Inherit generics for impl-trait.

compiler/rustc_hir_analysis/src/astconv/mod.rs

@@ -2767,35 +2767,11 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
         let substs = InternalSubsts::for_item(tcx, def_id, |param, _| {
             if let Some(i) = (param.index as usize).checked_sub(generics.parent_count) {
                 // Our own parameters are the resolved lifetimes.
-                if let GenericParamDefKind::Lifetime = param.kind {
-                    if let hir::GenericArg::Lifetime(lifetime) = &lifetimes[i] {
-                        self.ast_region_to_region(lifetime, None).into()
-                    } else {
-                        bug!()
-                    }
-                } else {
-                    bug!()
-                }
+                let GenericParamDefKind::Lifetime { .. } = param.kind else { bug!() };
+                let hir::GenericArg::Lifetime(lifetime) = &lifetimes[i] else { bug!() };
+                self.ast_region_to_region(lifetime, None).into()
             } else {
-                match param.kind {
-                    // For RPIT (return position impl trait), only lifetimes
-                    // mentioned in the impl Trait predicate are captured by
-                    // the opaque type, so the lifetime parameters from the
-                    // parent item need to be replaced with `'static`.
-                    //
-                    // For `impl Trait` in the types of statics, constants,
-                    // locals and type aliases. These capture all parent
-                    // lifetimes, so they can use their identity subst.
-                    GenericParamDefKind::Lifetime
-                        if matches!(
-                            origin,
-                            hir::OpaqueTyOrigin::FnReturn(..) | hir::OpaqueTyOrigin::AsyncFn(..)
-                        ) =>
-                    {
-                        tcx.lifetimes.re_static.into()
-                    }
-                    _ => tcx.mk_param_from_def(param),
-                }
+                tcx.mk_param_from_def(param)
             }
         });
         debug!("impl_trait_ty_to_ty: substs={:?}", substs);
@@ -2972,6 +2948,7 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
         Some(tcx.liberate_late_bound_regions(fn_hir_id.expect_owner().to_def_id(), ty))
     }
 
+    #[instrument(level = "trace", skip(self, generate_err))]
     fn validate_late_bound_regions(
         &self,
         constrained_regions: FxHashSet<ty::BoundRegionKind>,

compiler/rustc_hir_analysis/src/check/check.rs

@@ -240,6 +240,7 @@ fn check_opaque<'tcx>(tcx: TyCtxt<'tcx>, id: hir::ItemId) {
     }
     check_opaque_meets_bounds(tcx, item.owner_id.def_id, substs, span, &origin);
 }
+
 /// Checks that an opaque type does not use `Self` or `T::Foo` projections that would result
 /// in "inheriting lifetimes".
 #[instrument(level = "debug", skip(tcx, span))]
@@ -251,15 +252,19 @@ pub(super) fn check_opaque_for_inheriting_lifetimes<'tcx>(
     let item = tcx.hir().expect_item(def_id);
     debug!(?item, ?span);
 
+    #[derive(Debug)]
     struct FoundParentLifetime;
-    struct FindParentLifetimeVisitor<'tcx>(&'tcx ty::Generics);
+    struct FindParentLifetimeVisitor<'tcx> {
+        tcx: TyCtxt<'tcx>,
+        parent_count: u32,
+    }
     impl<'tcx> ty::visit::TypeVisitor<'tcx> for FindParentLifetimeVisitor<'tcx> {
         type BreakTy = FoundParentLifetime;
 
+        #[instrument(level = "trace", skip(self), ret)]
         fn visit_region(&mut self, r: ty::Region<'tcx>) -> ControlFlow<Self::BreakTy> {
-            debug!("FindParentLifetimeVisitor: r={:?}", r);
             if let ty::ReEarlyBound(ty::EarlyBoundRegion { index, .. }) = *r {
-                if index < self.0.parent_count as u32 {
+                if index < self.parent_count {
                     return ControlFlow::Break(FoundParentLifetime);
                 } else {
                     return ControlFlow::CONTINUE;
@@ -269,6 +274,63 @@ pub(super) fn check_opaque_for_inheriting_lifetimes<'tcx>(
             r.super_visit_with(self)
         }
 
