[Bug libstdc++/91259] Parenthesize requires clauses that contain expressions that are not just a value of type bool

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=91259

--- Comment #5 from Jonathan Wakely <redi at gcc dot gnu.org> ---
(In reply to David Stone from comment #0)
> libstdc++ contains many expressions that are not parenthesized

Many?

> that do not meet these requirements (this was not true of the Concepts TS,
> but as changed as part of standardization). For instance, in <memory>, we
> have `requires ! _Std_pair<_Tp>`.

I'm pretty sure that's the only use of concepts in the whole library.