[libc++] Fix ADL for `make_error_{code,condition}`

[ldionne]

Summary

Implement LWG 3629, by making lookup for make_error_code and
make_error_condition only consider names found by ADL. This is achieved
by adding a block scope using-declaration for a function that will be
found by unqualified lookup, preventing unqualified lookup from
continuing to enclosing scopes (the class scope, then enclosing
namespaces). The function named by the using declaration is not
viable, so overload resolution must select a candidate found by ADL.

This fixes https://github.com/llvm/llvm-project/issues/57614

[ldionne]

Thanks a lot for the patch Jonathan. I'll commandeer to fix up a few remaining things, I assume this is okay with you.

[ldionne]

Address C++03 errors, add to LWG issues list and a few other nits. Thanks Jonathan!

[jwakely]

In D134943#3826926, @ldionne wrote:

I assume this is okay with you.

Absolutely! I can't commit it myself anyway, so you might as well fix what needs fixing and commit. Thanks.

[jwakely]

I've just noticed the summary says "The function names by the using declaration" which should be _named_ not names.

[ldionne]

Update commit message, remove = delete since they are not technically required.

[ldionne]

Please clang-tidy. Always use = delete because Clang supports it even in C++03.

libcxx/docs/Status/Cxx2bIssues.csv

 "`3711 <https://wg21.link/LWG3711>`__","Missing preconditions for slide_view constructor","July 2022","","","|ranges|"
 "`3712 <https://wg21.link/LWG3712>`__","``chunk_view`` and ``slide_view`` should not be ``default_initializable``","July 2022","","","|ranges|"
 "`3713 <https://wg21.link/LWG3713>`__","Sorted with respect to comparator (only)","July 2022","",""
 "`3715 <https://wg21.link/LWG3715>`__","``view_interface::empty`` is overconstrained","July 2022","",""
 "`3719 <https://wg21.link/LWG3719>`__","Directory iterators should be usable with default sentinel","July 2022","",""
 "`3721 <https://wg21.link/LWG3721>`__","Allow an ``arg-id`` with a value of zero for ``width`` in ``std-format-spec``","July 2022","|Complete|","16.0","|format|"
 "`3724 <https://wg21.link/LWG3724>`__","``decay-copy`` should be constrained","July 2022","|Complete|","14.0"
 "","","","",""
-"`3645 <https://wg21.link/LWG3645>`__","``resize_and_overwrite`` is overspecified to call its callback with lvalues","Not voted in","|Complete|","14.0",""
+"`3629 <https://wg21.link/LWG3629>`__","``make_error_code`` and ``make_error_condition`` are customization points","Not voted in","|Complete|","16.0",""
 "`3631 <https://wg21.link/LWG3631>`__","``basic_format_arg(T&&)`` should use ``remove_cvref_t<T>`` throughout","Not voted in","|Complete|","15.0",""
+"`3645 <https://wg21.link/LWG3645>`__","``resize_and_overwrite`` is overspecified to call its callback with lvalues","Not voted in","|Complete|","14.0",""
 "","","","",""

libcxx/include/system_error

 {
 public:
     string message(int __ev) const override;
 };
 
 _LIBCPP_FUNC_VIS const error_category& generic_category() _NOEXCEPT;
 _LIBCPP_FUNC_VIS const error_category& system_category() _NOEXCEPT;
 
+namespace __adl_only {
+    // Those cause ADL to trigger but they are not viable candidates,
+    // so they are never actually selected.
+    void make_error_condition() = delete;
+    void make_error_code() = delete;
+} // namespace __adl_only
+
 class _LIBCPP_TYPE_VIS error_condition
 {
     int __val_;
     const error_category* __cat_;
 public:
     _LIBCPP_INLINE_VISIBILITY
     error_condition() _NOEXCEPT : __val_(0), __cat_(&generic_category()) {}
 
     _LIBCPP_INLINE_VISIBILITY
     error_condition(int __val, const error_category& __cat) _NOEXCEPT
         : __val_(__val), __cat_(&__cat) {}
 
     template <class _Ep>
         _LIBCPP_INLINE_VISIBILITY
         error_condition(_Ep __e,
               typename enable_if<is_error_condition_enum<_Ep>::value>::type* = nullptr
                                                                      ) _NOEXCEPT
-            {*this = make_error_condition(__e);}
+            {
+                using __adl_only::make_error_condition;
+                *this = make_error_condition(__e);
+            }
 
     _LIBCPP_INLINE_VISIBILITY
     void assign(int __val, const error_category& __cat) _NOEXCEPT
     {
         __val_ = __val;
         __cat_ = &__cat;
     }
 
     template <class _Ep>
         _LIBCPP_INLINE_VISIBILITY
         typename enable_if
         <
             is_error_condition_enum<_Ep>::value,
             error_condition&
         >::type
         operator=(_Ep __e) _NOEXCEPT
-            {*this = make_error_condition(__e); return *this;}
+            {
+                using __adl_only::make_error_condition;
+                *this = make_error_condition(__e);
+                return *this;
+            }
 
