[WIP] Delay def collection for expression-like nodes

compiler/rustc_ast_lowering/src/asm.rs

@@ -7,7 +7,6 @@ use rustc_data_structures::fx::{FxHashMap, FxHashSet, FxIndexMap};
 use rustc_hir as hir;
 use rustc_hir::def::{DefKind, Res};
 use rustc_session::parse::feature_err;
-use rustc_span::symbol::kw;
 use rustc_span::{sym, Span};
 use rustc_target::asm;
 
@@ -222,18 +221,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                             };
 
                             // Wrap the expression in an AnonConst.
-                            let parent_def_id = self.current_def_id_parent;
                             let node_id = self.next_node_id();
-                            // HACK(min_generic_const_args): see lower_anon_const
-                            if !expr.is_potential_trivial_const_arg() {
-                                self.create_def(
-                                    parent_def_id,
-                                    node_id,
-                                    kw::Empty,
-                                    DefKind::AnonConst,
-                                    *op_sp,
-                                );
-                            }
                             let anon_const = AnonConst { id: node_id, value: P(expr) };
                             hir::InlineAsmOperand::SymFn {
                                 anon_const: self.lower_anon_const_to_anon_const(&anon_const),

compiler/rustc_ast_lowering/src/expr.rs

@@ -70,6 +70,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
                 _ => (),
             }
 
+            self.create_def_if_needed_for(e);
             let hir_id = self.lower_node_id(e.id);
             self.lower_attrs(hir_id, &e.attrs);
 
@@ -356,6 +357,54 @@ impl<'hir> LoweringContext<'_, 'hir> {
         })
     }
 
+    /// HACK(min_generic_const_args): we delay creation of expression defs until ast_lowering
+    ///
+    /// This only creates a def for the top-level expression. If it has nested expressions that
+    /// need defs, those are handled by the recursion in the main lowering logic.
+    fn create_def_if_needed_for(&mut self, e: &Expr) {
+        match &e.kind {
+            ExprKind::ConstBlock(c) => {
+                self.create_def(
+                    self.current_def_id_parent,
+                    c.id,
+                    kw::Empty,
+                    DefKind::InlineConst,
+                    c.value.span,
+                );
+            }
+            ExprKind::Closure(box Closure { coroutine_kind, .. }) => {
+                let closure_def = self.create_def(
+                    self.current_def_id_parent,
+                    e.id,
+                    kw::Empty,
+                    DefKind::Closure,
+                    e.span,
+                );
+                if let Some(coroutine_kind) = coroutine_kind {
+                    self.with_def_id_parent(closure_def, |this| {
+                        this.create_def(
+                            this.current_def_id_parent,
+                            coroutine_kind.closure_id(),
+                            kw::Empty,
+                            DefKind::Closure,
+                            e.span,
+                        );
+                    })
+                }
+            }
+            ExprKind::Gen(..) => {
+                self.create_def(
+                    self.current_def_id_parent,
+                    e.id,
+                    kw::Empty,
+                    DefKind::Closure,
+                    e.span,
+                );
+            }
+            _ => {}
+        }
+    }
+
     fn lower_unop(&mut self, u: UnOp) -> hir::UnOp {
         match u {
             UnOp::Deref => hir::UnOp::Deref,
@@ -383,15 +432,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
         let mut generic_args = ThinVec::new();
         for (idx, arg) in args.into_iter().enumerate() {
             if legacy_args_idx.contains(&idx) {
-                let parent_def_id = self.current_def_id_parent;
                 let node_id = self.next_node_id();
-
-                // HACK(min_generic_const_args): see lower_anon_const
-                if !arg.is_potential_trivial_const_arg() {
-                    // Add a definition for the in-band const def.
-                    self.create_def(parent_def_id, node_id, kw::Empty, DefKind::AnonConst, f.span);
-                }
-
                 let anon_const = AnonConst { id: node_id, value: arg };
                 generic_args.push(AngleBracketedArg::Arg(GenericArg::Const(anon_const)));
             } else {

compiler/rustc_ast_lowering/src/index.rs

@@ -146,6 +146,10 @@ impl<'a, 'hir> Visitor<'hir> for NodeCollector<'a, 'hir> {
         self.visit_body(body);
     }
 