+        #[instrument(level = "trace", skip(self), ret)]
+        fn visit_ty(&mut self, ty: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
+            // We're only interested in types involving regions
+            if !ty.flags().intersects(ty::TypeFlags::HAS_FREE_REGIONS) {
+                return ControlFlow::CONTINUE;
+            }
+
+            match ty.kind() {
+                ty::Closure(_, ref substs) => {
+                    // Skip lifetime parameters of the enclosing item(s)
+
+                    substs.as_closure().tupled_upvars_ty().visit_with(self)?;
+                    substs.as_closure().sig_as_fn_ptr_ty().visit_with(self)?;
+                }
+
+                ty::Generator(_, ref substs, _) => {
+                    // Skip lifetime parameters of the enclosing item(s)
+                    // Also skip the witness type, because that has no free regions.
+
+                    substs.as_generator().tupled_upvars_ty().visit_with(self)?;
+                    substs.as_generator().return_ty().visit_with(self)?;
+                    substs.as_generator().yield_ty().visit_with(self)?;
+                    substs.as_generator().resume_ty().visit_with(self)?;
+                }
+
+                ty::Opaque(def_id, ref substs) => {
+                    // Skip lifetime paramters that are not captures.
+                    let variances = self.tcx.variances_of(*def_id);
+
+                    for (v, s) in std::iter::zip(variances, substs.iter()) {
+                        if *v != ty::Variance::Bivariant {
+                            s.visit_with(self)?;
+                        }
+                    }
+                }
+
+                ty::Projection(proj)
+                    if self.tcx.def_kind(proj.item_def_id) == DefKind::ImplTraitPlaceholder =>
+                {
+                    // Skip lifetime paramters that are not captures.
+                    let variances = self.tcx.variances_of(proj.item_def_id);
+
+                    for (v, s) in std::iter::zip(variances, proj.substs.iter()) {
+                        if *v != ty::Variance::Bivariant {
+                            s.visit_with(self)?;
+                        }
+                    }
+                }
+
+                _ => {
+                    ty.super_visit_with(self)?;
+                }
+            }
+
+            ControlFlow::CONTINUE
+        }
+
         fn visit_const(&mut self, c: ty::Const<'tcx>) -> ControlFlow<Self::BreakTy> {
             if let ty::ConstKind::Unevaluated(..) = c.kind() {
                 // FIXME(#72219) We currently don't detect lifetimes within substs
@@ -291,12 +353,15 @@ pub(super) fn check_opaque_for_inheriting_lifetimes<'tcx>(
         type BreakTy = Ty<'tcx>;
 
         fn visit_ty(&mut self, t: Ty<'tcx>) -> ControlFlow<Self::BreakTy> {
-            debug!("check_opaque_for_inheriting_lifetimes: (visit_ty) t={:?}", t);
+            debug!(?t, "root_visit_ty");
             if t == self.opaque_identity_ty {
                 ControlFlow::CONTINUE
             } else {
-                t.super_visit_with(&mut FindParentLifetimeVisitor(self.generics))
-                    .map_break(|FoundParentLifetime| t)
+                t.visit_with(&mut FindParentLifetimeVisitor {
+                    tcx: self.tcx,
+                    parent_count: self.generics.parent_count as u32,
+                })
+                .map_break(|FoundParentLifetime| t)
             }
         }
     }
@@ -329,14 +394,18 @@ pub(super) fn check_opaque_for_inheriting_lifetimes<'tcx>(
 
     if let ItemKind::OpaqueTy(hir::OpaqueTy {
         origin: hir::OpaqueTyOrigin::AsyncFn(..) | hir::OpaqueTyOrigin::FnReturn(..),
+        in_trait,
         ..
     }) = item.kind
     {
+        let substs = InternalSubsts::identity_for_item(tcx, def_id.to_def_id());
+        let opaque_identity_ty = if in_trait {
+            tcx.mk_projection(def_id.to_def_id(), substs)
+        } else {
+            tcx.mk_opaque(def_id.to_def_id(), substs)
+        };
         let mut visitor = ProhibitOpaqueVisitor {
-            opaque_identity_ty: tcx.mk_opaque(
-                def_id.to_def_id(),
-                InternalSubsts::identity_for_item(tcx, def_id.to_def_id()),
-            ),
+            opaque_identity_ty,
             generics: tcx.generics_of(def_id),
             tcx,
             selftys: vec![],
@@ -345,10 +414,6 @@ pub(super) fn check_opaque_for_inheriting_lifetimes<'tcx>(
             .explicit_item_bounds(def_id)
             .iter()
             .try_for_each(|(predicate, _)| predicate.visit_with(&mut visitor));
-        debug!(
-            "check_opaque_for_inheriting_lifetimes: prohibit_opaque={:?}, visitor.opaque_identity_ty={:?}, visitor.generics={:?}",
-            prohibit_opaque, visitor.opaque_identity_ty, visitor.generics
-        );
 
