Make TAITs and ATPITs capture late-bound lifetimes in scope

compiler/rustc_ast_lowering/src/item.rs

@@ -275,7 +275,13 @@ impl<'hir> LoweringContext<'_, 'hir> {
                         }
                         Some(ty) => this.lower_ty(
                             ty,
-                            ImplTraitContext::TypeAliasesOpaqueTy { in_assoc_ty: false },
+                            ImplTraitContext::OpaqueTy {
+                                origin: hir::OpaqueTyOrigin::TyAlias {
+                                    parent: this.local_def_id(id),
+                                    in_assoc_ty: false,
+                                },
+                                fn_kind: None,
+                            },
                         ),
                     },
                 );
@@ -936,7 +942,13 @@ impl<'hir> LoweringContext<'_, 'hir> {
                         Some(ty) => {
                             let ty = this.lower_ty(
                                 ty,
-                                ImplTraitContext::TypeAliasesOpaqueTy { in_assoc_ty: true },
+                                ImplTraitContext::OpaqueTy {
+                                    origin: hir::OpaqueTyOrigin::TyAlias {
+                                        parent: this.local_def_id(i.id),
+                                        in_assoc_ty: true,
+                                    },
+                                    fn_kind: None,
+                                },
                             );
                             hir::ImplItemKind::Type(ty)
                         }

compiler/rustc_ast_lowering/src/lib.rs

@@ -265,13 +265,12 @@ enum ImplTraitContext {
     /// Example: `fn foo() -> impl Debug`, where `impl Debug` is conceptually
     /// equivalent to a new opaque type like `type T = impl Debug; fn foo() -> T`.
     ///
-    ReturnPositionOpaqueTy {
-        /// Origin: Either OpaqueTyOrigin::FnReturn or OpaqueTyOrigin::AsyncFn,
+    OpaqueTy {
         origin: hir::OpaqueTyOrigin,
-        fn_kind: FnDeclKind,
+        /// Only used to change the lifetime capture rules, since
+        /// RPITIT captures all in scope, RPIT does not.
+        fn_kind: Option<FnDeclKind>,
     },
-    /// Impl trait in type aliases.
-    TypeAliasesOpaqueTy { in_assoc_ty: bool },
     /// `impl Trait` is unstably accepted in this position.
     FeatureGated(ImplTraitPosition, Symbol),
     /// `impl Trait` is not accepted in this position.
@@ -1075,9 +1074,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                 // Disallow ATB in dyn types
                 if self.is_in_dyn_type {
                     let suggestion = match itctx {
-                        ImplTraitContext::ReturnPositionOpaqueTy { .. }
-                        | ImplTraitContext::TypeAliasesOpaqueTy { .. }
-                        | ImplTraitContext::Universal => {
+                        ImplTraitContext::OpaqueTy { .. } | ImplTraitContext::Universal => {
                             let bound_end_span = constraint
                                 .gen_args
                                 .as_ref()
@@ -1417,24 +1414,14 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
             TyKind::ImplTrait(def_node_id, bounds) => {
                 let span = t.span;
                 match itctx {
-                    ImplTraitContext::ReturnPositionOpaqueTy { origin, fn_kind } => self
-                        .lower_opaque_impl_trait(
-                            span,
-                            origin,
-                            *def_node_id,
-                            bounds,
-                            Some(fn_kind),
-                            itctx,
-                        ),
-                    ImplTraitContext::TypeAliasesOpaqueTy { in_assoc_ty } => self
-                        .lower_opaque_impl_trait(
-                            span,
-                            hir::OpaqueTyOrigin::TyAlias { in_assoc_ty },
-                            *def_node_id,
-                            bounds,
-                            None,
-                            itctx,
-                        ),
+                    ImplTraitContext::OpaqueTy { origin, fn_kind } => self.lower_opaque_impl_trait(
+                        span,
+                        origin,
+                        *def_node_id,
+                        bounds,
+                        fn_kind,
+                        itctx,
+                    ),
                     ImplTraitContext::Universal => {
                         let span = t.span;
 
