!is supported in data flow info for ifs

idea/src/org/jetbrains/jet/lang/types/JetTypeInferrer.java

@@ -1570,7 +1570,7 @@ public class JetTypeInferrer {
             condition.accept(new JetVisitor() {
                 @Override
                 public void visitIsExpression(JetIsExpression expression) {
-                    if (conditionValue) {
+                    if (conditionValue && !expression.isNegated() || !conditionValue && expression.isNegated()) {
                         JetPattern pattern = expression.getPattern();
                         result[0] = patternsToDataFlowInfo.get(pattern);
                         if (scopeToExtend != null) {

idea/testData/checker/infos/Autocasts.jet

@@ -147,3 +147,9 @@ fun f15(a : A?) {
   <info descr="Automatically cast to B">a</info>.bar()
   <error>c</error>.bar()
 }
+
+fun getStringLength(obj : Any) : Char? {
+  if (obj !is String)
+    return null
+  return <info>obj</info>.get(0) // no cast to String is needed
+}