change signature: show conflicts if delegated method has same erasure as initial one (IDEA-157672)

java/java-impl/src/com/intellij/refactoring/changeSignature/JavaChangeSignatureUsageProcessor.java

@@ -1002,7 +1002,7 @@ public class JavaChangeSignatureUsageProcessor implements ChangeSignatureUsagePr
           LOG.error(e);
         }
       }
-      
+
       checkContract(conflictDescriptions, myChangeInfo.getMethod());
 
       for (UsageInfo usageInfo : usagesSet) {
@@ -1104,7 +1104,7 @@ public class JavaChangeSignatureUsageProcessor implements ChangeSignatureUsagePr
           prototype.getParameterList().add(param);
         }
 
-        ConflictsUtil.checkMethodConflicts(method.getContainingClass(), method, prototype, conflicts);
+        ConflictsUtil.checkMethodConflicts(method.getContainingClass(), myChangeInfo.isGenerateDelegate() ? null : method, prototype, conflicts);
       }
       catch (IncorrectOperationException e) {
         LOG.error(e);

java/java-impl/src/com/intellij/refactoring/util/ConflictsUtil.java

@@ -53,7 +53,7 @@ public class ConflictsUtil {
   }
 
   public static void checkMethodConflicts(@Nullable PsiClass aClass,
-                                          PsiMethod refactoredMethod,
+                                          @Nullable PsiMethod refactoredMethod,
                                           final PsiMethod prototype,
                                           final MultiMap<PsiElement,String> conflicts) {
     if (prototype == null) return;

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

@@ -0,0 +1,3 @@
+class A {
+  void <caret>m() {}
+}

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

@@ -52,6 +52,14 @@ public class ChangeSignatureTest extends ChangeSignatureBaseTest {
     catch (BaseRefactoringProcessor.ConflictsInTestsException ignored) { }
   }
 
+  public void testDelegateWithoutChangesWarnAboutSameMethodInClass() throws Exception {
+    try {
+      doTest(null, new ParameterInfoImpl[0], 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"),