Add some type-alias-impl-trait regression tests

[rust.git] / src / librustc_ast_lowering / lib.rs

diff --git a/src/librustc_ast_lowering/lib.rs b/src/librustc_ast_lowering/lib.rs
index bc922fa0f55a3f162ee19f9325126354de1e9463..284ede3b4fa1a119d92a81f3794da7c370aa7f2a 100644 (file)
--- a/src/librustc_ast_lowering/lib.rs
+++ b/src/librustc_ast_lowering/lib.rs
@@ -41,7 +41,6 @@
 use rustc_data_structures::captures::Captures;
 use rustc_data_structures::fx::FxHashSet;
 use rustc_data_structures::sync::Lrc;
-use rustc_error_codes::*;
 use rustc_errors::struct_span_err;
 use rustc_hir as hir;
 use rustc_hir::def::{DefKind, Namespace, PartialRes, PerNS, Res};
@@ -1254,6 +1253,8 @@ fn lower_ty_direct(&mut self, t: &Ty, mut itctx: ImplTraitContext<'_, 'hir>) ->
                                 | GenericBound::Trait(ref ty, TraitBoundModifier::MaybeConst) => {
                                     Some(this.lower_poly_trait_ref(ty, itctx.reborrow()))
                                 }
+                                // `?const ?Bound` will cause an error during AST validation
+                                // anyways, so treat it like `?Bound` as compilation proceeds.
                                 GenericBound::Trait(_, TraitBoundModifier::Maybe)
                                 | GenericBound::Trait(_, TraitBoundModifier::MaybeConstMaybe) => {
                                     None
@@ -2301,6 +2302,9 @@ fn lower_trait_bound_modifier(&mut self, f: TraitBoundModifier) -> hir::TraitBou
         match f {
             TraitBoundModifier::None => hir::TraitBoundModifier::None,
             TraitBoundModifier::MaybeConst => hir::TraitBoundModifier::MaybeConst,
+
+            // `MaybeConstMaybe` will cause an error during AST validation, but we need to pick a
+            // placeholder for compilation to proceed.
             TraitBoundModifier::MaybeConstMaybe | TraitBoundModifier::Maybe => {
                 hir::TraitBoundModifier::Maybe
             }