@@ -1553,9 +1540,14 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
 
         let captured_lifetimes_to_duplicate = match origin {
             hir::OpaqueTyOrigin::TyAlias { .. } => {
-                // in a TAIT like `type Foo<'a> = impl Foo<'a>`, we don't duplicate any
-                // lifetimes, since we don't have the issue that any are late-bound.
-                Vec::new()
+                // type alias impl trait and associated type position impl trait were
+                // decided to capture all in-scope lifetimes, which we collect for
+                // all opaques during resolution.
+                self.resolver
+                    .take_extra_lifetime_params(opaque_ty_node_id)
+                    .into_iter()
+                    .map(|(ident, id, _)| Lifetime { id, ident })
+                    .collect()
             }
             hir::OpaqueTyOrigin::FnReturn(..) => {
                 if matches!(
@@ -1823,9 +1815,9 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                         FnDeclKind::Fn
                         | FnDeclKind::Inherent
                         | FnDeclKind::Trait
-                        | FnDeclKind::Impl => ImplTraitContext::ReturnPositionOpaqueTy {
+                        | FnDeclKind::Impl => ImplTraitContext::OpaqueTy {
                             origin: hir::OpaqueTyOrigin::FnReturn(self.local_def_id(fn_node_id)),
-                            fn_kind: kind,
+                            fn_kind: Some(kind),
                         },
                         FnDeclKind::ExternFn => {
                             ImplTraitContext::Disallowed(ImplTraitPosition::ExternFnReturn)
@@ -1919,9 +1911,9 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                     output,
                     coro,
                     opaque_ty_span,
-                    ImplTraitContext::ReturnPositionOpaqueTy {
+                    ImplTraitContext::OpaqueTy {
                         origin: hir::OpaqueTyOrigin::FnReturn(fn_def_id),
-                        fn_kind,
+                        fn_kind: Some(fn_kind),
                     },
                 );
                 arena_vec![this; bound]

compiler/rustc_ast_lowering/src/path.rs

@@ -423,7 +423,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
             // fn f(_: impl Fn() -> impl Debug) -> impl Fn() -> impl Debug
             // //      disallowed --^^^^^^^^^^        allowed --^^^^^^^^^^
             // ```
-            FnRetTy::Ty(ty) if matches!(itctx, ImplTraitContext::ReturnPositionOpaqueTy { .. }) => {
+            FnRetTy::Ty(ty) if matches!(itctx, ImplTraitContext::OpaqueTy { .. }) => {
                 if self.tcx.features().impl_trait_in_fn_trait_return {
                     self.lower_ty(ty, itctx)
                 } else {

compiler/rustc_borrowck/src/region_infer/opaque_types.rs

@@ -367,14 +367,17 @@ fn check_opaque_type_parameter_valid(
     span: Span,
 ) -> Result<(), ErrorGuaranteed> {
     let opaque_ty_hir = tcx.hir().expect_item(opaque_type_key.def_id);
-    let is_ty_alias = match opaque_ty_hir.expect_opaque_ty().origin {
-        OpaqueTyOrigin::TyAlias { .. } => true,
-        OpaqueTyOrigin::AsyncFn(..) | OpaqueTyOrigin::FnReturn(..) => false,
+    let (parent, is_ty_alias) = match opaque_ty_hir.expect_opaque_ty().origin {
+        OpaqueTyOrigin::TyAlias { parent, .. } => (parent, true),
+        OpaqueTyOrigin::AsyncFn(parent) | OpaqueTyOrigin::FnReturn(parent) => (parent, false),
     };
 
