error: friend declaration with a constraint that depends on an enclosing template parameter must be a definition

[intractabilis]

https://github.com/tzlaine/parser/blob/4cea9c03d6baf8165a21162e66be4f99ec85b529/include/boost/parser/detail/text/transcode_view.hpp#L178 Clang 18.1.4 with -std=gnu++23 complains here that this friend function must be defined, not just declared. It seems correct according to 13.7.5 Friends.