https://gcc.gnu.org/bugzilla/show_bug.cgi?id=89997
--- Comment #6 from Mathias Stearn <redbeard0531 at gmail dot com> --- > I think this is probably not concepts-specific, and just another variant of > PR 49152. Perhaps the busted pretty printer is a general problem, but at least in this case I think the fix may be in concepts code. It looks like the error is generated at https://github.com/gcc-mirror/gcc/blob/16e2427f50c208dfe07d07f18009969502c25dc8/gcc/cp/constraint.cc#L3300 (or the similar call 7 lines lower). Given that gcc already prints the source loc with the invalid expression, I think you can just remove the %qE to improve the diagnostic output. (I don't know the gcc codebase at all, so I could be wrong about this, I just grepped for the string "the required expression")
