Fix std::variant, std::filesystem::path tests on GCC-8, Clang-7,8. #2951

phprus · 2022-06-28T17:35:58Z

libstdc++ from GCC-8 support std::variant.
libstdc++ from GCC-8 has no <version> file.
libstdc++ from GCC-8 defines the macro __cpp_lib_variant in <variant>.

fmt/test/gtest/gtest/gtest.h

Lines 2621 to 2627 in 6a775e9

    
           #ifdef __has_include 
        
           #if __has_include(<variant>) && __cplusplus >= 201703L 
        
           // Otherwise for C++17 and higher use std::variant for UniversalPrinter<> 
        
           // specializations. 
        
           #define GTEST_INTERNAL_HAS_VARIANT 1 
        
           #include <variant> 
        
           namespace testing {

Because gtest.h include <variant>, then the macro __cpp_lib_variant is defined in the test, but is not defined in "fmt/std.h".

vitaut

Thanks for the PR. Unfortunately it only masks the issue so I suggest including <variant> in fmt/std.h when the header exists instead. This can be checked with FMT_HAS_INCLUDE.

phprus · 2022-06-30T16:33:17Z

@vitaut, Done.
I have added two new CI configurations to detect such errors.

vitaut · 2022-07-01T14:02:25Z

include/fmt/std.h

@@ -17,10 +17,16 @@
 #if FMT_HAS_INCLUDE(<version>)
 #  include <version>
 #endif
+#if FMT_CPLUSPLUS >= 201703L


What is this check for? Shouldn't FMT_HAS_INCLUDE and feature test macro checks be enough?

Without FMT_CPLUSPLUS check:
libstdc++: ok (Checking the version of C++ standard is present)
libcxx: ok (Checking the version of C++ standard is absent)
MSVC message:

#if !_HAS_CXX17 #pragma message("The contents of <filesystem> are available only with C++17 or later.") #else // ^^^ !_HAS_CXX17 / _HAS_CXX17 vvv

https://github.com/microsoft/STL/blob/c34f24920e463a71791c2ee3d2bed14926518965/stl/inc/filesystem#L12-L14
https://github.com/microsoft/STL/blob/c34f24920e463a71791c2ee3d2bed14926518965/stl/inc/variant#L12-L14
https://godbolt.org/z/1MM9Kee8n

For this reason, a check is required.

Could you add a short comment clarifying that this check is for MSVC?

@vitaut Done

vitaut · 2022-07-01T14:06:21Z

test/CMakeLists.txt

+try_compile(compile_result_unused
+            ${CMAKE_CURRENT_BINARY_DIR}
+            SOURCES ${CMAKE_CURRENT_LIST_DIR}/detect-stdfs.cc
+            CMAKE_FLAGS CMAKE_OSX_ARCHITECTURES=${CMAKE_OSX_ARCHITECTURES}
+            OUTPUT_VARIABLE RAWOUTPUT)
+string(REGEX REPLACE ".*libfound \"([^\"]*)\".*" "\\1" STDLIBFS "${RAWOUTPUT}")
+if (STDLIBFS)
+  target_link_libraries(std-test ${STDLIBFS})
+endif ()


Is it possible to simplify this?

The FS-library name is determined by the version of the C++ Standard Library.
CMake only determine the compiler version.
Clang supports libstdc++ and libcxx.
Intel C++ supports libstdc++ on Linux, libcxx on macOS, and Microsoft STL on Windows.
Therefore, the only way to determine which standard library is actually used is by compiling the code.

The code I wrote is the easiest way I know.

Can this information be derived from CMAKE_CXX_STANDARD_LIBRARIES or CMAKE_CXX_IMPLICIT_LINK_LIBRARIES?

The variable CMAKE_CXX_IMPLICIT_LINK_LIBRARIES allows to detect the standard library name, but not its version.