+    fn visit_nested_opaque_ty(&mut self, opaq: &'hir OpaqueTy<'hir>) -> Self::Result {
+        self.visit_opaque_ty(opaq)
+    }
+
     fn visit_param(&mut self, param: &'hir Param<'hir>) {
         let node = Node::Param(param);
         self.insert(param.pat.span, param.hir_id, node);
@@ -228,6 +232,14 @@ impl<'a, 'hir> Visitor<'hir> for NodeCollector<'a, 'hir> {
         });
     }
 
+    fn visit_opaque_ty(&mut self, opaq: &'hir OpaqueTy<'hir>) {
+        self.insert(opaq.span, opaq.hir_id, Node::OpaqueTy(opaq));
+
+        self.with_parent(opaq.hir_id, |this| {
+            intravisit::walk_opaque_ty(this, opaq);
+        });
+    }
+
     fn visit_anon_const(&mut self, constant: &'hir AnonConst) {
         // FIXME: use real span?
         self.insert(DUMMY_SP, constant.hir_id, Node::AnonConst(constant));

compiler/rustc_ast_lowering/src/item.rs

@@ -1160,6 +1160,13 @@ impl<'hir> LoweringContext<'_, 'hir> {
         let (Some(coroutine_kind), Some(body)) = (coroutine_kind, body) else {
             return self.lower_fn_body_block(span, decl, body);
         };
+        self.create_def(
+            self.current_def_id_parent,
+            coroutine_kind.closure_id(),
+            kw::Empty,
+            DefKind::Closure,
+            span,
+        );
         self.lower_body(|this| {
             let (parameters, expr) = this.lower_coroutine_body_with_moved_arguments(
                 decl,

compiler/rustc_ast_lowering/src/lib.rs

@@ -828,7 +828,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
             LifetimeRes::Fresh { param, kind, .. } => {
                 // Late resolution delegates to us the creation of the `LocalDefId`.
                 let _def_id = self.create_def(
-                    self.current_hir_id_owner.def_id, // FIXME: should this use self.current_def_id_parent?
+                    self.current_def_id_parent,
                     param,
                     kw::UnderscoreLifetime,
                     DefKind::LifetimeParam,
@@ -1412,7 +1412,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                         );
 
                         self.create_def(
-                            self.current_hir_id_owner.def_id, // FIXME: should this use self.current_def_id_parent?
+                            self.current_def_id_parent,
                             *def_node_id,
                             ident.name,
                             DefKind::TyParam,
@@ -1619,14 +1619,16 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
         opaque_ty_span: Span,
         lower_item_bounds: impl FnOnce(&mut Self) -> &'hir [hir::GenericBound<'hir>],
     ) -> hir::TyKind<'hir> {
+        let opaque_ty_hir_id = self.next_id();
         let opaque_ty_def_id = self.create_def(
-            self.current_hir_id_owner.def_id, // FIXME: should this use self.current_def_id_parent?
+            self.current_def_id_parent,
             opaque_ty_node_id,
             kw::Empty,
             DefKind::OpaqueTy,
             opaque_ty_span,
         );
         debug!(?opaque_ty_def_id);
+        self.children.push((opaque_ty_def_id, hir::MaybeOwner::NonOwner(opaque_ty_hir_id)));
 
         // Map from captured (old) lifetime to synthetic (new) lifetime.
         // Used to resolve lifetimes in the bounds of the opaque.
@@ -1699,7 +1701,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
             }
         }
 
-        self.with_hir_id_owner(opaque_ty_node_id, |this| {
+        let opaque_ty_def = self.with_def_id_parent(opaque_ty_def_id, |this| {
             // Install the remapping from old to new (if any). This makes sure that
             // any lifetimes that would have resolved to the def-id of captured
             // lifetimes are remapped to the new *synthetic* lifetimes of the opaque.
@@ -1737,7 +1739,10 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
 
             let lifetime_mapping = self.arena.alloc_slice(&synthesized_lifetime_args);
 