-    let opaque_generics = tcx.generics_of(opaque_type_key.def_id);
+    let parent_generics = tcx.generics_of(parent);
     let mut seen_params: FxIndexMap<_, Vec<_>> = FxIndexMap::default();
-    for (i, arg) in opaque_type_key.args.iter().enumerate() {
+
+    // Only check the parent generics, which will ignore any of the
+    // duplicated lifetime args that come from reifying late-bounds.
+    for (i, arg) in opaque_type_key.args.iter().take(parent_generics.count()).enumerate() {
         if let Err(guar) = arg.error_reported() {
             return Err(guar);
         }
@@ -395,7 +398,7 @@ fn check_opaque_type_parameter_valid(
             seen_params.entry(arg).or_default().push(i);
         } else {
             // Prevent `fn foo() -> Foo<u32>` from being defining.
-            let opaque_param = opaque_generics.param_at(i, tcx);
+            let opaque_param = parent_generics.param_at(i, tcx);
             let kind = opaque_param.kind.descr();
 
             return Err(tcx.dcx().emit_err(NonGenericOpaqueTypeParam {
@@ -409,10 +412,10 @@ fn check_opaque_type_parameter_valid(
 
     for (_, indices) in seen_params {
         if indices.len() > 1 {
-            let descr = opaque_generics.param_at(indices[0], tcx).kind.descr();
+            let descr = parent_generics.param_at(indices[0], tcx).kind.descr();
             let spans: Vec<_> = indices
                 .into_iter()
-                .map(|i| tcx.def_span(opaque_generics.param_at(i, tcx).def_id))
+                .map(|i| tcx.def_span(parent_generics.param_at(i, tcx).def_id))
                 .collect();
             #[allow(rustc::diagnostic_outside_of_impl)]
             #[allow(rustc::untranslatable_diagnostic)]

compiler/rustc_hir/src/hir.rs

@@ -2562,6 +2562,8 @@ pub enum OpaqueTyOrigin {
     AsyncFn(LocalDefId),
     /// type aliases: `type Foo = impl Trait;`
     TyAlias {
+        /// The type alias or associated type parent of the TAIT/ATPIT
+        parent: LocalDefId,
         /// associated types in impl blocks for traits.
         in_assoc_ty: bool,
     },

compiler/rustc_hir_analysis/src/check/check.rs

@@ -339,8 +339,9 @@ fn check_opaque_meets_bounds<'tcx>(
     origin: &hir::OpaqueTyOrigin,
 ) -> Result<(), ErrorGuaranteed> {
     let defining_use_anchor = match *origin {
-        hir::OpaqueTyOrigin::FnReturn(did) | hir::OpaqueTyOrigin::AsyncFn(did) => did,
-        hir::OpaqueTyOrigin::TyAlias { .. } => tcx.impl_trait_parent(def_id),
+        hir::OpaqueTyOrigin::FnReturn(did)
+        | hir::OpaqueTyOrigin::AsyncFn(did)
+        | hir::OpaqueTyOrigin::TyAlias { parent: did, .. } => did,
     };
     let param_env = tcx.param_env(defining_use_anchor);
 
@@ -351,14 +352,14 @@ fn check_opaque_meets_bounds<'tcx>(
     let ocx = ObligationCtxt::new(&infcx);
 
     let args = match *origin {
-        hir::OpaqueTyOrigin::FnReturn(parent) | hir::OpaqueTyOrigin::AsyncFn(parent) => {
-            GenericArgs::identity_for_item(tcx, parent).extend_to(
-                tcx,
-                def_id.to_def_id(),
-                |param, _| tcx.map_rpit_lifetime_to_fn_lifetime(param.def_id.expect_local()).into(),
-            )
-        }
-        hir::OpaqueTyOrigin::TyAlias { .. } => GenericArgs::identity_for_item(tcx, def_id),
+        hir::OpaqueTyOrigin::FnReturn(parent)
+        | hir::OpaqueTyOrigin::AsyncFn(parent)
+        | hir::OpaqueTyOrigin::TyAlias { parent, .. } => GenericArgs::identity_for_item(
+            tcx, parent,
+        )
+        .extend_to(tcx, def_id.to_def_id(), |param, _| {
+            tcx.map_opaque_lifetime_to_parent_lifetime(param.def_id.expect_local()).into()
+        }),
     };
 