         if let Some(ty) = prohibit_opaque.break_value() {
             visitor.visit_item(&item);

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

@@ -261,6 +261,7 @@ fn label_msg_span(
     }
 }
 
+#[instrument(level = "trace", skip(tcx))]
 pub fn unexpected_hidden_region_diagnostic<'tcx>(
     tcx: TyCtxt<'tcx>,
     span: Span,

compiler/rustc_infer/src/infer/opaque_types.rs

@@ -332,32 +332,11 @@ impl<'tcx> InferCtxt<'tcx> {
         concrete_ty: Ty<'tcx>,
         span: Span,
     ) {
-        let def_id = opaque_type_key.def_id;
-
-        let tcx = self.tcx;
-
         let concrete_ty = self.resolve_vars_if_possible(concrete_ty);
-
         debug!(?concrete_ty);
 
-        let first_own_region = match self.opaque_ty_origin_unchecked(def_id, span) {
-            hir::OpaqueTyOrigin::FnReturn(..) | hir::OpaqueTyOrigin::AsyncFn(..) => {
-                // We lower
-                //
-                // fn foo<'l0..'ln>() -> impl Trait<'l0..'lm>
-                //
-                // into
-                //
-                // type foo::<'p0..'pn>::Foo<'q0..'qm>
-                // fn foo<l0..'ln>() -> foo::<'static..'static>::Foo<'l0..'lm>.
-                //
-                // For these types we only iterate over `'l0..lm` below.
-                tcx.generics_of(def_id).parent_count
-            }
-            // These opaque type inherit all lifetime parameters from their
-            // parent, so we have to check them all.
-            hir::OpaqueTyOrigin::TyAlias => 0,
-        };
+        let variances = self.tcx.variances_of(opaque_type_key.def_id);
+        debug!(?variances);
 
         // For a case like `impl Foo<'a, 'b>`, we would generate a constraint
         // `'r in ['a, 'b, 'static]` for each region `'r` that appears in the
@@ -370,9 +349,12 @@ impl<'tcx> InferCtxt<'tcx> {
         // type can be equal to any of the region parameters of the
         // opaque type definition.
         let choice_regions: Lrc<Vec<ty::Region<'tcx>>> = Lrc::new(
-            opaque_type_key.substs[first_own_region..]
+            opaque_type_key
+                .substs
                 .iter()
-                .filter_map(|arg| match arg.unpack() {
+                .enumerate()
+                .filter(|(i, _)| variances[*i] == ty::Variance::Invariant)
+                .filter_map(|(_, arg)| match arg.unpack() {
                     GenericArgKind::Lifetime(r) => Some(r),
                     GenericArgKind::Type(_) | GenericArgKind::Const(_) => None,
                 })
@@ -381,6 +363,7 @@ impl<'tcx> InferCtxt<'tcx> {
         );
 
         concrete_ty.visit_with(&mut ConstrainOpaqueTypeRegionVisitor {
+            tcx: self.tcx,
             op: |r| self.member_constraint(opaque_type_key, span, concrete_ty, r, &choice_regions),
         });
     }
@@ -440,11 +423,12 @@ impl<'tcx> InferCtxt<'tcx> {
 //
 // We ignore any type parameters because impl trait values are assumed to
 // capture all the in-scope type parameters.
-struct ConstrainOpaqueTypeRegionVisitor<OP> {
+struct ConstrainOpaqueTypeRegionVisitor<'tcx, OP> {
+    tcx: TyCtxt<'tcx>,
     op: OP,
 }
 
