[chowells]

You've described three different features with three different sets of semantics. Which set of semantics is honored? Unknown!

This is not software engineering. This is an appeal to faith. Software engineering requires precise semantics, not whatever the compiler feels like doing. You can't even declare that this feature has no semantics, because it actually introduces a vector for UB. This is the sort of "feature" that should not be in any language selling itself as an improved C. It would be far better to reduce the scope to the point where the feature can have precise semantics.

[tialaramex]

> Which set of semantics is honored?

Typically it's configurable. For example C++ 26 seems to be intending you'll pick a compiler flag to say if you want its do-nothing semantics, or its "tell me about the problem and press on" semantics or just exit immediately and report that. They're not intending (in the standard at least) to have the assume semantic because that is, as you'd expect, controversial. Likewise more fine-grained configuration they're hoping will be taken up as a vendor extension.

My understanding is that C3 will likely offer the coarse configuration as part of their ordinary fast versus safe settings. Do I think that's a good idea? No, but that's definitely not "Unknown".

[fc417fc802]

Any idea how the situation is handled where third party code was written to expect a certain semantic? Is this just one more rough edge to watch out for when integrating something?

[dnautics]

not enforced for any given implementation is hardly "unknown". presumably the tin comes with a label saying what's inside