[lldb][test] Add a layout simulator test for std::unique_ptr (#98330)

This is motivated by the upcoming refactor of libc++'s
`__compressed_pair` in #76756

As this will require changes to numerous LLDB libc++ data-formatters
(see early draft #96538), it
would be nice to have a test-suite that will actually exercise both the
old and new layout. We have a matrix bot that tests old versions of
Clang (but currently those only date back to Clang-15). Having them in
the test-suite will give us quicker signal on what broke.

We have an existing test that exercises various layouts of `std::string`
over time in `TestDataFormatterLibcxxStringSimulator.py`, but that's the
only STL type we have it for. This patch proposes a new
`libcxx-simulators` directory which will take the same approach for all
the STL types that we can feasibly support in this way (as @labath
points out, for some types this might just not be possible due to their
implementation complexity). Nonetheless, it'd be great to have a record
of how the layout of libc++ types changed over time.

Some related discussion:
*
#97568 (comment)

lldb/packages/Python/lldbsuite/test/make/libcxx-simulators-common/compressed_pair.h

@@ -0,0 +1,58 @@
+#ifndef STD_LLDB_COMPRESSED_PAIR_H
+#define STD_LLDB_COMPRESSED_PAIR_H
+
+#include <type_traits>
+#include <utility> // for std::forward
+
+namespace std {
+namespace __lldb {
+
+// Post-c88580c layout
+struct __value_init_tag {};
+struct __default_init_tag {};
+
+template <class _Tp, int _Idx,
+          bool _CanBeEmptyBase =
+              std::is_empty<_Tp>::value && !std::is_final<_Tp>::value>
+struct __compressed_pair_elem {
+  explicit __compressed_pair_elem(__default_init_tag) {}
+  explicit __compressed_pair_elem(__value_init_tag) : __value_() {}
+
+  explicit __compressed_pair_elem(_Tp __t) : __value_(__t) {}
+
+  _Tp &__get() { return __value_; }
+
+private:
+  _Tp __value_;
+};
+
+template <class _Tp, int _Idx>
+struct __compressed_pair_elem<_Tp, _Idx, true> : private _Tp {
+  explicit __compressed_pair_elem(_Tp __t) : _Tp(__t) {}
+  explicit __compressed_pair_elem(__default_init_tag) {}
+  explicit __compressed_pair_elem(__value_init_tag) : _Tp() {}
+
+  _Tp &__get() { return *this; }
+};
+
+template <class _T1, class _T2>
+class __compressed_pair : private __compressed_pair_elem<_T1, 0>,
+                          private __compressed_pair_elem<_T2, 1> {
+public:
+  using _Base1 = __compressed_pair_elem<_T1, 0>;
+  using _Base2 = __compressed_pair_elem<_T2, 1>;
+
+  explicit __compressed_pair(_T1 __t1, _T2 __t2) : _Base1(__t1), _Base2(__t2) {}
+  explicit __compressed_pair()
+      : _Base1(__value_init_tag()), _Base2(__value_init_tag()) {}
+
+  template <class _U1, class _U2>
+  explicit __compressed_pair(_U1 &&__t1, _U2 &&__t2)
+      : _Base1(std::forward<_U1>(__t1)), _Base2(std::forward<_U2>(__t2)) {}
+
+  _T1 &first() { return static_cast<_Base1 &>(*this).__get(); }
+};
+} // namespace __lldb
+} // namespace std
+
+#endif // _H

lldb/test/API/functionalities/data-formatter/data-formatter-stl/libcxx-simulators/unique_ptr/Makefile

@@ -0,0 +1,3 @@
+CXX_SOURCES := main.cpp
+override CXXFLAGS_EXTRAS += -std=c++14
+include Makefile.rules

lldb/test/API/functionalities/data-formatter/data-formatter-stl/libcxx-simulators/unique_ptr/TestDataFormatterLibcxxUniquePtrSimulator.py