     _LIBCPP_INLINE_VISIBILITY
     void clear() _NOEXCEPT
     {
         __val_ = 0;
         __cat_ = &generic_category();
     }
 
public:
     error_code(int __val, const error_category& __cat) _NOEXCEPT
         : __val_(__val), __cat_(&__cat) {}
 
     template <class _Ep>
         _LIBCPP_INLINE_VISIBILITY
         error_code(_Ep __e,
                    typename enable_if<is_error_code_enum<_Ep>::value>::type* = nullptr
                                                                      ) _NOEXCEPT
-            {*this = make_error_code(__e);}
+            {
+                using __adl_only::make_error_code;
+                *this = make_error_code(__e);
+            }
 
     _LIBCPP_INLINE_VISIBILITY
     void assign(int __val, const error_category& __cat) _NOEXCEPT
     {
         __val_ = __val;
         __cat_ = &__cat;
     }
 
     template <class _Ep>
         _LIBCPP_INLINE_VISIBILITY
         typename enable_if
         <
             is_error_code_enum<_Ep>::value,
             error_code&
         >::type
         operator=(_Ep __e) _NOEXCEPT
-            {*this = make_error_code(__e); return *this;}
+            {
+                using __adl_only::make_error_code;
+                *this = make_error_code(__e);
+                return *this;
+            }
 
     _LIBCPP_INLINE_VISIBILITY
     void clear() _NOEXCEPT
     {
         __val_ = 0;
         __cat_ = &system_category();
     }
 

libcxx/test/std/diagnostics/syserr/syserr.errcode/syserr.errcode.constructors/lwg3629.pass.cpp

+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+// <system_error>
+
+// class error_code
+
+// template <ErrorCodeEnum E> error_code(E e);
+
+// Regression test for https://github.com/llvm/llvm-project/issues/57614
+
+int make_error_code; // It's important that this comes before <system_error>
+
+#include <system_error>
+#include <cassert>
+#include <type_traits>
+
+namespace user {
+  enum Err {};
+
+  std::error_code make_error_code(Err) { return std::error_code(42, std::generic_category()); }
+}
+
+namespace std {
+  template <>
+  struct is_error_code_enum<user::Err> : true_type {};
+}
+
+int main(int, char**) {
+  std::error_code e((user::Err()));
+  assert(e.value() == 42);
+  assert(e.category() == std::generic_category());
+
+  return 0;
+}

libcxx/test/std/diagnostics/syserr/syserr.errcode/syserr.errcode.modifiers/lwg3629.pass.cpp

+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+// <system_error>
+
+// class error_code
+
+// template <ErrorCodeEnum E> error_code& operator=(E e);
+
+// Regression test for https://github.com/llvm/llvm-project/issues/57614
+
+int make_error_code; // It's important that this comes before <system_error>
+
+#include <system_error>
+#include <cassert>
+#include <type_traits>
+
+namespace user {
+  enum Err {};
+
+  std::error_code make_error_code(Err) { return std::error_code(42, std::generic_category()); }
+}
+
+namespace std {
+  template <>
+  struct is_error_code_enum<user::Err> : true_type {};
+}
+
+int main(int, char**) {
+  std::error_code e;
+  e = user::Err();
+  assert(e.value() == 42);
+  assert(e.category() == std::generic_category());
+
+  return 0;
+}

libcxx/test/std/diagnostics/syserr/syserr.errcondition/syserr.errcondition.constructors/lwg3629.pass.cpp

+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+// <system_error>
+
+// class error_condition
+
+// template <ErrorCodeEnum E> error_condition(E e);
+
+// Regression test for https://github.com/llvm/llvm-project/issues/57614
+
+int make_error_condition; // It's important that this comes before <system_error>
+
+#include <system_error>
+#include <cassert>
+#include <type_traits>
+
+namespace user {
+  enum Err {};
+
+  std::error_condition make_error_condition(Err) { return std::error_condition(42, std::generic_category()); }
+}
+
+namespace std {
+  template <>
+  struct is_error_condition_enum<user::Err> : true_type {};
+}
+
+int main(int, char**) {
+  std::error_condition e((user::Err()));
+  assert(e.value() == 42);
+  assert(e.category() == std::generic_category());
+
+  return 0;
+}

libcxx/test/std/diagnostics/syserr/syserr.errcondition/syserr.errcondition.modifiers/lwg3629.pass.cpp

+//===----------------------------------------------------------------------===//
+//
+// 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
+//
+//===----------------------------------------------------------------------===//
+
+// <system_error>
+
+// class error_condition
+
+// template <ErrorCodeEnum E> error_condition& operator=(E e);
+
+// Regression test for https://github.com/llvm/llvm-project/issues/57614
+
+int make_error_condition; // It's important that this comes before <system_error>
+
+#include <system_error>
+#include <cassert>
+#include <type_traits>
+
+#include "test_macros.h"
+
+namespace user {
+  enum Err {};
+
+  std::error_condition make_error_condition(Err) { return std::error_condition(42, std::generic_category()); }
+}
+
+namespace std {
+  template <>
+  struct is_error_condition_enum<user::Err> : true_type {};
+}
+
+int main(int, char**) {
+  std::error_condition e;
+  e = user::Err();
+  assert(e.value() == 42);
+  assert(e.category() == std::generic_category());
+  return 0;
+}