change signature: add warning if new signature duplicates method in overrider (IDEA-157659)

java/java-tests/testData/refactoring/changeSignature/DuplicatedSignatureInInheritor.java

@@ -0,0 +1,8 @@
+class A {
+  void fo<caret>o() {}
+}
+
+class B extends A {
+  void foo() {}
+  void foo(int i) {}
+}

java/java-tests/testSrc/com/intellij/refactoring/ChangeSignatureTest.java

@@ -60,6 +60,14 @@ public class ChangeSignatureTest extends ChangeSignatureBaseTest {
     catch (BaseRefactoringProcessor.ConflictsInTestsException ignored) { }
   }
 
+  public void testDuplicatedSignatureInInheritor() throws Exception {
+    try {
+      doTest(null, new ParameterInfoImpl[] {new ParameterInfoImpl(-1, "i", PsiType.INT)}, true);
+      fail("Conflict expected");
+    }
+    catch (BaseRefactoringProcessor.ConflictsInTestsException ignored) { }
+  }
+
   public void testGenericTypes() {
     doTest(null, null, "T", method -> new ParameterInfoImpl[]{
       new ParameterInfoImpl(-1, "x", myFactory.createTypeFromText("T", method.getParameterList()), "null"),