Fix crashes when cyclic inheritance

More complex situation.
Base class is a template and derived class is a template.

Task-number: QTCREATORBUG-8072
Task-number: QTCREATORBUG-7962
Change-Id: I7e8aa727fccd2bd4a779e6fe781553cd12196682
Reviewed-by: Erik Verbruggen <erik.verbruggen@digia.com>

src/libs/cplusplus/LookupContext.h

@@ -58,7 +58,15 @@ public:
     }
     bool contains(const T *item)
     {
-        return _container.contains(item);
+        if (_container.contains(item))
+            return true;
+
+        foreach (const T *existingItem, _container) {
+            if (existingItem->isEqualTo(item))
+                return true;
+        }
+
+        return false;
     }
 
     void clear(const T *item)

src/plugins/cpptools/cppcompletion_test.cpp

@@ -930,4 +930,43 @@ void CppToolsPlugin::test_completion_cyclic_inheritance_data()
     QTest::newRow("case: indirect cyclic inheritance with templates")
             << code << completions;
 
+    completions.clear();
+    code = "\n"
+           "namespace NS\n"
+           "{\n"
+           "template <typename T> struct SuperClass\n"
+           "{\n"
+           "    typedef T Type;\n"
+           "    Type super_class_type;\n"
+           "};\n"
+           "}\n"
+           "\n"
+           "template <typename T>\n"
+           "struct Class;\n"
+           "\n"
+           "template <typename T, typename S>\n"
+           "struct ClassRecurse : Class<S>\n"
+           "{\n"
+           "    T class_recurse_t;\n"
+           "    S class_recurse_s;\n"
+           "};\n"
+           "\n"
+           "template <typename T>\n"
+           "struct Class : ClassRecurse< T, typename ::NS::SuperClass<T>::Type >\n"
+           "{\n"
+           "    T class_t;\n"
+           "};\n"
+           "\n"
+           "Class<int> c;\n"
+           "c.\n"
+           "@\n"
+            ;
+    completions.append("Class");
+    completions.append("ClassRecurse");
+    completions.append("class_t");
+    completions.append("class_recurse_s");
+    completions.append("class_recurse_t");
+    QTest::newRow("case: direct cyclic inheritance with templates, more complex situation")
+            << code << completions;
+
 }