[libcxx-commits] [libcxx] [libcxx][test-support] Implement fancy_pointer_allocator (PR #196187)

[Nikita Belenkiy via libcxx-commits]

================
@@ -393,21 +394,30 @@ namespace detail {
 template <class T>
 class thread_unsafe_shared_ptr {
 public:
-  thread_unsafe_shared_ptr() = default;
-
-  TEST_CONSTEXPR_CXX14 thread_unsafe_shared_ptr(const thread_unsafe_shared_ptr& other) : block(other.block) {
+  // as it's internal and technically not nullable, we don't care about null pointer state
+  // and don't need destructive move
+  TEST_CONSTEXPR_CXX14 thread_unsafe_shared_ptr(const thread_unsafe_shared_ptr& other) TEST_NOEXCEPT
----------------
kitsnet wrote:

This one is also better to discuss in https://github.com/llvm/llvm-project/pull/195932 .

The goal for fancy_pointer_allocator was to introduce an allocator for a fancy pointer class that:
1. Has all its special methods non-trivial;
2. Is suitable to detecting at least single errors of non-calling nontrivial methods in our handling of the union inside std::basic_string;
3. Is C++20+ consteval friendly - for static_assert tests.

The (3) is a huge limitation in the ways how we can track the calls of our special methods. Fortunately, we already had a class in our testing framework that could be used as a shared state for such tracing (`thread_unsafe_shared_ptr`). Unfortunately, it had some inconsistencies that should have been fixed.

https://github.com/llvm/llvm-project/pull/196187