[libc++] Remove usage of `_LIBCPP_DEBUG` in `__comp_ref_type` and replace with `_LIBCPP_DEBUG_LEVEL`

[rupprecht]

Summary

In libc++, checking specific _LIBCPP_DEBUG_LEVEL levels is used everywhere except in comp_ref_type.h. _LIBCPP_DEBUG is meant as a user-facing option, and internally libc++ should be checking the value of _LIBCPP_DEBUG_LEVEL.

The definition of std::__debug_less doesn't need to be hidden behind the macro, we can unconditionally expose it. It will be unused by __comp_ref_type unless debug mode is enabled.

This was suggested in D118940.

[philnik]

LGTM if CI is green. I'd still like to see _LIBCPP_HIDE_FROM_ABI, but I'm not making you replace it. We replace it incrementally because it would be a huge change.

[• Quuxplusone]

This looks fine to me, but I would feel better if @ldionne also looked at it.

[ldionne]

This looks correct to me, but thanks for waiting. The debug mode is sometimes tricky, but in this case this really looks like an oversight. Basically, _LIBCPP_DEBUG is the user-facing option, and the library should use _LIBCPP_DEBUG_LEVEL internally.

However, the commit summary says "Remove _LIBCPP_DEBUG and replace with _LIBCPP_DEBUG_LEVEL", which is misleading. I thought you were removing _LIBCPP_DEBUG entirely at first. I think this would be better: "Remove usage of _LIBCPP_DEBUG in __comp_ref_type" or something along those lines.

[rupprecht]

In D118950#3297998, @ldionne wrote:

This looks correct to me, but thanks for waiting. The debug mode is sometimes tricky, but in this case this really looks like an oversight. Basically, _LIBCPP_DEBUG is the user-facing option, and the library should use _LIBCPP_DEBUG_LEVEL internally.

However, the commit summary says "Remove _LIBCPP_DEBUG and replace with _LIBCPP_DEBUG_LEVEL", which is misleading. I thought you were removing _LIBCPP_DEBUG entirely at first. I think this would be better: "Remove usage of _LIBCPP_DEBUG in __comp_ref_type" or something along those lines.

Done, and added your elaboration on the user-facing vs internal difference, thanks for that clarification.

libcxx/include/__algorithm/comp_ref_type.h

 //===----------------------------------------------------------------------===//
 //
 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
 // See https://llvm.org/LICENSE.txt for license information.
 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
 //
 //===----------------------------------------------------------------------===//
 
 #ifndef _LIBCPP___ALGORITHM_COMP_REF_TYPE_H
 #define _LIBCPP___ALGORITHM_COMP_REF_TYPE_H
 
 #include <__config>
-
-#ifdef _LIBCPP_DEBUG
-#  include <__debug>
-#  include <__utility/declval.h>
-#endif
+#include <__debug>
+#include <__utility/declval.h>
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #  pragma GCC system_header
 #endif
 
 _LIBCPP_BEGIN_NAMESPACE_STD
 
-#ifdef _LIBCPP_DEBUG
-
 template <class _Compare>
 struct __debug_less
 {
     _Compare &__comp_;
     _LIBCPP_CONSTEXPR_AFTER_CXX11
     __debug_less(_Compare& __c) : __comp_(__c) {}
 
     template <class _Tp, class _Up>
struct __debug_less
     template <class _LHS, class _RHS>
     _LIBCPP_CONSTEXPR_AFTER_CXX11
     inline _LIBCPP_INLINE_VISIBILITY
     decltype((void)declval<_Compare&>()(
         declval<_LHS &>(), declval<_RHS &>()))
     __do_compare_assert(int, _LHS & __l, _RHS & __r) {
         _LIBCPP_ASSERT(!__comp_(__l, __r),
             "Comparator does not induce a strict weak ordering");
+        (void)__l;
+        (void)__r;
     }
 
     template <class _LHS, class _RHS>
     _LIBCPP_CONSTEXPR_AFTER_CXX11
     inline _LIBCPP_INLINE_VISIBILITY
     void __do_compare_assert(long, _LHS &, _RHS &) {}
 };
 
-#endif // _LIBCPP_DEBUG
-
 template <class _Comp>
 struct __comp_ref_type {
   // Pass the comparator by lvalue reference. Or in debug mode, using a
   // debugging wrapper that stores a reference.
-#ifndef _LIBCPP_DEBUG
+#if _LIBCPP_DEBUG_LEVEL == 0
   typedef _Comp& type;
 #else
   typedef __debug_less<_Comp> type;
 #endif
 };
 
 _LIBCPP_END_NAMESPACE_STD
 
 #endif // _LIBCPP___ALGORITHM_COMP_REF_TYPE_H