Give return-position impl traits in trait a (synthetic) name to avoid name collisions with new lowering strategy

compiler/rustc_hir/src/definitions.rs

@@ -281,7 +281,7 @@ pub enum DefPathData {
     /// An `impl Trait` type node.
     ImplTrait,
     /// `impl Trait` generated associated type node.
-    ImplTraitAssocTy,
+    ImplTraitAssocTy(Symbol),
 }
 
 impl Definitions {
@@ -402,11 +402,11 @@ impl DefPathData {
     pub fn get_opt_name(&self) -> Option<Symbol> {
         use self::DefPathData::*;
         match *self {
-            TypeNs(name) | ValueNs(name) | MacroNs(name) | LifetimeNs(name) => Some(name),
-
-            // We use this name when collecting `ModChild`s.
-            // FIXME this could probably be removed with some refactoring to the name resolver.
-            ImplTraitAssocTy => Some(kw::Empty),
+            TypeNs(name)
+            | ValueNs(name)
+            | MacroNs(name)
+            | LifetimeNs(name)
+            | ImplTraitAssocTy(name) => Some(name),
 
             Impl | ForeignMod | CrateRoot | Use | GlobalAsm | ClosureExpr | Ctor | AnonConst
             | ImplTrait => None,
@@ -416,9 +416,11 @@ impl DefPathData {
     pub fn name(&self) -> DefPathDataName {
         use self::DefPathData::*;
         match *self {
-            TypeNs(name) | ValueNs(name) | MacroNs(name) | LifetimeNs(name) => {
-                DefPathDataName::Named(name)
-            }
+            TypeNs(name)
+            | ValueNs(name)
+            | MacroNs(name)
+            | LifetimeNs(name)
+            | ImplTraitAssocTy(name) => DefPathDataName::Named(name),
             // Note that this does not show up in user print-outs.
             CrateRoot => DefPathDataName::Anon { namespace: kw::Crate },
             Impl => DefPathDataName::Anon { namespace: kw::Impl },
@@ -428,7 +430,7 @@ impl DefPathData {
             ClosureExpr => DefPathDataName::Anon { namespace: sym::closure },
             Ctor => DefPathDataName::Anon { namespace: sym::constructor },
             AnonConst => DefPathDataName::Anon { namespace: sym::constant },
-            ImplTrait | ImplTraitAssocTy => DefPathDataName::Anon { namespace: sym::opaque },
+            ImplTrait => DefPathDataName::Anon { namespace: sym::opaque },
         }
     }
 }

compiler/rustc_metadata/src/rmeta/encoder.rs

@@ -1044,7 +1044,13 @@ fn should_encode_type(tcx: TyCtxt<'_>, def_id: LocalDefId, def_kind: DefKind) ->
             let assoc_item = tcx.associated_item(def_id);
             match assoc_item.container {
                 ty::AssocItemContainer::ImplContainer => true,
-                ty::AssocItemContainer::TraitContainer => assoc_item.defaultness(tcx).has_value(),
+                // FIXME(-Zlower-impl-trait-in-trait-to-assoc-ty) always encode RPITITs,
+                // since we need to be able to "project" from an RPITIT associated item
+                // to an opaque when installing the default projection predicates in
+                // default trait methods with RPITITs.
+                ty::AssocItemContainer::TraitContainer => {
+                    assoc_item.defaultness(tcx).has_value() || assoc_item.opt_rpitit_info.is_some()
+                }
             }
         }
         DefKind::TyParam => {

compiler/rustc_symbol_mangling/src/typeid/typeid_itanium_cxx_abi.rs

@@ -396,7 +396,7 @@ fn encode_ty_name(tcx: TyCtxt<'_>, def_id: DefId) -> String {
             hir::definitions::DefPathData::CrateRoot
             | hir::definitions::DefPathData::Use
             | hir::definitions::DefPathData::GlobalAsm
-            | hir::definitions::DefPathData::ImplTraitAssocTy
+            | hir::definitions::DefPathData::ImplTraitAssocTy(_)
             | hir::definitions::DefPathData::MacroNs(..)
             | hir::definitions::DefPathData::LifetimeNs(..) => {
                 bug!("encode_ty_name: unexpected `{:?}`", disambiguated_data.data);