     let opaque_ty = Ty::new_opaque(tcx, def_id.to_def_id(), args);

compiler/rustc_hir_analysis/src/collect/predicates_of.rs

@@ -339,7 +339,7 @@ fn compute_bidirectional_outlives_predicates<'tcx>(
     predicates: &mut Vec<(ty::Clause<'tcx>, Span)>,
 ) {
     for param in opaque_own_params {
-        let orig_lifetime = tcx.map_rpit_lifetime_to_fn_lifetime(param.def_id.expect_local());
+        let orig_lifetime = tcx.map_opaque_lifetime_to_parent_lifetime(param.def_id.expect_local());
         if let ty::ReEarlyParam(..) = *orig_lifetime {
             let dup_lifetime = ty::Region::new_early_param(
                 tcx,

compiler/rustc_hir_analysis/src/collect/resolve_bound_vars.rs

@@ -514,38 +514,11 @@ impl<'a, 'tcx> Visitor<'tcx> for BoundVarContext<'a, 'tcx> {
                 // These sorts of items have no lifetime parameters at all.
                 intravisit::walk_item(self, item);
             }
-            hir::ItemKind::OpaqueTy(hir::OpaqueTy {
-                origin: hir::OpaqueTyOrigin::TyAlias { .. },
-                ..
-            }) => {
-                // Opaque types are visited when we visit the
-                // `TyKind::OpaqueDef`, so that they have the lifetimes from
-                // their parent opaque_ty in scope.
-                //
-                // The core idea here is that since OpaqueTys are generated with the impl Trait as
-                // their owner, we can keep going until we find the Item that owns that. We then
-                // conservatively add all resolved lifetimes. Otherwise we run into problems in
-                // cases like `type Foo<'a> = impl Bar<As = impl Baz + 'a>`.
-                let parent_item = self.tcx.hir().get_parent_item(item.hir_id());
-                let resolved_lifetimes: &ResolveBoundVars =
-                    self.tcx.resolve_bound_vars(parent_item);
-                // We need to add *all* deps, since opaque tys may want them from *us*
-                for (&owner, defs) in resolved_lifetimes.defs.iter() {
-                    defs.iter().for_each(|(&local_id, region)| {
-                        self.map.defs.insert(hir::HirId { owner, local_id }, *region);
-                    });
-                }
-                for (&owner, late_bound_vars) in resolved_lifetimes.late_bound_vars.iter() {
-                    late_bound_vars.iter().for_each(|(&local_id, late_bound_vars)| {
-                        self.record_late_bound_vars(
-                            hir::HirId { owner, local_id },
-                            late_bound_vars.clone(),
-                        );
-                    });
-                }
-            }
             hir::ItemKind::OpaqueTy(&hir::OpaqueTy {
-                origin: hir::OpaqueTyOrigin::FnReturn(parent) | hir::OpaqueTyOrigin::AsyncFn(parent),
+                origin:
+                    hir::OpaqueTyOrigin::FnReturn(parent)
+                    | hir::OpaqueTyOrigin::AsyncFn(parent)
+                    | hir::OpaqueTyOrigin::TyAlias { parent, .. },
                 generics,
                 ..
             }) => {
@@ -683,26 +656,7 @@ impl<'a, 'tcx> Visitor<'tcx> for BoundVarContext<'a, 'tcx> {
                 //                                      the opaque_ty generics
                 let opaque_ty = self.tcx.hir().item(item_id);
                 match &opaque_ty.kind {
-                    hir::ItemKind::OpaqueTy(hir::OpaqueTy {
-                        origin: hir::OpaqueTyOrigin::TyAlias { .. },
-                        ..
-                    }) => {
-                        intravisit::walk_ty(self, ty);
-
-                        // Elided lifetimes and late-bound lifetimes (from the parent)
-                        // are not allowed in non-return position impl Trait
-                        let scope = Scope::LateBoundary {
-                            s: &Scope::TraitRefBoundary { s: self.scope },
-                            what: "type alias impl trait",
-                        };
-                        self.with(scope, |this| intravisit::walk_item(this, opaque_ty));
-
-                        return;
-                    }
-                    hir::ItemKind::OpaqueTy(hir::OpaqueTy {
-                        origin: hir::OpaqueTyOrigin::FnReturn(..) | hir::OpaqueTyOrigin::AsyncFn(..),
-                        ..
-                    }) => {}
+                    hir::ItemKind::OpaqueTy(hir::OpaqueTy { origin: _, .. }) => {}
                     i => bug!("`impl Trait` pointed to non-opaque type?? {:#?}", i),
                 };
 

