[Libcxx] Add <source_location> header.

This requires the __builtin_source_location() builtin, as implemented
by GCC and Clang.

Fixes #56363

Differential Revision: https://reviews.llvm.org/D120634

Author: jyknight

libcxx/docs/FeatureTestMacroTable.rst

@@ -274,7 +274,7 @@ Status
     ------------------------------------------------- -----------------
     ``__cpp_lib_smart_ptr_for_overwrite``             *unimplemented*
     ------------------------------------------------- -----------------
-    ``__cpp_lib_source_location``                     *unimplemented*
+    ``__cpp_lib_source_location``                     ``201907L``
     ------------------------------------------------- -----------------
     ``__cpp_lib_span``                                ``202002L``
     ------------------------------------------------- -----------------

libcxx/docs/ReleaseNotes.rst

@@ -51,6 +51,7 @@ Implemented Papers
 - P0339R6 - ``polymorphic_allocator<>`` as a vocabulary type
 - P1169R4 - ``static operator()``
 - P0415R1 - ``constexpr`` for ``std::complex``
+- P1208R6 - ``std::source_location``
 
 Improvements and New Features
 -----------------------------

libcxx/docs/Status/Cxx20Issues.csv

@@ -295,7 +295,7 @@
 "`3390 <https://wg21.link/LWG3390>`__","``make_move_iterator()``\  cannot be used to construct a ``move_iterator``\  for a move-only iterator","Prague","|Complete|","14.0","|ranges|"
 "`3393 <https://wg21.link/LWG3393>`__","Missing/incorrect feature test macro for coroutines","Prague","|Complete|","14.0"
 "`3395 <https://wg21.link/LWG3395>`__","Definition for three-way comparison needs to be updated (US 152)","Prague","","","|spaceship|"
-"`3396 <https://wg21.link/LWG3396>`__","Clarify point of reference for ``source_location::current()``\  (DE 169)","Prague","",""
+"`3396 <https://wg21.link/LWG3396>`__","Clarify point of reference for ``source_location::current()``\  (DE 169)","Prague","|Nothing To Do|","16.0"
 "`3397 <https://wg21.link/LWG3397>`__","``ranges::basic_istream_view::iterator``\  should not provide ``iterator_category``\ ","Prague","|Complete|","16.0","|ranges|"
 "`3398 <https://wg21.link/LWG3398>`__","``tuple_element_t``\  is also wrong for ``const subrange``\ ","Prague","|Complete|","14.0","|ranges|"
 "`3446 <https://wg21.link/LWG3446>`__","``indirectly_readable_traits``\  ambiguity for types with both ``value_type``\  and ``element_type``\ ","November virtual meeting","|Complete|","13.0","|ranges|"

libcxx/docs/Status/Cxx20Papers.csv

@@ -112,7 +112,7 @@
 "`P1065R2 <https://wg21.link/P1065R2>`__","LWG","Constexpr INVOKE","Cologne","|Complete|","12.0"
 "`P1135R6 <https://wg21.link/P1135R6>`__","LWG","The C++20 Synchronization Library","Cologne","|Complete|","11.0"
 "`P1207R4 <https://wg21.link/P1207R4>`__","LWG","Movability of Single-pass Iterators","Cologne","|Complete|","15.0","|ranges|"
-"`P1208R6 <https://wg21.link/P1208R6>`__","LWG","Adopt source_location for C++20","Cologne","",""
+"`P1208R6 <https://wg21.link/P1208R6>`__","LWG","Adopt source_location for C++20","Cologne","|Complete|","16.0"
 "`P1355R2 <https://wg21.link/P1355R2>`__","LWG","Exposing a narrow contract for ceil2","Cologne","|Complete|","9.0"
 "`P1361R2 <https://wg21.link/P1361R2>`__","LWG","Integration of chrono with text formatting","Cologne","|In Progress|",""
 "`P1423R3 <https://wg21.link/P1423R3>`__","LWG","char8_t backward compatibility remediation","Cologne","|Complete|","15.0"

libcxx/include/CMakeLists.txt

@@ -824,6 +824,7 @@ set(files
   set
   setjmp.h
   shared_mutex
+  source_location
   span
   sstream
   stack

