Implement the `min_const_fn` feature gate
cc @RalfJung @eddyb
r? @Centril
implements the feature gate for #53555
I added a hack so the `const_fn` feature gate also enables the `min_const_fn` feature gate. This ensures that nightly users of `const_fn` don't have to touch their code at all.
The `min_const_fn` checks are run first, and if they succeeded, the `const_fn` checks are run additionally to ensure we didn't miss anything.
Fix promotion stability hole in old borrowck
r? @nikomatsakis
I screwed up the promotion stability checks. Big time. They were basically nonexistant. We had tests for it. I also screwed up said tests. This is in stable already :(
Basically stability checks of promotion only worked if you tried to use a const fn defined in the same crate.
cc @eddyb
During the sanity check, we keep track of the path we are below in a `Vec`. We
avoid cloning that `Vec` unless we hit a pointer indirection. The `String`
representation is only computed when validation actually fails.
