Rollup merge of #129383 - cjgillot:opaque-noremap, r=compiler-errors,petrochenkov

Remap impl-trait lifetimes on HIR instead of AST lowering

Current AST->HIR lowering goes out of its way to remap lifetimes for opaque types. This is complicated and leaks into upstream and downstream code.

This PR stops trying to be clever during lowering, and prefers to do this remapping during the HIR->ty lowering. The remapping computation easily fits into the bound var resolution code. Its result can be used in by `generics_of` and `hir_ty_lowering::new_opaque` to add the proper parameters and arguments.

See an example on the doc for query `opaque_captured_lifetimes`.

Based on #129244

Fixes #125249
Fixes #126850

cc `@compiler-errors` `@spastorino`
r? `@petrochenkov`

Author: workingjubilee

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

@@ -2627,7 +2627,6 @@ 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)
             }
@@ -2746,19 +2745,8 @@ 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)],
     pub span: Span,
 }
 
@@ -2861,12 +2849,7 @@ pub enum TyKind<'hir> {
     /// Type parameters may be stored in each `PathSegment`.
     Path(QPath<'hir>),
     /// An opaque type definition itself. This is only used for `impl Trait`.
-    ///
-    /// The generic argument list contains the lifetimes (and in the future
-    /// 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(&'hir [PolyTraitRef<'hir>], &'hir Lifetime, TraitObjectSyntax),
@@ -3991,7 +3974,6 @@ 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));
@@ -1188,10 +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: _, span: _ } =
-        opaque;
+    let &OpaqueTy { hir_id, def_id: _, bounds, origin: _, 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

@@ -1302,7 +1302,7 @@ 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

@@ -426,6 +426,21 @@ 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

@@ -329,13 +329,6 @@ 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);
     }