@@ -0,0 +1,24 @@
+"""
+Test we can understand various layouts of the libc++'s std::unique_ptr
+"""
+
+
+import lldb
+from lldbsuite.test.decorators import *
+from lldbsuite.test.lldbtest import *
+from lldbsuite.test import lldbutil
+
+
+class LibcxxUniquePtrDataFormatterSimulatorTestCase(TestBase):
+    NO_DEBUG_INFO_TESTCASE = True
+
+    def test(self):
+        self.build()
+        lldbutil.run_to_source_breakpoint(
+            self, "Break here", lldb.SBFileSpec("main.cpp")
+        )
+        self.expect("frame variable var_up", substrs=["pointer ="])
+        self.expect("frame variable var_up", substrs=["deleter ="], matching=False)
+        self.expect(
+            "frame variable var_with_deleter_up", substrs=["pointer =", "deleter ="]
+        )

lldb/test/API/functionalities/data-formatter/data-formatter-stl/libcxx-simulators/unique_ptr/main.cpp

@@ -0,0 +1,37 @@
+#include <libcxx-simulators-common/compressed_pair.h>
+
+namespace std {
+namespace __lldb {
+template <class _Tp> struct default_delete {
+  default_delete() noexcept = default;
+
+  void operator()(_Tp *__ptr) const noexcept { delete __ptr; }
+};
+
+template <class _Tp, class _Dp = default_delete<_Tp>> class unique_ptr {
+public:
+  typedef _Tp element_type;
+  typedef _Dp deleter_type;
+  typedef _Tp *pointer;
+
+  std::__lldb::__compressed_pair<pointer, deleter_type> __ptr_;
+  explicit unique_ptr(pointer __p) noexcept
+      : __ptr_(__p, std::__lldb::__value_init_tag()) {}
+};
+} // namespace __lldb
+} // namespace std
+
+struct StatefulDeleter {
+  StatefulDeleter() noexcept = default;
+
+  void operator()(int *__ptr) const noexcept { delete __ptr; }
+
+  int m_state = 50;
+};
+
+int main() {
+  std::__lldb::unique_ptr<int> var_up(new int(5));
+  std::__lldb::unique_ptr<int, StatefulDeleter> var_with_deleter_up(new int(5));
+  __builtin_printf("Break here\n");
+  return 0;
+}

lldb/test/API/functionalities/data-formatter/data-formatter-stl/libcxx/string/simulator/main.cpp

@@ -1,3 +1,5 @@
+#include <libcxx-simulators-common/compressed_pair.h>
+
 #include <climits>
 #include <memory>
 #include <type_traits>
@@ -32,37 +34,6 @@
 namespace std {
 namespace __lldb {
 
-template <class _Tp, int _Idx,
-          bool _CanBeEmptyBase =
-              std::is_empty<_Tp>::value && !std::is_final<_Tp>::value>
-struct __compressed_pair_elem {
-  explicit __compressed_pair_elem(_Tp __t) : __value_(__t) {}
-
-  _Tp &__get() { return __value_; }
-
-private:
-  _Tp __value_;
-};
-
-template <class _Tp, int _Idx>
-struct __compressed_pair_elem<_Tp, _Idx, true> : private _Tp {
-  explicit __compressed_pair_elem(_Tp __t) : _Tp(__t) {}
-
-  _Tp &__get() { return *this; }
-};
-
-template <class _T1, class _T2>
-class __compressed_pair : private __compressed_pair_elem<_T1, 0>,
-                          private __compressed_pair_elem<_T2, 1> {
-public:
-  using _Base1 = __compressed_pair_elem<_T1, 0>;
-  using _Base2 = __compressed_pair_elem<_T2, 1>;
-
-  explicit __compressed_pair(_T1 __t1, _T2 __t2) : _Base1(__t1), _Base2(__t2) {}
-
-  _T1 &first() { return static_cast<_Base1 &>(*this).__get(); }
-};
-
 #if defined(ALTERNATE_LAYOUT) && defined(SUBCLASS_PADDING)
 template <class _CharT, size_t = sizeof(_CharT)> struct __padding {
   unsigned char __xx[sizeof(_CharT) - 1];
@@ -212,7 +183,7 @@ template <class _CharT, class _Traits, class _Allocator> class basic_string {
     };
   };
 
-  __compressed_pair<__rep, allocator_type> __r_;
+  std::__lldb::__compressed_pair<__rep, allocator_type> __r_;
 
 public:
   template <size_t __N>