diff options
| -rw-r--r-- | src/librustc/ty/fold.rs | 30 |
1 files changed, 25 insertions, 5 deletions
diff --git a/src/librustc/ty/fold.rs b/src/librustc/ty/fold.rs index df8fd102cc5..00fa1a54558 100644 --- a/src/librustc/ty/fold.rs +++ b/src/librustc/ty/fold.rs @@ -243,10 +243,30 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> { where F: FnMut(ty::Region<'tcx>), T: TypeFoldable<'tcx>, { - value.visit_with(&mut RegionVisitor { current_depth: 0, callback }); + value.visit_with(&mut RegionVisitor { + outer_index: ty::DebruijnIndex::INNERMOST, + callback + }); struct RegionVisitor<F> { - current_depth: u32, + /// The index of a binder *just outside* the things we have + /// traversed. If we encounter a bound region bound by this + /// binder or one outer to it, it appears free. Example: + /// + /// ``` + /// for<'a> fn(for<'b> fn(), T) + /// ^ ^ ^ ^ + /// | | | | here, would be shifted in 1 + /// | | | here, would be shifted in 2 + /// | | here, would be INNTERMOST shifted in by 1 + /// | here, initially, binder would be INNERMOST + /// ``` + /// + /// You see that, initially, *any* bound value is free, + /// because we've not traversed any binders. As we pass + /// through a binder, we shift the `outer_index` by 1 to + /// account for the new binder that encloses us. + outer_index: ty::DebruijnIndex, callback: F, } @@ -254,16 +274,16 @@ impl<'a, 'gcx, 'tcx> TyCtxt<'a, 'gcx, 'tcx> { where F : FnMut(ty::Region<'tcx>) { fn visit_binder<T: TypeFoldable<'tcx>>(&mut self, t: &Binder<T>) -> bool { - self.current_depth += 1; + self.outer_index.shift_in(1); t.skip_binder().visit_with(self); - self.current_depth -= 1; + self.outer_index.shift_out(1); false // keep visiting } fn visit_region(&mut self, r: ty::Region<'tcx>) -> bool { match *r { - ty::ReLateBound(debruijn, _) if debruijn.depth <= self.current_depth => { + ty::ReLateBound(debruijn, _) if debruijn < self.outer_index => { /* ignore bound regions */ } _ => (self.callback)(r), |