Re-enable ConstArgKind::Path lowering by default

...and remove the `const_arg_path` feature gate as a result. It was only
a stopgap measure to fix the regression that the new lowering introduced
(which should now be fixed by this PR).

compiler/rustc_ast_lowering/src/asm.rs

@@ -220,9 +220,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
  let parent_def_id = self.current_def_id_parent;
  let node_id = self.next_node_id();
  // HACK(min_generic_const_args): see lower_anon_const
- if !self.tcx.features().const_arg_path
- || !expr.is_potential_trivial_const_arg()
- {
+ if !expr.is_potential_trivial_const_arg() {
  self.create_def(
  parent_def_id,
  node_id,

compiler/rustc_ast_lowering/src/expr.rs

@@ -387,7 +387,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
  let node_id = self.next_node_id();
 
  // HACK(min_generic_const_args): see lower_anon_const
- if !self.tcx.features().const_arg_path || !arg.is_potential_trivial_const_arg() {
+ if !arg.is_potential_trivial_const_arg() {
  // Add a definition for the in-band const def.
  self.create_def(parent_def_id, node_id, kw::Empty, DefKind::AnonConst, f.span);
  }

compiler/rustc_ast_lowering/src/lib.rs

@@ -2335,7 +2335,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
  span: Span,
  ) -> &'hir hir::ConstArg<'hir> {
  let ct_kind = match res {
- Res::Def(DefKind::ConstParam, _) if self.tcx.features().const_arg_path => {
+ Res::Def(DefKind::ConstParam, _) => {
  let qpath = self.lower_qpath(
  ty_id,
  &None,
@@ -2410,8 +2410,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
  self.resolver.get_partial_res(expr.id).and_then(|partial_res| partial_res.full_res());
  debug!("res={:?}", maybe_res);
  // FIXME(min_generic_const_args): for now we only lower params to ConstArgKind::Path
- if self.tcx.features().const_arg_path
- && let Some(res) = maybe_res
+ if let Some(res) = maybe_res
  && let Res::Def(DefKind::ConstParam, _) = res
  && let ExprKind::Path(qself, path) = &expr.kind
  {
@@ -2442,7 +2441,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
  /// See [`hir::ConstArg`] for when to use this function vs
  /// [`Self::lower_anon_const_to_const_arg`].
  fn lower_anon_const_to_anon_const(&mut self, c: &AnonConst) -> &'hir hir::AnonConst {
- if self.tcx.features().const_arg_path && c.value.is_potential_trivial_const_arg() {
+ if c.value.is_potential_trivial_const_arg() {
  // HACK(min_generic_const_args): see DefCollector::visit_anon_const
  // Over there, we guess if this is a bare param and only create a def if
  // we think it's not. However we may can guess wrong (see there for example)

compiler/rustc_feature/src/unstable.rs

@@ -193,8 +193,6 @@ declare_features! (
  (unstable, anonymous_lifetime_in_impl_trait, "1.63.0", None),
  /// Allows identifying the `compiler_builtins` crate.
  (internal, compiler_builtins, "1.13.0", None),
- /// Gating for a new desugaring of const arguments of usages of const parameters
- (internal, const_arg_path, "1.81.0", None),
  /// Allows writing custom MIR
  (internal, custom_mir, "1.65.0", None),
  /// Outputs useful `assert!` messages

compiler/rustc_middle/src/ty/consts.rs

@@ -302,13 +302,7 @@ impl<'tcx> Const<'tcx> {
  ),
  ) = expr.kind
  {
- if tcx.features().const_arg_path {
- span_bug!(
- expr.span,
- "try_from_lit: received const param which shouldn't be possible"
- );
- }
- return Some(Const::from_param(tcx, qpath, expr.hir_id));
+ span_bug!(expr.span, "try_from_lit: received const param which shouldn't be possible");
  };
 
  let lit_input = match expr.kind {

compiler/rustc_resolve/src/def_collector.rs

@@ -347,9 +347,7 @@ impl<'a, 'b, 'tcx> visit::Visitor<'a> for DefCollector<'a, 'b, 'tcx> {
  }
 
  fn visit_anon_const(&mut self, constant: &'a AnonConst) {
- if self.resolver.tcx.features().const_arg_path
- && constant.value.is_potential_trivial_const_arg()
- {
+ if constant.value.is_potential_trivial_const_arg() {
  // HACK(min_generic_const_args): don't create defs for anon consts if we think they will
  // later be turned into ConstArgKind::Path's. because this is before resolve is done, we
  // may accidentally identify a construction of a unit struct as a param and not create a

compiler/rustc_span/src/symbol.rs

@@ -599,7 +599,6 @@ symbols! {
  conservative_impl_trait,
  console,
  const_allocate,
- const_arg_path,
  const_async_blocks,
  const_closures,
  const_compare_raw_pointers,