Function clean_region_outlives_constraints

fn clean_region_outlives_constraints<'tcx>(
    regions: &RegionConstraintData<'tcx>,
    generics: &'tcx Generics,
) -> ThinVec<WherePredicate>

Clean region outlives constraints to where-predicates.

This is essentially a simplified version of lexical_region_resolve.

However, here we determine what needs to be true in order for an impl to hold. lexical_region_resolve, along with much of the rest of the compiler, is concerned with determining if a given set up constraints / predicates are met, given some starting conditions like user-provided code.

For this reason, it’s easier to perform the calculations we need on our own, rather than trying to make existing inference/solver code do what we want.