C++: fix crash during code completion with base template class

ResolveExpression has to have a reference of ContextLookup. If not there
will be a crash because of deleted instanitated base template class.

Task-number: QTCREATORBUG-9329
Change-Id: I7f8c83da0d81ac6311e76d15a897adbc70b08d75
Reviewed-by: Erik Verbruggen <erik.verbruggen@digia.com>

src/libs/cplusplus/ResolveExpression.h

@@ -122,7 +122,7 @@ protected:
 
 private:
     Scope *_scope;
-    LookupContext _context;
+    const LookupContext& _context;
     Bind bind;
     QList<LookupItem> _results;
     bool _reference;

src/plugins/cpptools/cppcompletion_test.cpp

@@ -1798,3 +1798,37 @@ void CppToolsPlugin::test_completion_namespace_alias_with_many_namespace_declara
     QVERIFY(completions.contains(QLatin1String("Foo1")));
     QVERIFY(completions.contains(QLatin1String("Foo2")));
 }
+
+void CppToolsPlugin::test_completion_crash_cloning_template_class_QTCREATORBUG9329()
+{
+    TestData data;
+    data.srcText =
+            "struct A {};\n"
+            "template <typename T>\n"
+            "struct Templ {};\n"
+            "struct B : A, Templ<A>\n"
+            "{\n"
+            "   int f()\n"
+            "   {\n"
+            "       @\n"
+            "       // padding so we get the scope right\n"
+            "   }\n"
+            "};\n"
+            ;
+    setup(&data);
+
+    Utils::ChangeSet change;
+    QString txt = QLatin1String("this->");
+    change.insert(data.pos, txt);
+    QTextCursor cursor(data.doc);
+    change.apply(&cursor);
+    data.pos += txt.length();
+
+    QStringList completions = getCompletions(data);
+
+    QCOMPARE(completions.size(), 4);
+    QVERIFY(completions.contains(QLatin1String("A")));
+    QVERIFY(completions.contains(QLatin1String("B")));
+    QVERIFY(completions.contains(QLatin1String("Templ")));
+    QVERIFY(completions.contains(QLatin1String("f")));
+}

src/plugins/cpptools/cpptoolsplugin.h

@@ -127,6 +127,7 @@ private slots:
     void test_completion_typedef_using_templates1();
     void test_completion_typedef_using_templates2();
     void test_completion_namespace_alias_with_many_namespace_declarations();
+    void test_completion_crash_cloning_template_class_QTCREATORBUG9329();
 
     void test_format_pointerdeclaration_in_simpledeclarations();
     void test_format_pointerdeclaration_in_simpledeclarations_data();