> I actually don’t see how this is any more beneficial than the existing no_panic macro

I think looking at the caveats listed in the no_panic docs should give you some ideas as to how a "proper" no_panic effect could improve on the macro.

Furthermore, a "proper" effect system should make working with effects nicer in general - for instance, right now writing functions that work independently of effects is not particularly ergonomic.

> The vast majority of rust programs don’t need such validation.

I think you also need to consider the niches which Rust wants to target. Rust is intended to be usable for very low-level/foundational/etc. niches where being able to track such effects is handy, if not outright required, so adding such support would be unblocking Rust for use in places the devs want it to be usable in.

> And for those that do, the Ferrocene project is maintaining a downstream fork of the compiler where this kind of feature would be more appropriate.

Given this bit from the Ferrocene website:

> Ferrocene is downstream from Rust

> It works with existing Rust infrastructure and the only changes made in the code were to cover testing requirements of ISO 26262, IEC 61508 and IEC 62304 qualification. All fixes are reported upstream for constant improvement.

I would suspect that such changes would be out of scope for the Ferrocene fork because that fork is more intended to be a qualified/certified Rust more than Rust + completely novel extensions.

> The compiler itself provides a powerful api via build.rs and proc macros which let downstream maintainers build their desired customization.

Given the complexity of the features listed this feels tantamount to asking each individual consumer to make their own fork which doesn't seem very likely to attract much interest. IIRC async even started off like that (i.e., using a macro), but that was painful enough and async thought to be useful enough to be promoted to a language feature.

I'm curious to what extent one can implement the described features using just build.rs/proc macros in the first place without effectively writing a new compiler.