compiler/rustc_hir_analysis/src/collect/type_of.rs

@@ -553,11 +553,11 @@ pub(super) fn type_of_opaque(
         Ok(ty::EarlyBinder::bind(match tcx.hir_node_by_def_id(def_id) {
             Node::Item(item) => match item.kind {
                 ItemKind::OpaqueTy(OpaqueTy {
-                    origin: hir::OpaqueTyOrigin::TyAlias { in_assoc_ty: false },
+                    origin: hir::OpaqueTyOrigin::TyAlias { in_assoc_ty: false, .. },
                     ..
                 }) => opaque::find_opaque_ty_constraints_for_tait(tcx, def_id),
                 ItemKind::OpaqueTy(OpaqueTy {
-                    origin: hir::OpaqueTyOrigin::TyAlias { in_assoc_ty: true },
+                    origin: hir::OpaqueTyOrigin::TyAlias { in_assoc_ty: true, .. },
                     ..
                 }) => opaque::find_opaque_ty_constraints_for_impl_trait_in_assoc_type(tcx, def_id),
                 // Opaque types desugared from `impl Trait`.

compiler/rustc_hir_analysis/src/variance/mod.rs

@@ -125,15 +125,7 @@ fn variance_of_opaque(tcx: TyCtxt<'_>, item_def_id: LocalDefId) -> &[ty::Varianc
 
     // By default, RPIT are invariant wrt type and const generics, but they are bivariant wrt
     // lifetime generics.
-    let variances = std::iter::repeat(ty::Invariant).take(generics.count());
-
-    let mut variances: Vec<_> = match tcx.opaque_type_origin(item_def_id) {
-        rustc_hir::OpaqueTyOrigin::FnReturn(_) | rustc_hir::OpaqueTyOrigin::AsyncFn(_) => {
-            variances.collect()
-        }
-        // But TAIT are invariant for all generics
-        rustc_hir::OpaqueTyOrigin::TyAlias { .. } => return tcx.arena.alloc_from_iter(variances),
-    };
+    let mut variances = vec![ty::Invariant; generics.count()];
 
     // Mark all lifetimes from parent generics as unused (Bivariant).
     // This will be overridden later if required.

compiler/rustc_infer/src/infer/opaque_types/mod.rs

@@ -391,7 +391,7 @@ impl<'tcx> InferCtxt<'tcx> {
             // Anonymous `impl Trait`
             hir::OpaqueTyOrigin::FnReturn(parent) => parent == parent_def_id,
             // Named `type Foo = impl Bar;`
-            hir::OpaqueTyOrigin::TyAlias { in_assoc_ty } => {
+            hir::OpaqueTyOrigin::TyAlias { in_assoc_ty, .. } => {
                 if in_assoc_ty {
                     self.tcx.opaque_types_defined_by(parent_def_id).contains(&def_id)
                 } else {