https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100288
--- Comment #5 from Patrick Palka <ppalka at gcc dot gnu.org> --- (In reply to Frank B. Brokken from comment #4) > Dear ppalka at gcc dot gnu.org, you wrote: > > > > https://gcc.gnu.org/bugzilla/show_bug.cgi?id=100288 > > > > Patrick Palka <ppalka at gcc dot gnu.org> changed: > > > > What |Removed |Added > > ---------------------------------------------------------------------------- > > Keywords| |ice-on-invalid-code > > See Also| |https://gcc.gnu.org/bugzill > > | |a/show_bug.cgi?id=99599 > > > > --- Comment #3 from Patrick Palka <ppalka at gcc dot gnu.org> --- > > Agreed, the testcase looks invalid much like PR99599. One workaround for > > avoiding the constraint recursion here would be to change the signature of > > > > template <OstreamInsertable Type> > > inline void operator<<(CSVTabIns &&tab, Type const &value) > > > > to something like > > > > template <std::same_as<std::remove_cvref_t<CSVTabIns>> U, > > OstreamInsertable > > Type> > > inline void operator<<(U &&tab, Type const &value) > > > > so that the constraint OstreamInsertable<Type> is checked on this overload > > only > > if the first argument to << has the expected type. > > > > -- > > You are receiving this mail because: > > You reported the bug. > > Hi Patrick, > > Thanks for your e-mail. > > Since (AFAICS) you directly and only sent your e-mail to me I'm wondering > whether you want me to comment on your e-mail. It's getting kind of late > here, > but I could send a more extensive reply tomorrow. Let me know if that's what > you want. Oh sorry, that was just an automated email for the comment I posted to the bugzilla PR, which gets sent to everyone on the CC list of the PR. I wasn't expecting any sort of reply :) > > I tried your suggestion, and it seems to solve the issue. But at the same > time > it puzzles me why > > template <OstreamInsertable Type> > inline void operator<<(CSVTabIns &&tab, Type const &value) > {} > > won't be instantiated for FMT in > > inline void operator<<(CSVTabIns &tab, FMT::FMTHline hline) > { > tab << (*hline)(1); // insert hline in the next column > } > > when FMT defines FMTHline as 'typedef FMT (*FMTHline)(unsigned)' and > > std::ostream &operator<<(std::ostream &out, FMT const &fmt) > > is declared. I would have expected that > > tab << (*hline)(1); // insert hline in the next column > > would cause the compiler to instantiate > > template <OstreamInsertable Type> > inline void operator<<(CSVTabIns &&tab, Type const &value) > {} > > for Type = FMT. > The compiler does try to instantiate that overload for Type = FMT there, but when checking the constraint OstreamInsertable<FMT> on this overload it needs to resolve the << in requires(std::ostream &out, Type value) { out << value; }; for Type = FMT, during which it considers that same operator<< overload. And CWG2369 says we now first check constraints before non-dependent conversions, but we're in the middle of checking the constraints on this overload, so we enter a constraint loop. > Maybe I'm missing something here? And it's also not something that caused the > compiler's internal error. Yeah, we shouldn't be seeing an internal error even on an invalid testcase. This needs to be fixed.
