GROOVY-11815: STC: retain generics of LUB under an instanceof guard

Author: eric-milles

src/main/java/org/codehaus/groovy/transform/stc/StaticTypeCheckingVisitor.java

@@ -6215,7 +6215,7 @@ private ClassNode getInferredTypeFromTempInfo(final Expression expression, final
                 ClassNode   superclass;
                 ClassNode[] interfaces;
                 if (expressionType instanceof WideningCategories.LowestUpperBoundClassNode) {
-                    superclass = expressionType.getSuperClass();
+                    superclass = expressionType.getUnresolvedSuperClass(); // GROOVY-11815
                     interfaces = expressionType.getInterfaces();
                 } else if (expressionType != null && expressionType.isInterface()) {
                     superclass = OBJECT_TYPE;

src/test/groovy/groovy/transform/stc/TypeInferenceSTCTest.groovy

@@ -127,7 +127,7 @@ class TypeInferenceSTCTest extends StaticTypeCheckingTestCase {
         shouldFailWithMessages '''
             Object o
             if (o instanceof String) {
-               o.toUpperCase()
+                o.toUpperCase()
             } else {
                 o.toUpperCase() // ensure that type information is reset
             }
@@ -297,6 +297,25 @@ class TypeInferenceSTCTest extends StaticTypeCheckingTestCase {
         '''
     }
 
+    // GROOVY-11815
+    void testInstanceOf13() {
+        assertScript '''
+            def c = true ? new ArrayDeque() : new Stack()
+            if (c instanceof Deque) {
+                c.addFirst(1)
+            //  ^ (AbstractCollection<Object> & Serializable & ... & Deque)
+            }
+        '''
+        shouldFailWithMessages '''
+            def c = true ? new ArrayDeque<String>() : new Stack<String>()
+            if (c instanceof Serializable) {
+                c.add(1)
+            //  ^ (AbstractCollection<String> & Serializable & ... & Deque)
+            }
+        ''',
+        'Cannot call <UnionType:java.util.AbstractCollection','#add(java.lang.String) with arguments [int]'
+    }
+
     // GROOVY-5226
     void testNestedInstanceOf1() {
         assertScript '''