Make RPITITs simple cases work when using lower_impl_trait_in_trait_to_assoc_ty

compiler/rustc_hir_analysis/src/astconv/mod.rs

@@ -3049,10 +3049,18 @@ impl<'o, 'tcx> dyn AstConv<'tcx> + 'o {
             }
             &hir::TyKind::OpaqueDef(item_id, lifetimes, in_trait) => {
                 let opaque_ty = tcx.hir().item(item_id);
-                let def_id = item_id.owner_id.to_def_id();
 
                 match opaque_ty.kind {
                     hir::ItemKind::OpaqueTy(hir::OpaqueTy { origin, .. }) => {
+                        let local_def_id = item_id.owner_id.def_id;
+                        // If this is an RPITIT and we are using the new RPITIT lowering scheme, we
+                        // generate the def_id of an associated type for the trait and return as
+                        // type a projection.
+                        let def_id = if in_trait && tcx.lower_impl_trait_in_trait_to_assoc_ty() {
+                            tcx.associated_item_for_impl_trait_in_trait(local_def_id).to_def_id()
+                        } else {
+                            local_def_id.to_def_id()
+                        };
                         self.impl_trait_ty_to_ty(def_id, lifetimes, origin, in_trait)
                     }
                     ref i => bug!("`impl Trait` pointed to non-opaque type?? {:#?}", i),

compiler/rustc_hir_analysis/src/check/compare_impl_item.rs

@@ -830,7 +830,7 @@ impl<'tcx> TypeFolder<TyCtxt<'tcx>> for ImplTraitInTraitCollector<'_, 'tcx> {
 
     fn fold_ty(&mut self, ty: Ty<'tcx>) -> Ty<'tcx> {
         if let ty::Alias(ty::Projection, proj) = ty.kind()
-            && self.interner().def_kind(proj.def_id) == DefKind::ImplTraitPlaceholder
+            && self.interner().is_impl_trait_in_trait(proj.def_id)
         {
             if let Some((ty, _)) = self.types.get(&proj.def_id) {
                 return *ty;
@@ -1995,13 +1995,20 @@ pub(super) fn check_type_bounds<'tcx>(
     let infcx = tcx.infer_ctxt().build();
     let ocx = ObligationCtxt::new(&infcx);
 
-    let impl_ty_span = match tcx.hir().get_by_def_id(impl_ty_def_id) {
-        hir::Node::TraitItem(hir::TraitItem {
-            kind: hir::TraitItemKind::Type(_, Some(ty)),
-            ..
-        }) => ty.span,
-        hir::Node::ImplItem(hir::ImplItem { kind: hir::ImplItemKind::Type(ty), .. }) => ty.span,
-        _ => bug!(),
+    // A synthetic impl Trait for RPITIT desugaring has no HIR, which we currently use to get the
+    // span for an impl's associated type. Instead, for these, use the def_span for the synthesized
+    // associated type.
+    let impl_ty_span = if tcx.opt_rpitit_info(impl_ty.def_id).is_some() {
+        tcx.def_span(impl_ty_def_id)
+    } else {
+        match tcx.hir().get_by_def_id(impl_ty_def_id) {
+            hir::Node::TraitItem(hir::TraitItem {
+                kind: hir::TraitItemKind::Type(_, Some(ty)),
+                ..
+            }) => ty.span,
+            hir::Node::ImplItem(hir::ImplItem { kind: hir::ImplItemKind::Type(ty), .. }) => ty.span,
+            _ => bug!(),
+        }
     };
     let assumed_wf_types = ocx.assumed_wf_types(param_env, impl_ty_span, impl_ty_def_id);
 

compiler/rustc_hir_analysis/src/collect/item_bounds.rs

@@ -3,7 +3,7 @@ use crate::astconv::AstConv;
 use rustc_hir as hir;
 use rustc_infer::traits::util;
 use rustc_middle::ty::subst::InternalSubsts;
-use rustc_middle::ty::{self, TyCtxt};
+use rustc_middle::ty::{self, ImplTraitInTraitData, Ty, TyCtxt};
 use rustc_span::def_id::DefId;
 use rustc_span::Span;
 
