Struct MapAndCompressBoundVars 

struct MapAndCompressBoundVars<'db> {
    tcx: DbInterner<'db>,
    binder: DebruijnIndex,
    still_bound_vars: Vec<BoundVariableKind<'db>>,
    mapping: FxIndexMap<BoundVar, GenericArg<'db>>,
}

Given some where clause like for<'b, 'c> <Self as Trait<'a_identity>>::Gat<'b>: Bound<'c>, the mapping will map 'b back to the GAT’s 'b_identity. Then we need to compress the remaining bound var 'c to index 0.

This folder gives us: for<'c> <Self as Trait<'a_identity>>::Gat<'b_identity>: Bound<'c>, which is sufficient for an item bound for Gat, since all of the GAT’s args are identity.

Fields

tcx: DbInterner<'db>

binder: DebruijnIndex

How deep are we? Makes sure we don’t touch the vars of nested binders.

still_bound_vars: Vec<BoundVariableKind<'db>>

List of bound vars that remain unsubstituted because they were not mentioned in the GAT’s args.

mapping: FxIndexMap<BoundVar, GenericArg<'db>>

Subtle invariant: If the GenericArg is bound, then it should be stored with the debruijn index of INNERMOST so it can be shifted correctly during substitution.

Trait Implementations

impl<'db> TypeFolder<DbInterner<'db>> for MapAndCompressBoundVars<'db>

fn cx(&self) -> DbInterner<'db>

fn fold_binder<T>(&mut self, t: Binder<'db, T>) -> Binder<'db, T>

where Binder<'db, T>: TypeSuperFoldable<DbInterner<'db>>,

fn fold_ty(&mut self, ty: Ty<'db>) -> Ty<'db>

fn fold_region(&mut self, re: Region<'db>) -> Region<'db>

fn fold_const(&mut self, ct: Const<'db>) -> Const<'db>

fn fold_predicate(&mut self, p: Predicate<'db>) -> Predicate<'db>

fn fold_clauses( &mut self, c: <I as Interner>::Clauses, ) -> <I as Interner>::Clauses