compiler/rustc_symbol_mangling/src/v0.rs

@@ -792,7 +792,7 @@ impl<'tcx> Printer<'tcx> for &mut SymbolMangler<'tcx> {
             | DefPathData::Use
             | DefPathData::GlobalAsm
             | DefPathData::Impl
-            | DefPathData::ImplTraitAssocTy
+            | DefPathData::ImplTraitAssocTy(_)
             | DefPathData::MacroNs(_)
             | DefPathData::LifetimeNs(_) => {
                 bug!("symbol_names: unexpected DefPathData: {:?}", disambiguated_data.data)

compiler/rustc_ty_utils/src/assoc.rs

@@ -1,10 +1,11 @@
+use rustc_data_structures::fx::FxIndexSet;
 use rustc_hir as hir;
 use rustc_hir::def::DefKind;
 use rustc_hir::def_id::{DefId, DefIdMap, LocalDefId};
 use rustc_hir::definitions::DefPathData;
 use rustc_hir::intravisit::{self, Visitor};
 use rustc_middle::ty::{self, ImplTraitInTraitData, InternalSubsts, TyCtxt};
-use rustc_span::symbol::kw;
+use rustc_span::Symbol;
 
 pub fn provide(providers: &mut ty::query::Providers) {
     *providers = ty::query::Providers {
@@ -196,20 +197,26 @@ fn associated_types_for_impl_traits_in_associated_fn(
 
     match tcx.def_kind(parent_def_id) {
         DefKind::Trait => {
-            struct RPITVisitor {
-                rpits: Vec<LocalDefId>,
+            struct RPITVisitor<'tcx> {
+                rpits: FxIndexSet<LocalDefId>,
+                tcx: TyCtxt<'tcx>,
             }
 
-            impl<'v> Visitor<'v> for RPITVisitor {
-                fn visit_ty(&mut self, ty: &'v hir::Ty<'v>) {
-                    if let hir::TyKind::OpaqueDef(item_id, _, _) = ty.kind {
-                        self.rpits.push(item_id.owner_id.def_id)
+            impl<'tcx> Visitor<'tcx> for RPITVisitor<'tcx> {
+                fn visit_ty(&mut self, ty: &'tcx hir::Ty<'tcx>) {
+                    if let hir::TyKind::OpaqueDef(item_id, _, _) = ty.kind
+                        && self.rpits.insert(item_id.owner_id.def_id)
+                    {
+                        let opaque_item = self.tcx.hir().expect_item(item_id.owner_id.def_id).expect_opaque_ty();
+                        for bound in opaque_item.bounds {
+                            intravisit::walk_param_bound(self, bound);
+                        }
                     }
                     intravisit::walk_ty(self, ty)
                 }
             }
 
-            let mut visitor = RPITVisitor { rpits: Vec::new() };
+            let mut visitor = RPITVisitor { tcx, rpits: FxIndexSet::default() };
 
             if let Some(output) = tcx.hir().get_fn_output(fn_def_id) {
                 visitor.visit_fn_ret_ty(output);
@@ -227,13 +234,9 @@ fn associated_types_for_impl_traits_in_associated_fn(
 