@@ -58,17 +58,10 @@ fn opaque_type_bounds<'tcx>(
     tcx: TyCtxt<'tcx>,
     opaque_def_id: DefId,
     ast_bounds: &'tcx [hir::GenericBound<'tcx>],
+    item_ty: Ty<'tcx>,
     span: Span,
-    in_trait: bool,
 ) -> &'tcx [(ty::Predicate<'tcx>, Span)] {
     ty::print::with_no_queries!({
-        let substs = InternalSubsts::identity_for_item(tcx, opaque_def_id);
-        let item_ty = if in_trait {
-            tcx.mk_projection(opaque_def_id, substs)
-        } else {
-            tcx.mk_opaque(opaque_def_id, substs)
-        };
-
         let icx = ItemCtxt::new(tcx, opaque_def_id);
         let mut bounds = icx.astconv().compute_bounds(item_ty, ast_bounds);
         // Opaque types are implicitly sized unless a `?Sized` bound is found
@@ -83,7 +76,18 @@ pub(super) fn explicit_item_bounds(
     tcx: TyCtxt<'_>,
     def_id: DefId,
 ) -> &'_ [(ty::Predicate<'_>, Span)] {
-    let hir_id = tcx.hir().local_def_id_to_hir_id(def_id.expect_local());
+    // If the def_id is about an RPITIT, delegate explicit_item_bounds to the opaque_def_id that
+    // generated the synthesized associate type.
+    let rpitit_info = if let Some(ImplTraitInTraitData::Trait { opaque_def_id, .. }) =
+        tcx.opt_rpitit_info(def_id)
+    {
+        Some(opaque_def_id)
+    } else {
+        None
+    };
+
+    let bounds_def_id = rpitit_info.unwrap_or(def_id);
+    let hir_id = tcx.hir().local_def_id_to_hir_id(bounds_def_id.expect_local());
     match tcx.hir().get(hir_id) {
         hir::Node::TraitItem(hir::TraitItem {
             kind: hir::TraitItemKind::Type(bounds, _),
@@ -94,7 +98,15 @@ pub(super) fn explicit_item_bounds(
             kind: hir::ItemKind::OpaqueTy(hir::OpaqueTy { bounds, in_trait, .. }),
             span,
             ..
-        }) => opaque_type_bounds(tcx, def_id, bounds, *span, *in_trait),
+        }) => {
+            let substs = InternalSubsts::identity_for_item(tcx, def_id);
+            let item_ty = if *in_trait || rpitit_info.is_some() {
+                tcx.mk_projection(def_id, substs)
+            } else {
+                tcx.mk_opaque(def_id, substs)
+            };
+            opaque_type_bounds(tcx, bounds_def_id, bounds, item_ty, *span)
+        }
         _ => bug!("item_bounds called on {:?}", def_id),
     }
 }

compiler/rustc_hir_analysis/src/collect/type_of.rs

@@ -9,7 +9,8 @@ use rustc_middle::ty::print::with_forced_trimmed_paths;
 use rustc_middle::ty::subst::InternalSubsts;
 use rustc_middle::ty::util::IntTypeExt;
 use rustc_middle::ty::{
-    self, IsSuggestable, Ty, TyCtxt, TypeFolder, TypeSuperFoldable, TypeVisitableExt,
+    self, ImplTraitInTraitData, IsSuggestable, Ty, TyCtxt, TypeFolder, TypeSuperFoldable,
+    TypeVisitableExt,
 };
 use rustc_span::symbol::Ident;
 use rustc_span::{Span, DUMMY_SP};
@@ -244,6 +245,24 @@ fn get_path_containing_arg_in_pat<'hir>(
 }
 
 pub(super) fn type_of(tcx: TyCtxt<'_>, def_id: DefId) -> ty::EarlyBinder<Ty<'_>> {
+    // If we are computing `type_of` the synthesized associated type for an RPITIT in the impl
+    // side, use `collect_return_position_impl_trait_in_trait_tys` to infer the value of the
+    // associated type in the impl.
+    if let Some(ImplTraitInTraitData::Impl { fn_def_id, .. }) = tcx.opt_rpitit_info(def_id) {
+        match tcx.collect_return_position_impl_trait_in_trait_tys(fn_def_id) {
+            Ok(map) => {
+                let assoc_item = tcx.associated_item(def_id);
+                return ty::EarlyBinder(map[&assoc_item.trait_item_def_id.unwrap()]);
+            }
+            Err(_) => {
+                return ty::EarlyBinder(tcx.ty_error_with_message(
+                    DUMMY_SP,
+                    "Could not collect return position impl trait in trait tys",
+                ));
+            }
+        }
+    }
+
     let def_id = def_id.expect_local();
     use rustc_hir::*;
 

compiler/rustc_metadata/src/rmeta/encoder.rs

@@ -1104,7 +1104,7 @@ fn should_encode_const(def_kind: DefKind) -> bool {
 // We only encode impl trait in trait when using `lower-impl-trait-in-trait-to-assoc-ty` unstable
 // option.
 fn should_encode_fn_impl_trait_in_trait<'tcx>(tcx: TyCtxt<'tcx>, def_id: DefId) -> bool {
-    if tcx.sess.opts.unstable_opts.lower_impl_trait_in_trait_to_assoc_ty
+    if tcx.lower_impl_trait_in_trait_to_assoc_ty()
         && let Some(assoc_item) = tcx.opt_associated_item(def_id)
         && assoc_item.container == ty::AssocItemContainer::TraitContainer
         && assoc_item.kind == ty::AssocKind::Fn

compiler/rustc_middle/src/query/mod.rs

@@ -1324,6 +1324,7 @@ rustc_queries! {
     /// might want to use `reveal_all()` method to change modes.
     query param_env(def_id: DefId) -> ty::ParamEnv<'tcx> {
         desc { |tcx| "computing normalized predicates of `{}`", tcx.def_path_str(def_id) }
+        feedable
     }
 
