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Simplify some binder shifting logic #104927

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Nov 28, 2022
Merged

Simplify some binder shifting logic #104927

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47 changes: 24 additions & 23 deletions compiler/rustc_middle/src/ty/fold.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -407,6 +407,7 @@ where
match *t.kind() {
ty::Bound(debruijn, bound_ty) if debruijn == self.current_index => {
let ty = self.delegate.replace_ty(bound_ty);
debug_assert!(!ty.has_vars_bound_above(ty::INNERMOST));
ty::fold::shift_vars(self.tcx, ty, self.current_index.as_u32())
}
_ if t.has_vars_bound_at_or_above(self.current_index) => t.super_fold_with(self),
Expand Down Expand Up @@ -437,6 +438,7 @@ where
match ct.kind() {
ty::ConstKind::Bound(debruijn, bound_const) if debruijn == self.current_index => {
let ct = self.delegate.replace_const(bound_const, ct.ty());
debug_assert!(!ct.has_vars_bound_above(ty::INNERMOST));
ty::fold::shift_vars(self.tcx, ct, self.current_index.as_u32())
}
_ => ct.super_fold_with(self),
Expand Down Expand Up @@ -697,46 +699,41 @@ impl<'tcx> TypeFolder<'tcx> for Shifter<'tcx> {

fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> {
match *r {
ty::ReLateBound(debruijn, br) => {
if self.amount == 0 || debruijn < self.current_index {
r
} else {
let debruijn = debruijn.shifted_in(self.amount);
let shifted = ty::ReLateBound(debruijn, br);
self.tcx.mk_region(shifted)
}
ty::ReLateBound(debruijn, br) if debruijn >= self.current_index => {
let debruijn = debruijn.shifted_in(self.amount);
let shifted = ty::ReLateBound(debruijn, br);
self.tcx.mk_region(shifted)
}
_ => r,
}
}

fn fold_ty(&mut self, ty: Ty<'tcx>) -> Ty<'tcx> {
match *ty.kind() {
ty::Bound(debruijn, bound_ty) => {
if self.amount == 0 || debruijn < self.current_index {
ty
} else {
let debruijn = debruijn.shifted_in(self.amount);
self.tcx.mk_ty(ty::Bound(debruijn, bound_ty))
}
ty::Bound(debruijn, bound_ty) if debruijn >= self.current_index => {
let debruijn = debruijn.shifted_in(self.amount);
self.tcx.mk_ty(ty::Bound(debruijn, bound_ty))
}

_ => ty.super_fold_with(self),
_ if ty.has_vars_bound_at_or_above(self.current_index) => ty.super_fold_with(self),
_ => ty,
}
}

fn fold_const(&mut self, ct: ty::Const<'tcx>) -> ty::Const<'tcx> {
if let ty::ConstKind::Bound(debruijn, bound_ct) = ct.kind() {
if self.amount == 0 || debruijn < self.current_index {
ct
} else {
let debruijn = debruijn.shifted_in(self.amount);
self.tcx.mk_const(ty::ConstKind::Bound(debruijn, bound_ct), ct.ty())
}
if let ty::ConstKind::Bound(debruijn, bound_ct) = ct.kind()
&& debruijn >= self.current_index
{
let debruijn = debruijn.shifted_in(self.amount);
self.tcx.mk_const(ty::ConstKind::Bound(debruijn, bound_ct), ct.ty())
} else {
ct.super_fold_with(self)
}
}

fn fold_predicate(&mut self, p: ty::Predicate<'tcx>) -> ty::Predicate<'tcx> {
if p.has_vars_bound_at_or_above(self.current_index) { p.super_fold_with(self) } else { p }
}
}

pub fn shift_region<'tcx>(
Expand All @@ -758,5 +755,9 @@ where
{
debug!("shift_vars(value={:?}, amount={})", value, amount);

if amount == 0 || !value.has_escaping_bound_vars() {
return value;
}

value.fold_with(&mut Shifter::new(tcx, amount))
}