diff options
Diffstat (limited to 'compiler/rustc_trait_selection/src/traits/normalize.rs')
| -rw-r--r-- | compiler/rustc_trait_selection/src/traits/normalize.rs | 13 |
1 files changed, 8 insertions, 5 deletions
diff --git a/compiler/rustc_trait_selection/src/traits/normalize.rs b/compiler/rustc_trait_selection/src/traits/normalize.rs index 7551ac5aa97..afa72a79848 100644 --- a/compiler/rustc_trait_selection/src/traits/normalize.rs +++ b/compiler/rustc_trait_selection/src/traits/normalize.rs @@ -260,11 +260,14 @@ impl<'a, 'b, 'tcx> TypeFolder<TyCtxt<'tcx>> for AssocTypeNormalizer<'a, 'b, 'tcx } ty::Projection if !data.has_escaping_bound_vars() => { - // This branch is *mostly* just an optimization: when we don't - // have escaping bound vars, we don't need to replace them with - // placeholders (see branch below). *Also*, we know that we can - // register an obligation to *later* project, since we know - // there won't be bound vars there. + // When we don't have escaping bound vars we can normalize ambig aliases + // to inference variables (done in `normalize_projection_ty`). This would + // be wrong if there were escaping bound vars as even if we instantiated + // the bound vars with placeholders, we wouldn't be able to map them back + // after normalization succeeded. + // + // Also, as an optimization: when we don't have escaping bound vars, we don't + // need to replace them with placeholders (see branch below). let data = data.fold_with(self); let normalized_ty = project::normalize_projection_ty( self.selcx, |