     /// Like `param_env`, but returns the `ParamEnv` in `Reveal::All` mode.

compiler/rustc_middle/src/ty/context.rs

@@ -2439,6 +2439,18 @@ impl<'tcx> TyCtxt<'tcx> {
     pub fn trait_solver_next(self) -> bool {
         self.sess.opts.unstable_opts.trait_solver == rustc_session::config::TraitSolver::Next
     }
+
+    pub fn lower_impl_trait_in_trait_to_assoc_ty(self) -> bool {
+        self.sess.opts.unstable_opts.lower_impl_trait_in_trait_to_assoc_ty
+    }
+
+    pub fn is_impl_trait_in_trait(self, def_id: DefId) -> bool {
+        if self.lower_impl_trait_in_trait_to_assoc_ty() {
+            self.def_kind(def_id) == DefKind::AssocTy && self.opt_rpitit_info(def_id).is_some()
+        } else {
+            self.def_kind(def_id) == DefKind::ImplTraitPlaceholder
+        }
+    }
 }
 
 impl<'tcx> TyCtxtAt<'tcx> {

compiler/rustc_passes/src/dead.rs

@@ -243,6 +243,12 @@ impl<'tcx> MarkSymbolVisitor<'tcx> {
                 continue;
             }
 
+            // Avoid accessing the HIR for the synthesized associated type generated for RPITITs.
+            if self.tcx.opt_rpitit_info(id).is_some() {
+                self.live_symbols.insert(id);
+                continue;
+            }
+
             // in the case of tuple struct constructors we want to check the item, not the generated
             // tuple struct constructor function
             let id = self.struct_constructors.get(&id).copied().unwrap_or(id);

compiler/rustc_ty_utils/src/assoc.rs

@@ -23,7 +23,7 @@ fn associated_item_def_ids(tcx: TyCtxt<'_>, def_id: DefId) -> &[DefId] {
     let item = tcx.hir().expect_item(def_id.expect_local());
     match item.kind {
         hir::ItemKind::Trait(.., ref trait_item_refs) => {
-            if tcx.sess.opts.unstable_opts.lower_impl_trait_in_trait_to_assoc_ty {
+            if tcx.lower_impl_trait_in_trait_to_assoc_ty() {
                 // We collect RPITITs for each trait method's return type and create a
                 // corresponding associated item using associated_items_for_impl_trait_in_trait
                 // query.
@@ -54,7 +54,7 @@ fn associated_item_def_ids(tcx: TyCtxt<'_>, def_id: DefId) -> &[DefId] {
             }
         }
         hir::ItemKind::Impl(ref impl_) => {
-            if tcx.sess.opts.unstable_opts.lower_impl_trait_in_trait_to_assoc_ty {
+            if tcx.lower_impl_trait_in_trait_to_assoc_ty() {
                 // We collect RPITITs for each trait method's return type, on the impl side too and
                 // create a corresponding associated item using
                 // associated_items_for_impl_trait_in_trait query.
@@ -302,9 +302,6 @@ fn associated_item_for_impl_trait_in_trait(
     // There are no inferred outlives for the synthesized associated type.
     trait_assoc_ty.inferred_outlives_of(&[]);
 
-    // FIXME implement this.
-    trait_assoc_ty.explicit_item_bounds(&[]);
-
     local_def_id
 }
 
@@ -316,11 +313,12 @@ fn impl_associated_item_for_impl_trait_in_trait(
     trait_assoc_def_id: LocalDefId,
     impl_fn_def_id: LocalDefId,
 ) -> LocalDefId {
-    let impl_def_id = tcx.local_parent(impl_fn_def_id);
+    let impl_local_def_id = tcx.local_parent(impl_fn_def_id);
+    let impl_def_id = impl_local_def_id.to_def_id();
 
     // FIXME fix the span, we probably want the def_id of the return type of the function
     let span = tcx.def_span(impl_fn_def_id);
-    let impl_assoc_ty = tcx.at(span).create_def(impl_def_id, DefPathData::ImplTraitAssocTy);
+    let impl_assoc_ty = tcx.at(span).create_def(impl_local_def_id, DefPathData::ImplTraitAssocTy);
 
     let local_def_id = impl_assoc_ty.def_id();
     let def_id = local_def_id.to_def_id();
@@ -345,13 +343,53 @@ fn impl_associated_item_for_impl_trait_in_trait(
         fn_has_self_parameter: false,
     });
 
