Selecting GLM_HAS_IF_CONSTEXPR

[ryobg]

GCC 8.x compiles project fixed on C++14

Enabling if constexpr is done by giving priority to the compiler capabilities. Hence, if project has the compiler but is fixed to work on lower standard it will complain. That is, it fails to compile. Example:

../share/glm/gtx/../gtc/../gtc/../gtc/../ext/matrix_transform.inl: In function 'glm::mat<4, 4, T, Q> glm::lookAt(const glm::vec<3, T, Q>&, const glm::vec<3, T, Q>&, const glm::vec<3, T, Q>&)':
../share/glm/detail/setup.hpp:312:31: warning: 'if constexpr' only available with -std=c++17 or -std=gnu++17
 #  define GLM_IF_CONSTEXPR if constexpr
                               ^~~~~~~~~

Reference to the implementation:

#if GLM_HAS_CONSTEXPR
# if (GLM_COMPILER & GLM_COMPILER_CLANG)
#	define GLM_HAS_IF_CONSTEXPR __has_feature(cxx_if_constexpr)
# elif (GLM_COMPILER & GLM_COMPILER_GCC) 
#	define GLM_HAS_IF_CONSTEXPR GLM_COMPILER >= GLM_COMPILER_GCC7
# elif (GLM_LANG & GLM_LANG_CXX17_FLAG)
# 	define GLM_HAS_IF_CONSTEXPR 1
# else
# 	define GLM_HAS_IF_CONSTEXPR 0
# endif
#else
#	define GLM_HAS_IF_CONSTEXPR 0
#endif

#if GLM_HAS_IF_CONSTEXPR
# 	define GLM_IF_CONSTEXPR if constexpr
#else
#	define GLM_IF_CONSTEXPR if
#endif

glm/glm/detail/setup.hpp

Line 297 in fce2abd

#if GLM_HAS_CONSTEXPR

[Groovounet]

This issue should be fixed on master branch for GLM 0.9.9.6 release.

Thanks for reporting,
Christophe