             tcx.arena.alloc_from_iter(
                 tcx.associated_types_for_impl_traits_in_associated_fn(trait_fn_def_id).iter().map(
-                    move |trait_assoc_def_id| {
-                        associated_type_for_impl_trait_in_impl(
-                            tcx,
-                            trait_assoc_def_id.expect_local(),
-                            fn_def_id,
-                        )
-                        .to_def_id()
+                    move |&trait_assoc_def_id| {
+                        associated_type_for_impl_trait_in_impl(tcx, trait_assoc_def_id, fn_def_id)
+                            .to_def_id()
                     },
                 ),
             )
@@ -254,13 +257,17 @@ fn associated_type_for_impl_trait_in_trait(
     tcx: TyCtxt<'_>,
     opaque_ty_def_id: LocalDefId,
 ) -> LocalDefId {
-    let fn_def_id = tcx.impl_trait_in_trait_parent_fn(opaque_ty_def_id.to_def_id());
-    let trait_def_id = tcx.parent(fn_def_id);
+    let (hir::OpaqueTyOrigin::FnReturn(fn_def_id) | hir::OpaqueTyOrigin::AsyncFn(fn_def_id)) =
+        tcx.hir().expect_item(opaque_ty_def_id).expect_opaque_ty().origin
+    else {
+        bug!("expected opaque for {opaque_ty_def_id:?}");
+    };
+    let trait_def_id = tcx.local_parent(fn_def_id);
     assert_eq!(tcx.def_kind(trait_def_id), DefKind::Trait);
 
     let span = tcx.def_span(opaque_ty_def_id);
-    let trait_assoc_ty =
-        tcx.at(span).create_def(trait_def_id.expect_local(), DefPathData::ImplTraitAssocTy);
+    let name = name_for_impl_trait_in_trait(tcx, opaque_ty_def_id, trait_def_id);
+    let trait_assoc_ty = tcx.at(span).create_def(trait_def_id, DefPathData::ImplTraitAssocTy(name));
 
     let local_def_id = trait_assoc_ty.def_id();
     let def_id = local_def_id.to_def_id();
@@ -275,14 +282,14 @@ fn associated_type_for_impl_trait_in_trait(
     trait_assoc_ty.def_ident_span(Some(span));
 
     trait_assoc_ty.associated_item(ty::AssocItem {
-        name: kw::Empty,
+        name,
         kind: ty::AssocKind::Type,
         def_id,
         trait_item_def_id: None,
         container: ty::TraitContainer,
         fn_has_self_parameter: false,
         opt_rpitit_info: Some(ImplTraitInTraitData::Trait {
-            fn_def_id,
+            fn_def_id: fn_def_id.to_def_id(),
             opaque_def_id: opaque_ty_def_id.to_def_id(),
         }),
     });
@@ -324,7 +331,7 @@ fn associated_type_for_impl_trait_in_trait(
             params.iter().map(|param| (param.def_id, param.index)).collect();
 
         ty::Generics {
-            parent: Some(trait_def_id),
+            parent: Some(trait_def_id.to_def_id()),
             parent_count,
             params,
             param_def_id_to_index,
@@ -335,7 +342,7 @@ fn associated_type_for_impl_trait_in_trait(
 
     // There are no predicates for the synthesized associated type.
     trait_assoc_ty.explicit_predicates_of(ty::GenericPredicates {
-        parent: Some(trait_def_id),
+        parent: Some(trait_def_id.to_def_id()),
         predicates: &[],
     });
 
@@ -345,22 +352,42 @@ fn associated_type_for_impl_trait_in_trait(
     local_def_id
 }
 
+/// Create a stable path name for an associated type for an impl trait in trait
+/// by appending the opaque type's path segments starting from the function name.
+fn name_for_impl_trait_in_trait(
+    tcx: TyCtxt<'_>,
+    opaque_ty_def_id: LocalDefId,
+    trait_def_id: LocalDefId,
+) -> Symbol {
+    let mut name = vec![];
+    let mut def_id = opaque_ty_def_id;
+    while def_id != trait_def_id {
+        name.push(tcx.def_key(def_id.to_def_id()).disambiguated_data.to_string());
+        def_id = tcx.local_parent(def_id);
+    }
+    name.reverse();
+    let name = Symbol::intern(&name.join("::"));
+    name
+}
+
 /// Given an `trait_assoc_def_id` corresponding to an associated item synthesized
 /// from an `impl Trait` in an associated function from a trait, and an
 /// `impl_fn_def_id` that represents an implementation of the associated function
 /// that the `impl Trait` comes from, synthesize an associated type for that `impl Trait`
 /// that inherits properties that we infer from the method and the associated type.
 fn associated_type_for_impl_trait_in_impl(
     tcx: TyCtxt<'_>,
-    trait_assoc_def_id: LocalDefId,
+    trait_assoc_def_id: DefId,
     impl_fn_def_id: LocalDefId,
 ) -> LocalDefId {
     let impl_local_def_id = tcx.local_parent(impl_fn_def_id);
     let impl_def_id = impl_local_def_id.to_def_id();
 