-impl<'tcx, OP> TypeVisitor<'tcx> for ConstrainOpaqueTypeRegionVisitor<OP>
+impl<'tcx, OP> TypeVisitor<'tcx> for ConstrainOpaqueTypeRegionVisitor<'tcx, OP>
 where
     OP: FnMut(ty::Region<'tcx>),
 {
@@ -490,6 +474,31 @@ where
                 substs.as_generator().yield_ty().visit_with(self);
                 substs.as_generator().resume_ty().visit_with(self);
             }
+
+            ty::Opaque(def_id, ref substs) => {
+                // Skip lifetime paramters that are not captures.
+                let variances = self.tcx.variances_of(*def_id);
+
+                for (v, s) in std::iter::zip(variances, substs.iter()) {
+                    if *v != ty::Variance::Bivariant {
+                        s.visit_with(self);
+                    }
+                }
+            }
+
+            ty::Projection(proj)
+                if self.tcx.def_kind(proj.item_def_id) == DefKind::ImplTraitPlaceholder =>
+            {
+                // Skip lifetime paramters that are not captures.
+                let variances = self.tcx.variances_of(proj.item_def_id);
+
+                for (v, s) in std::iter::zip(variances, proj.substs.iter()) {
+                    if *v != ty::Variance::Bivariant {
+                        s.visit_with(self);
+                    }
+                }
+            }
+
             _ => {
                 ty.super_visit_with(self);
             }

compiler/rustc_middle/src/ty/mod.rs

@@ -1338,8 +1338,8 @@ impl<'tcx> OpaqueHiddenType<'tcx> {
             // HACK: The HIR lowering for async fn does not generate
             // any `+ Captures<'x>` bounds for the `impl Future<...>`, so all async fns with lifetimes
             // would now fail to compile. We should probably just make hir lowering fill this in properly.
-            OpaqueTyOrigin::AsyncFn(_) => map.collect(),
-            OpaqueTyOrigin::FnReturn(_) | OpaqueTyOrigin::TyAlias => {
+            OpaqueTyOrigin::FnReturn(_) | OpaqueTyOrigin::AsyncFn(_) => map.collect(),
+            OpaqueTyOrigin::TyAlias => {
                 // Opaque types may only use regions that are bound. So for
                 // ```rust
                 // type Foo<'a, 'b, 'c> = impl Trait<'a> + 'b;

compiler/rustc_middle/src/ty/relate.rs

@@ -170,6 +170,26 @@ pub fn relate_substs_with_variances<'tcx, R: TypeRelation<'tcx>>(
     tcx.mk_substs(params)
 }
 
+#[instrument(level = "trace", skip(relation), ret)]
+fn relate_opaque_item_substs<'tcx, R: TypeRelation<'tcx>>(
+    relation: &mut R,
+    def_id: DefId,
+    a_subst: SubstsRef<'tcx>,
+    b_subst: SubstsRef<'tcx>,
+) -> RelateResult<'tcx, SubstsRef<'tcx>> {
+    let tcx = relation.tcx();
+    let variances = tcx.variances_of(def_id);
+    debug!(?variances);
+
+    let params = iter::zip(a_subst, b_subst).enumerate().map(|(i, (a, b))| {
+        let variance = variances[i];
+        let variance_info = ty::VarianceDiagInfo::default();
+        relation.relate_with_variance(variance, variance_info, a, b)
+    });
+
+    tcx.mk_substs(params)
+}
+
 impl<'tcx> Relate<'tcx> for ty::FnSig<'tcx> {
     fn relate<R: TypeRelation<'tcx>>(
         relation: &mut R,
@@ -561,7 +581,7 @@ pub fn super_relate_tys<'tcx, R: TypeRelation<'tcx>>(
         (&ty::Opaque(a_def_id, a_substs), &ty::Opaque(b_def_id, b_substs))
             if a_def_id == b_def_id =>
         {
-            let substs = relate_substs(relation, a_substs, b_substs)?;
+            let substs = relate_opaque_item_substs(relation, a_def_id, a_substs, b_substs)?;
             Ok(tcx.mk_opaque(a_def_id, substs))
         }