You might consider restricting the first character, which must exist, to
[a-zA-Z] to avoid things getting confused by a leading `-`.
Might also consider . and : for otherwise meaningless namespacing
conventions, similar to the meaningless ones for modules?


On Mon, Oct 14, 2024 at 4:05 PM Barry Revzin via SG15 <sg15_at_[hidden]>
wrote:

> Hey Tooling Study Group,
>
> I have this paper, P2758 (latest currently:
> https://www.open-std.org/jtc1/sc22/wg21/docs/papers/2024/p2758r3.html),
> which proposes low-level utilities for emitting messages during constant
> evaluation time.
>
> Those messages have three kinds (print, warning, and error) and can also
> be tagged. The intent of the tagging is to give the user the kind of
> control typically reserved for the compiler. That is, the format library
> can diagnose something with:
>
> std::constexpr_warning("format-too-many-args", "Format string consumed {}
> arguments but {} were provided.", current_arg, total);
>
> And that'll emit a compiler warning that maybe can be explicitly enabled
> (with some flag like -Wformat-too-many-args) or disabled (with some flag
> like -Wno-format-too-many-args). And possibly likewise with #pragmas for
> local blocks. Of course the actual mechanism is implementation-defined and
> it's likely the flags won't be exactly that so that they won't clash with
> actual implementation warnings.
>
> Evolution was happy with this proposal, but wanted you all to take a look
> at it for its use of tagging to make sure that this is a viable path. Right
> now, the paper's restriction on tagging is that it only contains,
> basically, a-z, A-Z, 0-9, an underscore, or a hyphen — although it
> presently also allows empty strings, which I'll change in a subsequent
> revision. That restriction avoids having to really deal with unicode stuff,
> while also matching the set of characters currently used in compiler flags
> anyway, so doesn't seem like it's cutting off anything useful to me.
>
> Thanks in advance for the feedback,
>
> Barry
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