compat: do not use std::source_location if it is broken

in a recent clang change, __builtin_source_location was added.
see https://reviews.llvm.org/rGd61487490022 . but a bug in clang
frontend pratically prevents us from using it. see
llvm/llvm-project#48230. so before this
issue is fixed, we have to prevent clang from using the builtin
source location implementation.

in this change, a new library is added for introducing the macro
of "SEASTAR_BROKEN_SOURCE_LOCATION", if it is defined we'd have to
use the homebrew implementation of source_location even the header
file of <source_location> or <experimental/source_location> can be
found by the C++ compiler.

please note, -std=c++20 is not added to CMAKE_REQUIRED_FLAGS when
performing the test, because we want to ensure that we are using
the same CXX_FLAGS as the ones when compiling std-compat.hh.

Signed-off-by: Kefu Chai <tchaikov@gmail.com>

CMakeLists.txt

@@ -737,6 +737,7 @@ target_link_libraries (seastar
     cryptopp::cryptopp
     fmt::fmt
     lz4::lz4
+    SourceLocation::source_location
   PRIVATE
     ${CMAKE_DL_LIBS}
     GnuTLS::gnutls
@@ -1238,6 +1239,7 @@ if (Seastar_INSTALL)
       ${CMAKE_CURRENT_SOURCE_DIR}/cmake/FindGnuTLS.cmake
       ${CMAKE_CURRENT_SOURCE_DIR}/cmake/FindLinuxMembarrier.cmake
       ${CMAKE_CURRENT_SOURCE_DIR}/cmake/FindSanitizers.cmake
+      ${CMAKE_CURRENT_SOURCE_DIR}/cmake/FindSourceLocation.cmake
       ${CMAKE_CURRENT_SOURCE_DIR}/cmake/FindStdAtomic.cmake
       ${CMAKE_CURRENT_SOURCE_DIR}/cmake/Findc-ares.cmake
       ${CMAKE_CURRENT_SOURCE_DIR}/cmake/Findcryptopp.cmake

cmake/FindSourceLocation.cmake

@@ -0,0 +1,40 @@
+#
+# This file is open source software, licensed to you under the terms
+# of the Apache License, Version 2.0 (the "License").  See the NOTICE file
+# distributed with this work for additional information regarding copyright
+# ownership.  You may not use this file except in compliance with the License.
+#
+# You may obtain a copy of the License at
+#
+#   http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing,
+# software distributed under the License is distributed on an
+# "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+# KIND, either express or implied.  See the License for the
+# specific language governing permissions and limitations
+# under the License.
+#
+
+#
+# Copyright (C) 2022 Kefu Chai ( tchaikov@gmail.com )
+#
+
+include (CheckCXXSourceCompiles)
+include(CMakePushCheckState)
+
+file (READ ${CMAKE_CURRENT_LIST_DIR}/code_tests/Source_location_test.cc _source_location_test_code)
+cmake_push_check_state ()
+set(CMAKE_CXX_STANDARD ${Seastar_CXX_STANDARD})
+# set(CMAKE_REQUIRED_FLAGS "-std=${Seastar_CXX_STANDARD}")
+check_cxx_source_compiles ("${_source_location_test_code}" CxxSourceLocation_SUPPORTED)
+cmake_pop_check_state ()
+
+if (NOT (TARGET SourceLocation::source_location))
+  add_library (SourceLocation::source_location INTERFACE IMPORTED)
+  if  (NOT CxxSourceLocation_SUPPORTED)
+    set_target_properties (SourceLocation::source_location
+      PROPERTIES
+        INTERFACE_COMPILE_DEFINITIONS SEASTAR_BROKEN_SOURCE_LOCATION)
+  endif ()
+endif ()

cmake/SeastarDependencies.cmake

@@ -60,6 +60,7 @@ macro (seastar_find_dependencies)
     GnuTLS
     LinuxMembarrier
     Sanitizers
+    SourceLocation
     StdAtomic
     hwloc
     lksctp-tools # No version information published.

cmake/code_tests/Source_location_test.cc

@@ -0,0 +1,26 @@
+#if __has_include(<source_location>)
+#include <source_location>
+#endif
+
+#ifdef __cpp_lib_source_location
+using source_location = std::source_location;
+#elif __has_include(<experimental/source_location>)
+#include <experimental/source_location>
+using source_location = std::experimental::source_location;
+#endif
+
+#if defined(__cpp_lib_source_location) || defined(__cpp_lib_experimental_source_location)
+struct format_info {
+    format_info(source_location loc = source_location::current()) noexcept
+        : loc(loc)
+    { }
+    source_location loc;
+};
+#else
+struct format_info { };
+#endif
+
+int main()
+{
+    format_info fi;
+}

include/seastar/util/std-compat.hh

@@ -57,11 +57,11 @@ namespace std::pmr {
 #include <source_location>
 #endif
 
-#ifdef __cpp_lib_source_location
+#if defined(__cpp_lib_source_location) && !defined(SEASTAR_BROKEN_SOURCE_LOCATION)
 namespace seastar::compat {
 using source_location = std::source_location;
 }
-#elif __has_include(<experimental/source_location>)
+#elif __has_include(<experimental/source_location>) && !defined(SEASTAR_BROKEN_SOURCE_LOCATION)
 #include <experimental/source_location>
 namespace seastar::compat {
 using source_location = std::experimental::source_location;