In C++20, we are supposed to use CTAD NTTPs to implement string UDL templates.
Continue to use BOOST_HANA_CONFIG_ENABLE_STRING_UDL to indicate that the string UDL template is available, but enable that macro by default if C++20 is detected.
Compiler support detection is a bit involved, unfortunately, since there isn't a specific feature test macro for it and it appears to have been added in point releases for some compilers.
In C++20, we are supposed to use CTAD NTTPs to implement string UDL templates.
Continue to use BOOST_HANA_CONFIG_ENABLE_STRING_UDL to indicate that the string UDL template is available, but enable that macro by default if C++20 is detected.
Compiler support detection is a bit involved, unfortunately, since there isn't a specific feature test macro for it and it appears to have been added in point releases for some compilers.