+    // Copy param_env of the containing function. The synthesized associated type doesn't have
+    // extra predicates to assume.
+    impl_assoc_ty.param_env(tcx.param_env(impl_fn_def_id));
+
     // Copy impl_defaultness of the containing function.
     impl_assoc_ty.impl_defaultness(tcx.impl_defaultness(impl_fn_def_id));
 
-    // Copy generics_of the trait's associated item.
-    // FIXME: This is not correct, in particular the parent is going to be wrong. So we would need
-    // to copy from trait_assoc_def_id and adjust things.
-    impl_assoc_ty.generics_of(tcx.generics_of(trait_assoc_def_id).clone());
+    // Copy generics_of the trait's associated item but the impl as the parent.
+    impl_assoc_ty.generics_of({
+        let trait_assoc_generics = tcx.generics_of(trait_assoc_def_id);
+        let trait_assoc_parent_count = trait_assoc_generics.parent_count;
+        let mut params = trait_assoc_generics.params.clone();
+
+        let parent_generics = tcx.generics_of(impl_def_id);
+        let parent_count = parent_generics.parent_count + parent_generics.params.len();
+
+        let mut impl_fn_params = tcx.generics_of(impl_fn_def_id).params.clone();
+
+        for param in &mut params {
+            param.index = param.index + parent_count as u32 + impl_fn_params.len() as u32
+                - trait_assoc_parent_count as u32;
+        }
+
+        impl_fn_params.extend(params);
+        params = impl_fn_params;
+
+        let param_def_id_to_index =
+            params.iter().map(|param| (param.def_id, param.index)).collect();
+
+        ty::Generics {
+            parent: Some(impl_def_id),
+            parent_count,
+            params,
+            param_def_id_to_index,
+            has_self: false,
+            has_late_bound_regions: trait_assoc_generics.has_late_bound_regions,
+        }
+    });
+
+    // There are no predicates for the synthesized associated type.
+    impl_assoc_ty.explicit_predicates_of(ty::GenericPredicates {
+        parent: Some(impl_def_id),
+        predicates: &[],
+    });
+
+    // There are no inferred outlives for the synthesized associated type.
+    impl_assoc_ty.inferred_outlives_of(&[]);
 
     local_def_id
 }

compiler/rustc_ty_utils/src/ty.rs

@@ -3,8 +3,8 @@ use rustc_hir as hir;
 use rustc_hir::def::DefKind;
 use rustc_index::bit_set::BitSet;
 use rustc_middle::ty::{
-    self, Binder, EarlyBinder, Predicate, PredicateKind, ToPredicate, Ty, TyCtxt,
-    TypeSuperVisitable, TypeVisitable, TypeVisitor,
+    self, Binder, EarlyBinder, ImplTraitInTraitData, Predicate, PredicateKind, ToPredicate, Ty,
+    TyCtxt, TypeSuperVisitable, TypeVisitable, TypeVisitor,
 };
 use rustc_session::config::TraitSolver;
 use rustc_span::def_id::{DefId, CRATE_DEF_ID};
@@ -117,6 +117,15 @@ fn adt_sized_constraint(tcx: TyCtxt<'_>, def_id: DefId) -> &[Ty<'_>] {
 
 /// See `ParamEnv` struct definition for details.
 fn param_env(tcx: TyCtxt<'_>, def_id: DefId) -> ty::ParamEnv<'_> {
+    // When computing the param_env of an RPITIT, copy param_env of the containing function. The
+    // synthesized associated type doesn't have extra predicates to assume.
+    let def_id =
+        if let Some(ImplTraitInTraitData::Trait { fn_def_id, .. }) = tcx.opt_rpitit_info(def_id) {
+            fn_def_id
+        } else {
+            def_id
+        };
+
     // Compute the bounds on Self and the type parameters.
     let ty::InstantiatedPredicates { mut predicates, .. } =
         tcx.predicates_of(def_id).instantiate_identity(tcx);

tests/ui/impl-trait/in-trait/new-lowering-strategy/simple-impl-trait.rs

@@ -0,0 +1,17 @@
+// check-pass
+// compile-flags: -Zlower-impl-trait-in-trait-to-assoc-ty
+
+#![feature(return_position_impl_trait_in_trait)]
+#![allow(incomplete_features)]
+
+trait Foo {
+    fn foo() -> impl Sized;
+}
+
+impl Foo for String {
+    fn foo() -> i32 {
+        22
+    }
+}
+
+fn main() {}