-            let opaque_ty_item = hir::OpaqueTy {
+            trace!("registering opaque type with id {:#?}", opaque_ty_def_id);
+            let opaque_ty_def = hir::OpaqueTy {
+                hir_id: opaque_ty_hir_id,
+                def_id: opaque_ty_def_id,
                 generics: this.arena.alloc(hir::Generics {
                     params: generic_params,
                     predicates: &[],
@@ -1749,19 +1754,9 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
                 origin,
                 lifetime_mapping,
                 in_trait,
-            };
-
-            // Generate an `type Foo = impl Trait;` declaration.
-            trace!("registering opaque type with id {:#?}", opaque_ty_def_id);
-            let opaque_ty_item = hir::Item {
-                owner_id: hir::OwnerId { def_id: opaque_ty_def_id },
-                ident: Ident::empty(),
-                kind: hir::ItemKind::OpaqueTy(this.arena.alloc(opaque_ty_item)),
-                vis_span: this.lower_span(span.shrink_to_lo()),
                 span: this.lower_span(opaque_ty_span),
             };
-
-            hir::OwnerNode::Item(this.arena.alloc(opaque_ty_item))
+            this.arena.alloc(opaque_ty_def)
         });
 
         let generic_args = self.arena.alloc_from_iter(
@@ -1774,11 +1769,7 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
         // Foo = impl Trait` is, internally, created as a child of the
         // async fn, so the *type parameters* are inherited. It's
         // only the lifetime parameters that we must supply.
-        hir::TyKind::OpaqueDef(
-            hir::ItemId { owner_id: hir::OwnerId { def_id: opaque_ty_def_id } },
-            generic_args,
-            in_trait,
-        )
+        hir::TyKind::OpaqueDef(opaque_ty_def, generic_args, in_trait)
     }
 
     fn lower_precise_capturing_args(
@@ -2465,19 +2456,16 @@ impl<'a, 'hir> LoweringContext<'a, 'hir> {
     /// See [`hir::ConstArg`] for when to use this function vs
     /// [`Self::lower_anon_const_to_const_arg`].
     fn lower_anon_const_to_anon_const(&mut self, c: &AnonConst) -> &'hir hir::AnonConst {
-        if c.value.is_potential_trivial_const_arg() {
-            // HACK(min_generic_const_args): see DefCollector::visit_anon_const
-            // Over there, we guess if this is a bare param and only create a def if
-            // we think it's not. However we may can guess wrong (see there for example)
-            // in which case we have to create the def here.
-            self.create_def(
-                self.current_def_id_parent,
-                c.id,
-                kw::Empty,
-                DefKind::AnonConst,
-                c.value.span,
-            );
-        }
+        // HACK(min_generic_const_args): see DefCollector::visit_anon_const
+        // We delay creation of defs for expression-like things, including anon consts.
+        // This is because some anon consts end up as `ConstArgKind::Path`'s instead.
+        self.create_def(
+            self.current_def_id_parent,
+            c.id,
+            kw::Empty,
+            DefKind::AnonConst,
+            c.value.span,
+        );
 
         self.arena.alloc(self.with_new_scopes(c.value.span, |this| {
             let def_id = this.local_def_id(c.id);

compiler/rustc_borrowck/src/diagnostics/region_name.rs

@@ -829,20 +829,14 @@ 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 = self.infcx.tcx.hir();
-
-        let hir::TyKind::OpaqueDef(id, _, _) = 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: {:?}",
                 hir_ty
             );
         };
-        let opaque_ty = hir.item(id);
-        if let hir::ItemKind::OpaqueTy(hir::OpaqueTy {
-            bounds: [hir::GenericBound::Trait(trait_ref, _)],
-            ..
-        }) = opaque_ty.kind
+        if let hir::OpaqueTy { bounds: [hir::GenericBound::Trait(trait_ref, _)], .. } = opaque_ty
             && let Some(segment) = trait_ref.trait_ref.path.segments.last()
             && let Some(args) = segment.args
             && let [constraint] = args.constraints

compiler/rustc_borrowck/src/region_infer/opaque_types.rs

@@ -328,8 +328,8 @@ fn check_opaque_type_well_formed<'tcx>(
 ) -> Result<Ty<'tcx>, ErrorGuaranteed> {
     // Only check this for TAIT. RPIT already supports `tests/ui/impl-trait/nested-return-type2.rs`
     // on stable and we'd break that.
-    let opaque_ty_hir = tcx.hir().expect_item(def_id);
-    let OpaqueTyOrigin::TyAlias { .. } = opaque_ty_hir.expect_opaque_ty().origin else {
+    let opaque_ty_hir = tcx.hir().expect_opaque_ty(def_id);
+    let OpaqueTyOrigin::TyAlias { .. } = opaque_ty_hir.origin else {
         return Ok(definition_ty);
     };
     let param_env = tcx.param_env(def_id);

