https://gcc.gnu.org/bugzilla/show_bug.cgi?id=103626
--- Comment #4 from Arsen Arsenović <arsen at aarsen dot me> --- (In reply to Jonathan Wakely from comment #3) > I don't think we need to add the #error to every header. For a start, users > never include the bits/* headers directly, and if they do, it's their > problem. So we only need to mark the standard headers as hosted-only. And if > we add it to <iosfwd>, that already covers a large number of them, because > they include that. My thinking behind doing that was that it'd make includes transitively carry a requirement on hosted, so that if some header is meant to be freestanding, but depends on a hosted header, that could be detected (and that could probably be a testcase).