Why not just a generic compiler diagnostic message mechanism?

[[diagnostic(level, msg)]]
Where level in { info, warn, error }

Relieve the compiler of the need to care about the reason.

This would allow an easy progression from notification to potential build failure to certain build failure.

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On Thu, Mar 11, 2021 at 3:14 PM, Carlos ORyan via Std-Proposals <std-proposals@lists.isocpp.org> wrote:
Hi,

I would like to propose an attribute [[experimental(msg)]], with similar semantics to [[deprecated(msg)]].  Even on (or specially on) stable libraries the  developers may wish to introduce a new type or function to their libraries, but are uncertain if this is the final form the addition would take.

Some users of such libraries may want to receive a diagnostic when using experimental features. Other (more adventurous types) may be Okay with adopting not-quite-fully-baked features. Abusing [[deprecated(msg)]] for this purpose almost works, but has some clear disadvantages:

- It is obviously the wrong annotation, a casual reader may draw the wrong conclusion.
- The compiler diagnostics typically include the word "deprecated" which is confusing. 
- Users of the library may wish to receive diagnostics about deprecated features, but may be Okay with using new experimental features.

Having a new attribute would obviate these problems and give library developers a path to introduce new functionality, with sufficient diagnostics for folks that prefer to avoid them.


Regards,

--
Carlos O'Ryan
// -fno-exceptions delenda est