Should include of quadmath.h in multiprecision/cpp_bin_float.hpp be guarded with ifdef BOOST_MATH_HAS_QUADMATH_H?

From: Martin Jambor (mjambor_at_[hidden])
Date: 2024-07-19 15:55:42

Hello,

because of a bug[1] in GCC 13 and earlier versions, the #include of
quadmath.h in multiprecision/cpp_bin_float.hpp did not fail even when
the header file was not present on the system and compilation succeeded
as long as nothing from the header file was actually needed.

The bug has been fixed in GCC 14 which all of a sudden leads to new
build requirements and failures such as [2].  Examining this build
failure, I noticed that in math/special_functions/fpclassify.hpp (which
is indirectly included from multiprecision/cpp_bin_float.hpp) the
existence of the header file is specifically tested and macro
BOOST_MATH_HAS_QUADMATH_H is defined or not accordingly.

So I wanted to ask the question in the $subject.  Could, or perhaps even
should the include (together with its uses introduced in commit
4911125248bd) be guarded also by BOOST_MATH_HAS_QUADMATH_H and not just
by BOOST_HAS_FLOAT128?

Thank you,

Martin

[1] https://gcc.gnu.org/bugzilla/show_bug.cgi?id=80753
[2] https://bugzilla.opensuse.org/show_bug.cgi?id=1225861#c7