Given the conclusion that a painfully large amount of time is spent re-evaluating procedural macros and that this was largely mitigated by adding a cache, it would seem as if the linked discussion about "const" macros on the Rust language design forum is incorrectly analyzing the near-term need for deploying such a feature: they are concentrating on security use cases (which frankly seem a bit dubious to me) or (this one I hadn't heard before but is in the thread) changing where they are packaged (which, to those of us in the peanut gallery wearing our separate compilation hats and prototype fan club hoodies, seems like a far-too-entrenched mistake in Rust's design to bother fixing at this level) whereas being able to safely and automatically know which macros can be cached and which ones can't be (particularly as I'd pray that the big listed use case from the article of a non-const macro--including a file as bytes--either already isn't slow or clearly should be trivially fixed to not be slow) seems to be the real banner feature of having const macros be standardized.