Correctly handle const paths with a qself

Author: camelid

compiler/rustc_ast_lowering/src/lib.rs

@@ -2369,13 +2369,13 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
         } else {
             &anon.value
         };
-        if let ExprKind::Path(qself, path) = &expr.kind
-            // FIXME(min_generic_const_args): we only allow one-segment const paths for now
+        // FIXME(min_generic_const_args): we only allow one-segment const paths for now
+        if let ExprKind::Path(None, path) = &expr.kind
             && path.is_potential_trivial_const_arg()
         {
             let qpath = self.lower_qpath(
                 expr.id,
-                qself,
+                &None,
                 path,
                 ParamMode::Optional,
                 AllowReturnTypeNotation::No,

compiler/rustc_hir_analysis/src/hir_ty_lowering/mod.rs

@@ -2060,7 +2060,7 @@ impl<'tcx> dyn HirTyLowerer<'tcx> + '_ {
             _ => ty::Const::new_error_with_message(
                 tcx,
                 qpath.span(),
-                "Const::lower_const_arg_path: invalid qpath",
+                format!("Const::lower_const_arg_path: invalid qpath {qpath:?}"),
             ),
         }
     }

compiler/rustc_middle/src/ty/consts.rs

@@ -1,3 +1,5 @@
+use std::borrow::Cow;
+
 use either::Either;
 use rustc_data_structures::intern::Interned;
 use rustc_error_messages::MultiSpan;
@@ -141,7 +143,7 @@ impl<'tcx> Const<'tcx> {
     pub fn new_error_with_message<S: Into<MultiSpan>>(
         tcx: TyCtxt<'tcx>,
         span: S,
-        msg: &'static str,
+        msg: impl Into<Cow<'static, str>>,
     ) -> Const<'tcx> {
         let reported = tcx.dcx().span_delayed_bug(span, msg);
         Const::new_error(tcx, reported)