+    let name = tcx.item_name(trait_assoc_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_local_def_id, DefPathData::ImplTraitAssocTy);
+    let impl_assoc_ty =
+        tcx.at(span).create_def(impl_local_def_id, DefPathData::ImplTraitAssocTy(name));
 
     let local_def_id = impl_assoc_ty.def_id();
     let def_id = local_def_id.to_def_id();
@@ -375,10 +402,10 @@ fn associated_type_for_impl_trait_in_impl(
     impl_assoc_ty.def_ident_span(Some(span));
 
     impl_assoc_ty.associated_item(ty::AssocItem {
-        name: kw::Empty,
+        name,
         kind: ty::AssocKind::Type,
         def_id,
-        trait_item_def_id: Some(trait_assoc_def_id.to_def_id()),
+        trait_item_def_id: Some(trait_assoc_def_id),
         container: ty::ImplContainer,
         fn_has_self_parameter: false,
         opt_rpitit_info: Some(ImplTraitInTraitData::Impl { fn_def_id: impl_fn_def_id.to_def_id() }),

tests/ui/impl-trait/in-trait/auxiliary/rpitit.rs

@@ -1,11 +1,14 @@
+// [next] compile-flags: -Zlower-impl-trait-in-trait-to-assoc-ty
+
 #![feature(return_position_impl_trait_in_trait)]
 
+use std::ops::Deref;
+
 pub trait Foo {
-    fn bar() -> impl Sized;
+    fn bar() -> impl Deref<Target = impl Sized>;
 }
 
 pub struct Foreign;
-
 impl Foo for Foreign {
-    fn bar() {}
+    fn bar() -> &'static () { &() }
 }

tests/ui/impl-trait/in-trait/doesnt-satisfy.next.stderr

@@ -6,11 +6,11 @@ LL |     fn bar() -> () {}
    |
    = help: the trait `std::fmt::Display` is not implemented for `()`
    = note: in format strings you may be able to use `{:?}` (or {:#?} for pretty-print) instead
-note: required by a bound in `Foo::{opaque#0}`
+note: required by a bound in `Foo::bar::{opaque#0}`
   --> $DIR/doesnt-satisfy.rs:8:22
    |
 LL |     fn bar() -> impl std::fmt::Display;
-   |                      ^^^^^^^^^^^^^^^^^ required by this bound in `Foo::`
+   |                      ^^^^^^^^^^^^^^^^^ required by this bound in `Foo::bar::{opaque#0}`
 
 error: aborting due to previous error
 

tests/ui/impl-trait/in-trait/foreign.rs

@@ -5,7 +5,17 @@
 
 extern crate rpitit;
 
+use std::sync::Arc;
+
+// Implement an RPITIT from another crate.
+struct Local;
+impl rpitit::Foo for Local {
+    fn bar() -> Arc<String> { Arc::new(String::new()) }
+}
+
 fn main() {
-    // Witness an RPITIT from another crate
-    let () = <rpitit::Foreign as rpitit::Foo>::bar();
+    // Witness an RPITIT from another crate.
+    let &() = <rpitit::Foreign as rpitit::Foo>::bar();
+
+    let x: Arc<String> = <Local as rpitit::Foo>::bar();
 }