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GCI: Reject free const items with trivially unsatisfiable clauses #165153
Description
Uplifted from comment #142293 (comment) (2025).
Not doing so would make adding trait impls (more) breaking. "More" because thanks to 1IR (the "one-impl rule") that's already breaking. Furthermore, const blocks inside fns with trivially unsatisfiable clauses are problematic in quite a similar fashion except that breakages would only ever be post-mono. Related: #165152.
Reproducer
Upstream crate upstream:
pub trait Trait { const THING: (); }
// NOTE: Adding this innocuous-looking impl would break downstream.
//impl Trait for () { const THING: () = (); }Downstream crate downstream:
#![feature(generic_const_items)]
const _: () = {
let _ = <() as upstream::Trait>::THING;
panic!(); // NOTE: Panics if upstream adds the impl
}
where
for<'_delay> (): upstream::Trait;
Activity
[-]Reject free const items with trivially unsatisfiable clauses[/-][+]GCI: Reject free const items with trivially unsatisfiable clauses[/+]