Example:

GCC-8: CMAKE_CXX_IMPLICIT_LINK_LIBRARIES: stdc++;m;gcc_s;gcc;c;gcc_s;gcc GCC-9: CMAKE_CXX_IMPLICIT_LINK_LIBRARIES: stdc++;m;gcc_s;gcc;c;gcc_s;gcc Clang 13 + libstdc++ (from GCC-11): CMAKE_CXX_IMPLICIT_LINK_LIBRARIES: stdc++;m;gcc_s;gcc;c;gcc_s;gcc Clang 13 + libc++: CMAKE_CXX_IMPLICIT_LINK_LIBRARIES: c++;m;gcc_s;gcc;c;gcc_s;gcc

CMAKE_CXX_STANDARD_LIBRARIES - CMake 3.6+ and empty in most configurations

vitaut · 2022-07-02T14:34:19Z

test/detect-stdfs.cc

+//
+// For the license information refer to format.h.
+
+#include <exception>


This include looks unused.

The macros _GLIBCXX_RELEASE and _LIBCPP_VERSION is defined in standard library header files.

<exception> is the smallest of the standard library header files.

I see. Maybe include <initializer_list> which is slightly cheaper according to https://artificial-mind.net/projects/compile-health/ and add a comment that this is for _GLIBCXX_RELEASE & _LIBCPP_VERSION?

<initializer_list> is C++11.
Specifying the version of the standard will complicate the call to try_compile.

Comment added.

vitaut · 2022-07-02T14:48:56Z

test/CMakeLists.txt

+try_compile(compile_result_unused
+            ${CMAKE_CURRENT_BINARY_DIR}
+            SOURCES ${CMAKE_CURRENT_LIST_DIR}/detect-stdfs.cc
+            CMAKE_FLAGS CMAKE_OSX_ARCHITECTURES=${CMAKE_OSX_ARCHITECTURES}


What is this for?

Compiling detect-stdfs.cc and read compiler output to get fslib info from error message.

I mean specifically the above line that forwards CMAKE_OSX_ARCHITECTURES.

CMAKE_OSX_ARCHITECTURES affects the compiler but I'm not sure if it affects the standard library as well.
Removed it.

Signed-off-by: Vladislav Shchapov <vladislav@shchapov.ru>

vitaut · 2022-07-02T15:34:58Z

Merged, thanks!

vitaut requested changes Jun 30, 2022

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phprus force-pushed the fix-std-1 branch from 30525d5 to 986d1e0 Compare June 30, 2022 15:33

phprus marked this pull request as draft June 30, 2022 15:35

phprus force-pushed the fix-std-1 branch 2 times, most recently from 2581e91 to 1ec4b82 Compare June 30, 2022 16:20

phprus marked this pull request as ready for review June 30, 2022 16:30

phprus changed the title ~~Fix std::variant test on GCC-8.~~ Fix std::variant, std::filesystem::path tests on GCC-8, Clang-7,8. Jun 30, 2022

phprus requested a review from vitaut June 30, 2022 16:58

vitaut reviewed Jul 1, 2022

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phprus force-pushed the fix-std-1 branch from 1ec4b82 to 1009895 Compare July 1, 2022 14:47

vitaut reviewed Jul 2, 2022

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phprus force-pushed the fix-std-1 branch from 1009895 to cf10e09 Compare July 2, 2022 15:04

phprus added 2 commits July 2, 2022 20:19

Fix std::variant, std::filesystem::path tests on GCC-8, Clang-7,8.

cf296cc

Signed-off-by: Vladislav Shchapov <vladislav@shchapov.ru>

New CI: GCC-8 C++17, Clang-8 C++17.

9dba14f

Signed-off-by: Vladislav Shchapov <vladislav@shchapov.ru>

phprus force-pushed the fix-std-1 branch from cf10e09 to 9dba14f Compare July 2, 2022 15:20

vitaut approved these changes Jul 2, 2022

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vitaut merged commit c12b4c0 into fmtlib:master Jul 2, 2022

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Fix std::variant, std::filesystem::path tests on GCC-8, Clang-7,8. #2951

Fix std::variant, std::filesystem::path tests on GCC-8, Clang-7,8. #2951

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vitaut commented Jul 2, 2022

	#ifdef __has_include
	#if __has_include(<variant>) && __cplusplus >= 201703L
	// Otherwise for C++17 and higher use std::variant for UniversalPrinter<>
	// specializations.
	#define GTEST_INTERNAL_HAS_VARIANT 1
	#include <variant>
	namespace testing {

Fix std::variant, std::filesystem::path tests on GCC-8, Clang-7,8. #2951

Fix std::variant, std::filesystem::path tests on GCC-8, Clang-7,8. #2951

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vitaut commented Jul 2, 2022