Currently it is not checked that operator in_in_result<II1, II2>() SFINAEs away properly
Reviewed By: ldionne, #libc
Spies: libcxx-commits
Differential Revision: https://reviews.llvm.org/D117517
This needs a proper solution in a follow-up. The issue is that the
Standard defines conversions between `in_out_result` classes with
different template types as just `return {in, out};`. Because the
expression uses list initialization, it will fail to compile if the
conversion happens to be narrowing -- which is probably unintended.
Surprisingly, this error wasn't caught by the CI.
Differential Revision: https://reviews.llvm.org/D117089