fix PY-8909 change method signature doesn't change argument names in function body

python/src/com/jetbrains/python/refactoring/changeSignature/PyChangeInfo.java

@@ -37,6 +37,7 @@ public class PyChangeInfo implements ChangeInfo {
 
     if (oldParameters.length != newParameterInfo.length) {
       myIsParameterSetOrOrderChanged = true;
+      myIsParametersNameChanged = true;
     }
     else {
       myIsParameterSetOrOrderChanged = false;

python/src/com/jetbrains/python/refactoring/changeSignature/PyChangeSignatureUsageProcessor.java

@@ -285,9 +285,11 @@ public class PyChangeSignatureUsageProcessor implements ChangeSignatureUsageProc
       for (int i = 0; i != parameters.length; ++i) {
         PyParameterInfo paramInfo = parameters[i];
         final PyParameter[] oldParameters = function.getParameterList().getParameters();
-        final UsageInfo[] usages = RenameUtil.findUsages(oldParameters[paramInfo.getOldIndex()], paramInfo.getName(), true, false, null);
-        for (UsageInfo info : usages) {
-          RenameUtil.rename(info, paramInfo.getName());
+        if (paramInfo.getOldIndex() >= 0) {
+          final UsageInfo[] usages = RenameUtil.findUsages(oldParameters[paramInfo.getOldIndex()], paramInfo.getName(), true, false, null);
+          for (UsageInfo info : usages) {
+            RenameUtil.rename(info, paramInfo.getName());
+          }
         }
       }
     }

python/testData/refactoring/changeSignature/moveRenameParam.after.py

@@ -0,0 +1,2 @@
+def foo(b, a2=2):
+  a2 += 1

python/testData/refactoring/changeSignature/moveRenameParam.before.py

@@ -0,0 +1,2 @@
+def bar(a=2):
+  a += 1

python/testSrc/com/jetbrains/python/refactoring/changeSignature/PyChangeSignatureTest.java

@@ -122,6 +122,11 @@ public class PyChangeSignatureTest extends PyTestCase {
                                                               new PyParameterInfo(3, "**extra_info", null, false)));
   }
 
+  public void testMoveRenameParam() {
+    doChangeSignatureTest("foo", Arrays.asList(new PyParameterInfo(-1, "b", "1", false),
+                                                              new PyParameterInfo(0, "a2", "2", true)));
+  }
+
   public void testKeywordOnlyMove() {
     doChangeSignatureTest("f", Arrays.asList(new PyParameterInfo(2, "param2", null, false),
                                              new PyParameterInfo(0, "*", null, false),