Patch 1.15.1 breaks build for MSVC v140

[csandmann]

Issue

Since version 1.15.1 the MSVC v140 build breaks with the attached errors.

cl : Command line warning D9002: ignoring unknown option '/Zc:__cplusplus' [spdlog\build\spdlog.vcxproj]
  spdlog.cpp
spdlog\include\spdlog\fmt\bundled\base.h(743): error C2327: 'fmt::v11::basic_specs::data_': is not a type name, static, or enumerator [spdlog\build\spdlog.vcxproj]
spdlog\include\spdlog\fmt\bundled\base.h(743): error C2065: 'data_': undeclared identifier [spdlog\build\spdlog.vcxproj]
spdlog\include\spdlog\fmt\bundled\base.h(743): error C2338:  [spdlog\build\spdlog.vcxproj]
  stdout_sinks.cpp
spdlog\include\spdlog\fmt\bundled\base.h(743): error C2327: 'fmt::v11::basic_specs::data_': is not a type name, static, or enumerator [spdlog\build\spdlog.vcxproj]
spdlog\include\spdlog\fmt\bundled\base.h(743): error C2065: 'data_': undeclared identifier [spdlog\build\spdlog.vcxproj]
spdlog\include\spdlog\fmt\bundled\base.h(743): error C2338:  [spdlog\build\spdlog.vcxproj]
  color_sinks.cpp
spdlog\include\spdlog\fmt\bundled\base.h(743): error C2327: 'fmt::v11::basic_specs::data_': is not a type name, static, or enumerator [spdlog\build\spdlog.vcxproj]
spdlog\include\spdlog\fmt\bundled\base.h(743): error C2065: 'data_': undeclared identifier [spdlog\build\spdlog.vcxproj]
spdlog\include\spdlog\fmt\bundled\base.h(743): error C2338:  [spdlog\build\spdlog.vcxproj]
  file_sinks.cpp
spdlog\include\spdlog\fmt\bundled\base.h(743): error C2327: 'fmt::v11::basic_specs::data_': is not a type name, static, or enumerator [spdlog\build\spdlog.vcxproj]
spdlog\include\spdlog\fmt\bundled\base.h(743): error C2065: 'data_': undeclared identifier [spdlog\build\spdlog.vcxproj]
spdlog\include\spdlog\fmt\bundled\base.h(743): error C2338:  [spdlog\build\spdlog.vcxproj]
  async.cpp
spdlog\include\spdlog\fmt\bundled\base.h(743): error C2327: 'fmt::v11::basic_specs::data_': is not a type name, static, or enumerator [spdlog\build\spdlog.vcxproj]
spdlog\include\spdlog\fmt\bundled\base.h(743): error C2065: 'data_': undeclared identifier [spdlog\build\spdlog.vcxproj]
spdlog\include\spdlog\fmt\bundled\base.h(743): error C2338:  [spdlog\build\spdlog.vcxproj]
  cfg.cpp
spdlog\include\spdlog\fmt\bundled\base.h(743): error C2327: 'fmt::v11::basic_specs::data_': is not a type name, static, or enumerator [spdlog\build\spdlog.vcxproj]
spdlog\include\spdlog\fmt\bundled\base.h(743): error C2065: 'data_': undeclared identifier [spdlog\build\spdlog.vcxproj]
spdlog\include\spdlog\fmt\bundled\base.h(743): error C2338:  [spdlog\build\spdlog.vcxproj]
  bundled_fmtlib_format.cpp
spdlog\include\spdlog\fmt\bundled\base.h(743): error C2327: 'fmt::v11::basic_specs::data_': is not a type name, static, or enumerator [spdlog\build\spdlog.vcxproj]
spdlog\include\spdlog\fmt\bundled\base.h(743): error C2065: 'data_': undeclared identifier [spdlog\build\spdlog.vcxproj]
spdlog\include\spdlog\fmt\bundled\base.h(743): error C2338:  [spdlog\build\spdlog.vcxproj]

