Check item bounds for projection clause wellformedness #150662
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adwinwhite wants to merge 1 commit intorust-lang:mainfrom
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Check item bounds for projection clause wellformedness #150662adwinwhite wants to merge 1 commit intorust-lang:mainfrom
adwinwhite wants to merge 1 commit intorust-lang:mainfrom
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☔ The latest upstream changes (presumably #150844) made this pull request unmergeable. Please resolve the merge conflicts. |
lcnr
reviewed
Jan 20, 2026
| region_mapping: FxHashMap<ty::Region<'tcx>, ty::Region<'tcx>>, | ||
| const_mapping: FxHashMap<ty::Const<'tcx>, ty::Const<'tcx>>, | ||
| } | ||
| impl<'tcx> PredicateArgFolder<'tcx> { |
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how does this folder differ from whatever.instantiate(projection.projection_term.args)? 🤔
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This folder additionally maps identity projection alias to the rhs type of the projection: Self::Assoc -> projection.term. It's needed to apply the item bounds on projection.term.
E.g.
trait Trait<T> {
type Assoc: Bound<T>;
}
fn function<T, U, I>()
where
// We need to transform `Self::Assoc: Bound<T>` into `U: Bound<I>`.
// With instantiating alone, the result would be `T::Assoc: Bound<I>`, which is pointless
// as `AliasBound` candidate already covers this.
T: Trait<I, Assoc = U>
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Experiment for #149283.
There're some fatal regressions.
Preparing to run crater to find out the range of breakages.
r? @ghost