Remap impl-trait lifetimes on HIR instead of AST lowering.

Author: cjgillot

compiler/rustc_ast_lowering/src/lib.rs

@@ -830,7 +830,7 @@ impl<'tcx> MirBorrowckCtxt<'_, '_, '_, 'tcx> {
     ///
     /// [`OpaqueDef`]: hir::TyKind::OpaqueDef
     fn get_future_inner_return_ty(&self, hir_ty: &'tcx hir::Ty<'tcx>) -> &'tcx hir::Ty<'tcx> {
-        let hir::TyKind::OpaqueDef(opaque_ty, _) = hir_ty.kind else {
+        let hir::TyKind::OpaqueDef(opaque_ty) = hir_ty.kind else {
             span_bug!(
                 hir_ty.span,
                 "lowered return type of async fn is not OpaqueDef: {:?}",

compiler/rustc_ast_lowering/src/lifetime_collector.rs

@@ -2610,7 +2610,6 @@ impl<'hir> Ty<'hir> {
             }
             TyKind::Tup(tys) => tys.iter().any(Self::is_suggestable_infer_ty),
             TyKind::Ptr(mut_ty) | TyKind::Ref(_, mut_ty) => mut_ty.ty.is_suggestable_infer_ty(),
-            TyKind::OpaqueDef(_, generic_args) => are_suggestable_generic_args(generic_args),
             TyKind::Path(QPath::TypeRelative(ty, segment)) => {
                 ty.is_suggestable_infer_ty() || are_suggestable_generic_args(segment.args().args)
             }
@@ -2729,19 +2728,8 @@ pub struct BareFnTy<'hir> {
 pub struct OpaqueTy<'hir> {
     pub hir_id: HirId,
     pub def_id: LocalDefId,
-    pub generics: &'hir Generics<'hir>,
     pub bounds: GenericBounds<'hir>,
     pub origin: OpaqueTyOrigin,
-    /// Return-position impl traits (and async futures) must "reify" any late-bound
-    /// lifetimes that are captured from the function signature they originate from.
-    ///
-    /// This is done by generating a new early-bound lifetime parameter local to the
-    /// opaque which is instantiated in the function signature with the late-bound
-    /// lifetime.
-    ///
-    /// This mapping associated a captured lifetime (first parameter) with the new
-    /// early-bound lifetime that was generated for the opaque.
-    pub lifetime_mapping: &'hir [(&'hir Lifetime, LocalDefId)],
     /// Whether the opaque is a return-position impl trait (or async future)
     /// originating from a trait method. This makes it so that the opaque is
     /// lowered as an associated type.
@@ -2837,7 +2825,7 @@ pub enum TyKind<'hir> {
     /// possibly parameters) that are actually bound on the `impl Trait`.
     ///
     /// The last parameter specifies whether this opaque appears in a trait definition.
-    OpaqueDef(&'hir OpaqueTy<'hir>, &'hir [GenericArg<'hir>]),
+    OpaqueDef(&'hir OpaqueTy<'hir>),
     /// A trait object type `Bound1 + Bound2 + Bound3`
     /// where `Bound` is a trait or a lifetime.
     TraitObject(
@@ -3959,7 +3947,6 @@ impl<'hir> Node<'hir> {
             | Node::TraitItem(TraitItem { generics, .. })
             | Node::ImplItem(ImplItem { generics, .. }) => Some(generics),
             Node::Item(item) => item.kind.generics(),
-            Node::OpaqueTy(opaque) => Some(opaque.generics),
             _ => None,
         }
     }

compiler/rustc_borrowck/src/diagnostics/region_name.rs

@@ -896,9 +896,8 @@ pub fn walk_ty<'v, V: Visitor<'v>>(visitor: &mut V, typ: &'v Ty<'v>) -> V::Resul
         TyKind::Path(ref qpath) => {
             try_visit!(visitor.visit_qpath(qpath, typ.hir_id, typ.span));
         }
-        TyKind::OpaqueDef(opaque, lifetimes) => {
+        TyKind::OpaqueDef(opaque) => {
             try_visit!(visitor.visit_opaque_ty(opaque));
-            walk_list!(visitor, visit_generic_arg, lifetimes);
         }
         TyKind::Array(ref ty, ref length) => {
             try_visit!(visitor.visit_ty(ty));
@@ -1188,18 +1187,8 @@ pub fn walk_poly_trait_ref<'v, V: Visitor<'v>>(
 }
 
 pub fn walk_opaque_ty<'v, V: Visitor<'v>>(visitor: &mut V, opaque: &'v OpaqueTy<'v>) -> V::Result {
-    let &OpaqueTy {
-        hir_id,
-        def_id: _,
-        generics,
-        bounds,
-        origin: _,
-        lifetime_mapping: _,
-        in_trait: _,
-        span: _,
-    } = opaque;
+    let &OpaqueTy { hir_id, def_id: _, bounds, origin: _, in_trait: _, span: _ } = opaque;
     try_visit!(visitor.visit_id(hir_id));
-    try_visit!(walk_generics(visitor, generics));
     walk_list!(visitor, visit_param_bound, bounds);
     V::Result::output()
 }

compiler/rustc_hir/src/hir.rs

@@ -1395,7 +1395,7 @@ fn trait_def(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::TraitDef {
     }
 }
 
-#[instrument(level = "debug", skip(tcx))]
+#[instrument(level = "debug", skip(tcx), ret)]
 fn fn_sig(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::EarlyBinder<'_, ty::PolyFnSig<'_>> {
     use rustc_hir::Node::*;
     use rustc_hir::*;

compiler/rustc_hir/src/intravisit.rs

@@ -456,6 +456,21 @@ pub(super) fn generics_of(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::Generics {
         });
     }
 
+    if let Node::OpaqueTy(&hir::OpaqueTy { .. }) = node {
+        assert!(own_params.is_empty());
+
+        let lifetimes = tcx.opaque_captured_lifetimes(def_id);
+        debug!(?lifetimes);
+
+        own_params.extend(lifetimes.iter().map(|&(_, param)| ty::GenericParamDef {
+            name: tcx.item_name(param.to_def_id()),
+            index: next_index(),
+            def_id: param.to_def_id(),
+            pure_wrt_drop: false,
+            kind: ty::GenericParamDefKind::Lifetime,
+        }))
+    }
+
     let param_def_id_to_index =
         own_params.iter().map(|param| (param.def_id, param.index)).collect();
 

compiler/rustc_hir_analysis/src/collect.rs

@@ -334,13 +334,6 @@ fn gather_explicit_predicates_of(tcx: TyCtxt<'_>, def_id: LocalDefId) -> ty::Gen
     // We create bi-directional Outlives predicates between the original
     // and the duplicated parameter, to ensure that they do not get out of sync.
     if let Node::OpaqueTy(..) = node {
-        let opaque_ty_node = tcx.parent_hir_node(hir_id);
-        let Node::Ty(&hir::Ty { kind: TyKind::OpaqueDef(_, lifetimes), .. }) = opaque_ty_node
-        else {
-            bug!("unexpected {opaque_ty_node:?}")
-        };
-        debug!(?lifetimes);
-
         compute_bidirectional_outlives_predicates(tcx, &generics.own_params, &mut predicates);
         debug!(?predicates);
     }