {}
+}
+interface B1 extends B {
+  private void m() {}
+}
+interface B2 extends B {
+  private static void m() {}
+}
+interface B3 extends B {
+  default void m() {}
+}
+interface B4 extends B {
+  void m();
+}

java/java-tests/testSrc/com/intellij/codeInsight/daemon/LightAdvHighlightingJdk9Test.java

@@ -41,6 +41,7 @@ public class LightAdvHighlightingJdk9Test extends LightDaemonAnalyzerTestCase {
 
   public void testSafeVarargsApplicability() { doTest(true, false); }
   public void testPrivateInInterfaces() { doTest(false, false); }
+  public void testPrivateInInterfacesOverriding() { doTest(false, false); }
   public void testUnderscore() { doTest(false, false); }
   public void testTryWithResources() { doTest(false, false); }