Details

• spdlog v1.15.0 builds without issues
• Latest visual studio toolchain (v1942) builds without issues
• When removing the static_assert(...) in line 743, a new error appears when compiling example.cpp (details in comments)

System

Visual Studio 2022 (17.12.4) with extension MSVC v140 - VS 2015 C++-Buildtools (v14.00)

Steps to reproduce

1. git checkout v1.15.1
2. cmake -T v140 -S . -B build/ && cmake --build build/

[tt4g]

Not recognizing data_ is obviously not right.

spdlog/include/spdlog/fmt/bundled/base.h

Lines 742 to 743 in f355b3d

	unsigned data_ = 1 << fill_size_shift;
	static_assert(sizeof(data_) * CHAR_BIT >= 18, "");

Maybe the source code has been changed?

[csandmann]

Yes, the file has changed significantly since the last release: The entire class basic_specs is new. The build works fine though with the latest toolset (v1942)

If I remove the static_assert(...), a new error appears, this time, when when building the example project.

------ Build started: Project: example, Configuration: Release x64 ------
2>example.cpp
2>spdlog\include\spdlog\fmt\bundled\base.h(2208): error C2664: 'fmt::v11::detail::value<Context>::value(fmt::v11::detail::value<Context> &&)': cannot convert argument 1 from 'spdlog::details::dump_info<std::_Vector_const_iterator<std::_Vector_val<std::_Simple_types<char>>>>' to 'const fmt::v11::detail::named_arg_info<Char> *'
2>        with
2>        [
2>            Context=fmt::v11::context
2>        ]
2>        and
2>        [
2>            Char=char
2>        ]

Note sure what the implication of this is: Maybe its a configuration issue, there is a lot of #ifdefs going on in the beginning.

[tt4g]

Maybe the source code has been changed?

The above comment was meant to ask you to check if data_ is defined in the source code saved on your machine.
However, it is most likely a bug in MSVC since it can be built with another version toolset.

Since this source code was copied from the fmt repository, you should request that it be fixed in the fmt repository.
I recommend moving the issue to the fmt repository.

[csandmann]

Thanks for the quick reaction. I was not aware that this part of the code comes from a different repository. I confirmed the latest version of fmtlib indeed comes with the same problem. I created a new issue fmtlib/fmt#4346

[csandmann]

The linked upstream issue in fmtlib was closed due to this being a likely compiler issue. Do you see more than the following options to go forward?

1. Try to fix fmtlib
2. Downgrade fmtlib to version compatible with vc140
3. Drop support for vc140

[tt4g]

If it is a compiler bug, the second solution would be the only way.
If fmtlib is fixed, the third solution can be used.

[tt4g]

For the second solution, you can define a CMake variable SPDLOG_FMT_EXTERNAL=ON and use the old version of fmt.

spdlog/CMakeLists.txt

Lines 91 to 92 in f355b3d

	option(SPDLOG_FMT_EXTERNAL "Use external fmt library instead of bundled" OFF)
	option(SPDLOG_FMT_EXTERNAL_HO "Use external fmt header-only library instead of bundled" OFF)

[csandmann]

I just confirmed this solution works. Following the discussion in the linked issue of fmtlib, the first bad commit is fmtlib/fmt@761d35f. This means that fmtlib 11.0.2 is the last working version for MSVC v140.

Build spdlog with fmtlib 11.0.2 and MSVC v140

Step 1: Build fmtlib

git checkout 11.0.2
cmake -S . -B build -T v140
cmake --build ./build --config Release
cmake --install ./build --prefix ${FMT_INSTALL_DIR}

Step 2: Build spdlog with external fmtlib

cmake -S . -B build/ -T v140 -DSPDLOG_FMT_EXTERNAL=ON -Dfmt_DIR="${FMT_INSTALL_DIR}\lib\cmake\fmt"
cmake --build build/ --config Release
cmake --install ./build --prefix ${SPDLOG_INSTALL_DIR}

Thanks for your help!