Fix TestDataFormatterLibcxxListLoop.py test

[teemperor]

Summary

The compilation of the TestDataFormatterLibcxxListLoop.py currently fails with this error:

functionalities/data-formatter/data-formatter-stl/libcxx/list/loop/main.cpp:19:24: error: no member named '__value_' in 'std::__1::__list_node_base<int, void *>'
    assert(third_elem->__value_ == 3);
           ~~~~~~~~~~  ^

It seems the internal structure of list has changed with the 3.8 release. This patch makes the test compile with the current libc++ and with the previous libc++.

[labath]

The slight problem here is that we don't know which libc++ version we are going to build with, so this will then fail for people still using the old one. However, choosing the latest libc++ version here seems like the right thing to do.

The background here is that we don't have a good way of testing that our pretty-printers behave sensibly when the structures they are interpreting get corrupted. This test was my attempt at improving that situation, but it's not without its shortfalls.

The other thing I tried a while back when writing the std::tuple formatter was to re-create a faithful mock of the class in the test. The advantage there would be that we are not tied to the libc++ version, and we would be even able to test formatting of different versions simultaneously. However, writing the mock proved to be so tedious, that I just gave up on the idea.

[teemperor]

We could also check the libc++ version via _LIBCPP_VERSION and just keep the old code around behind an ifdef?

[labath]

Yeah, that sounds like a good interim solution.

[teemperor]

• Added #ifdef for 3.8 release.

[shafik]

Thanks for fixing this.

lldb/packages/Python/lldbsuite/test/functionalities/data-formatter/data-formatter-stl/libcxx/list/loop/main.cpp

 typedef std::list<int> int_list;
 
 int main()
 {
 #ifdef LLDB_USING_LIBCPP
     int_list *numbers_list = new int_list{1,2,3,4,5,6,7,8,9,10};
 
     printf("// Set break point at this line.");
+
+#if _LIBCPP_VERSION >= 3800
+    auto *third_elem = numbers_list->__end_.__next_->__next_->__next_;
+    assert(third_elem->__as_node()->__value_ == 3);
+    auto *fifth_elem = third_elem->__next_->__next_;
+    assert(fifth_elem->__as_node()->__value_ == 5);
+#else
     auto *third_elem = numbers_list->__end_.__next_->__next_->__next_;
     assert(third_elem->__value_ == 3);
     auto *fifth_elem = third_elem->__next_->__next_;
     assert(fifth_elem->__value_ == 5);
+#endif
     fifth_elem->__next_ = third_elem;
 #endif
 
     // Any attempt to free the list will probably crash the program. Let's just leak it.
     return 0; // Set second break point at this line.
 }