Different use_constexpr definitions in spdlog and fmt causes compile time error in NVCC (and possibly other compilers)

[ShujianQian]

Description

When calling logger.trace() in an .cu file compiled using nvcc, I get the following compile time error:

spdlog/common.h:351:30: error: call to non-‘constexpr’ function ‘const T* fmt::v9::detail::buffer<T>::data() const [with T = char]’
  351 |     return spdlog::string_view_t{buf.data(), buf.size()};
      |                      ~~~~~~~~^~

Cause

The to_string_view utility function is declared as SPDLOG_CONSTEXPR_FUNC. The functions calls fmt::v9::detail::buffer::data() which is declared as FMT_CONSTEXPR. However, FMT_CONSTEXPR has different conditions than SPDLOG_CONSTEXPR_FUNC and is defined to be empty for NVCC, leading to the data() function not declared as constexpr and thus causing the error.

Fix

Adding the same condition to the definition of SPDLOG_CONSTEXPR_FUNC fixes the error. However, the two definitions need to be kept in sync in future changes.

Another potential fix is to declare the to_string_view functions as inline instead of constexpr.

[tt4g]

PR is welcome.

[gabime]

Which version of spdlog?

[ShujianQian]

This is introduced in commit 4f800773 and is included in v1.12.0 and in the current v1.x branch.

[cartoonist]

I came across the same issue using nvcc 11.4 and gcc 10.5.0. PR #2859 fixed it for me (spdlog v1.11.0). Thanks @ShujianQian for the PR!