Make TypeFolder::fold_* return Result

Author: LeSeulArtichaut

compiler/rustc_middle/src/ty/fold.rs

@@ -46,8 +46,8 @@ use std::ops::ControlFlow;
 ///
 /// To implement this conveniently, use the derive macro located in `rustc_macros`.
 pub trait TypeFoldable<'tcx>: fmt::Debug + Clone {
- fn super_fold_with<F: TypeFolder<'tcx>>(self, folder: &mut F) -> Self;
- fn fold_with<F: TypeFolder<'tcx>>(self, folder: &mut F) -> Self {
+ fn super_fold_with<F: TypeFolder<'tcx>>(self, folder: &mut F) -> Result<Self, F::Error>;
+ fn fold_with<F: TypeFolder<'tcx>>(self, folder: &mut F) -> Result<Self, F::Error> {
  self.super_fold_with(folder)
  }
 
@@ -193,32 +193,43 @@ impl TypeFoldable<'tcx> for hir::Constness {
 /// identity fold, it should invoke `foo.fold_with(self)` to fold each
 /// sub-item.
 pub trait TypeFolder<'tcx>: Sized {
+ type Error = !;
+
  fn tcx<'a>(&'a self) -> TyCtxt<'tcx>;
 
- fn fold_binder<T>(&mut self, t: Binder<'tcx, T>) -> Binder<'tcx, T>
+ fn fold_binder<T>(&mut self, t: Binder<'tcx, T>) -> Result<Binder<'tcx, T>, Self::Error>
  where
  T: TypeFoldable<'tcx>,
  {
  t.super_fold_with(self)
  }
 
- fn fold_ty(&mut self, t: Ty<'tcx>) -> Ty<'tcx> {
+ fn fold_ty(&mut self, t: Ty<'tcx>) -> Result<Ty<'tcx>, Self::Error> {
  t.super_fold_with(self)
  }
 
- fn fold_region(&mut self, r: ty::Region<'tcx>) -> ty::Region<'tcx> {
+ fn fold_region(&mut self, r: ty::Region<'tcx>) -> Result<ty::Region<'tcx>, Self::Error> {
  r.super_fold_with(self)
  }
 
- fn fold_const(&mut self, c: &'tcx ty::Const<'tcx>) -> &'tcx ty::Const<'tcx> {
+ fn fold_const(
+ &mut self,
+ c: &'tcx ty::Const<'tcx>,
+ ) -> Result<&'tcx ty::Const<'tcx>, Self::Error> {
  c.super_fold_with(self)
  }
 
- fn fold_predicate(&mut self, p: ty::Predicate<'tcx>) -> ty::Predicate<'tcx> {
+ fn fold_predicate(
+ &mut self,
+ p: ty::Predicate<'tcx>,
+ ) -> Result<ty::Predicate<'tcx>, Self::Error> {
  p.super_fold_with(self)
  }
 
- fn fold_mir_const(&mut self, c: mir::ConstantKind<'tcx>) -> mir::ConstantKind<'tcx> {
+ fn fold_mir_const(
+ &mut self,
+ c: mir::ConstantKind<'tcx>,
+ ) -> Result<mir::ConstantKind<'tcx>, Self::Error> {
  bug!("most type folders should not be folding MIR datastructures: {:?}", c)
  }
 }