libcxx/include/module.modulemap.in

@@ -1291,6 +1291,10 @@ module std [system] {
     header "shared_mutex"
     export version
   }
+  module source_location {
+    header "source_location"
+    export *
+  }
   module span {
     header "span"
     export ranges.__ranges.enable_borrowed_range

libcxx/include/source_location

@@ -0,0 +1,85 @@
+// -*- C++ -*-
+//===----------------------------------------------------------------------===//
+//
+// 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_SOURCE_LOCATION
+#define _LIBCPP_SOURCE_LOCATION
+
+/* source_location synopsis
+
+namespace std {
+  struct source_location {
+    static consteval source_location current() noexcept;
+    constexpr source_location() noexcept;
+
+    constexpr uint_least32_t line() const noexcept;
+    constexpr uint_least32_t column() const noexcept;
+    constexpr const char* file_name() const noexcept;
+    constexpr const char* function_name() const noexcept;
+  };
+}
+*/
+
+#include <__config>
+#include <cstdint>
+#include <version>
+
+#if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
+#  pragma GCC system_header
+#endif
+
+_LIBCPP_BEGIN_NAMESPACE_STD
+
+#if _LIBCPP_STD_VER >= 20 && __has_builtin(__builtin_source_location)
+
+class source_location {
+  // The names source_location::__impl, _M_file_name, _M_function_name, _M_line, and _M_column
+  // are hard-coded in the compiler and must not be changed here.
+  struct __impl {
+    const char* _M_file_name;
+    const char* _M_function_name;
+    unsigned _M_line;
+    unsigned _M_column;
+  };
+  const __impl* __ptr_ = nullptr;
+  // GCC returns the type 'const void*' from the builtin, while clang returns
+  // `const __impl*`. Per C++ [expr.const], casts from void* are not permitted
+  // in constant evaluation, so we don't want to use `void*` as the argument
+  // type unless the builtin returned that, anyhow, and the invalid cast is
+  // unavoidable.
+  using __bsl_ty = decltype(__builtin_source_location());
+
+public:
+  // The defaulted __ptr argument is necessary so that the builtin is evaluated
+  // in the context of the caller. An explicit value should never be provided.
+  static consteval source_location current(__bsl_ty __ptr = __builtin_source_location()) noexcept {
+    source_location __sl;
+    __sl.__ptr_ = static_cast<const __impl*>(__ptr);
+    return __sl;
+  }
+  _LIBCPP_HIDE_FROM_ABI constexpr source_location() noexcept = default;
+
+  _LIBCPP_HIDE_FROM_ABI constexpr uint_least32_t line() const noexcept {
+    return __ptr_ != nullptr ? __ptr_->_M_line : 0;
+  }
+  _LIBCPP_HIDE_FROM_ABI constexpr uint_least32_t column() const noexcept {
+    return __ptr_ != nullptr ? __ptr_->_M_column : 0;
+  }
+  _LIBCPP_HIDE_FROM_ABI constexpr const char* file_name() const noexcept {
+    return __ptr_ != nullptr ? __ptr_->_M_file_name : "";
+  }
+  _LIBCPP_HIDE_FROM_ABI constexpr const char* function_name() const noexcept {
+    return __ptr_ != nullptr ? __ptr_->_M_function_name : "";
+  }
+};
+
+#endif // _LIBCPP_STD_VER >= 20 && __has_builtin(__builtin_source_location)
+
+_LIBCPP_END_NAMESPACE_STD
+
+#endif // _LIBCPP_SOURCE_LOCATION

libcxx/include/version

@@ -365,7 +365,9 @@ __cpp_lib_void_t                                        201411L <type_traits>
 # define __cpp_lib_shared_ptr_arrays                    201707L
 # define __cpp_lib_shift                                201806L
 // # define __cpp_lib_smart_ptr_for_overwrite              202002L
-// # define __cpp_lib_source_location                      201907L
+# if __has_builtin(__builtin_source_location)
+#   define __cpp_lib_source_location                    201907L
+# endif
 # define __cpp_lib_span                                 202002L
 # define __cpp_lib_ssize                                201902L
 # define __cpp_lib_starts_ends_with                     201711L