compiler/rustc_hir/src/hir.rs

@@ -2727,6 +2727,8 @@ pub struct BareFnTy<'hir> {
 
 #[derive(Debug, Clone, Copy, HashStable_Generic)]
 pub struct OpaqueTy<'hir> {
+    pub hir_id: HirId,
+    pub def_id: LocalDefId,
     pub generics: &'hir Generics<'hir>,
     pub bounds: GenericBounds<'hir>,
     pub origin: OpaqueTyOrigin,
@@ -2744,6 +2746,7 @@ pub struct OpaqueTy<'hir> {
     /// originating from a trait method. This makes it so that the opaque is
     /// lowered as an associated type.
     pub in_trait: bool,
+    pub span: Span,
 }
 
 #[derive(Debug, Clone, Copy, HashStable_Generic)]
@@ -2835,7 +2838,7 @@ pub enum TyKind<'hir> {
     /// possibly parameters) that are actually bound on the `impl Trait`.
     ///
     /// The last parameter specifies whether this opaque appears in a trait definition.
-    OpaqueDef(ItemId, &'hir [GenericArg<'hir>], bool),
+    OpaqueDef(&'hir OpaqueTy<'hir>, &'hir [GenericArg<'hir>], bool),
     /// A trait object type `Bound1 + Bound2 + Bound3`
     /// where `Bound` is a trait or a lifetime.
     TraitObject(
@@ -3302,8 +3305,6 @@ impl<'hir> Item<'hir> {
         expect_ty_alias, (&'hir Ty<'hir>, &'hir Generics<'hir>),
             ItemKind::TyAlias(ty, generics), (ty, generics);
 
-        expect_opaque_ty, &OpaqueTy<'hir>, ItemKind::OpaqueTy(ty), ty;
-
         expect_enum, (&EnumDef<'hir>, &'hir Generics<'hir>), ItemKind::Enum(def, generics), (def, generics);
 
         expect_struct, (&VariantData<'hir>, &'hir Generics<'hir>),
@@ -3416,8 +3417,6 @@ pub enum ItemKind<'hir> {
     GlobalAsm(&'hir InlineAsm<'hir>),
     /// A type alias, e.g., `type Foo = Bar<u8>`.
     TyAlias(&'hir Ty<'hir>, &'hir Generics<'hir>),
-    /// An opaque `impl Trait` type alias, e.g., `type Foo = impl Bar;`.
-    OpaqueTy(&'hir OpaqueTy<'hir>),
     /// An enum definition, e.g., `enum Foo<A, B> {C<A>, D<B>}`.
     Enum(EnumDef<'hir>, &'hir Generics<'hir>),
     /// A struct definition, e.g., `struct Foo<A> {x: A}`.
@@ -3461,7 +3460,6 @@ impl ItemKind<'_> {
             ItemKind::Fn(_, ref generics, _)
             | ItemKind::TyAlias(_, ref generics)
             | ItemKind::Const(_, ref generics, _)
-            | ItemKind::OpaqueTy(OpaqueTy { ref generics, .. })
             | ItemKind::Enum(_, ref generics)
             | ItemKind::Struct(_, ref generics)
             | ItemKind::Union(_, ref generics)
@@ -3484,7 +3482,6 @@ impl ItemKind<'_> {
             ItemKind::ForeignMod { .. } => "extern block",
             ItemKind::GlobalAsm(..) => "global asm item",
             ItemKind::TyAlias(..) => "type alias",
-            ItemKind::OpaqueTy(..) => "opaque type",
             ItemKind::Enum(..) => "enum",
             ItemKind::Struct(..) => "struct",
             ItemKind::Union(..) => "union",
@@ -3769,6 +3766,7 @@ pub enum Node<'hir> {
     Ty(&'hir Ty<'hir>),
     AssocItemConstraint(&'hir AssocItemConstraint<'hir>),
     TraitRef(&'hir TraitRef<'hir>),
+    OpaqueTy(&'hir OpaqueTy<'hir>),
     Pat(&'hir Pat<'hir>),
     PatField(&'hir PatField<'hir>),
     Arm(&'hir Arm<'hir>),
@@ -3834,6 +3832,7 @@ impl<'hir> Node<'hir> {
             | Node::Crate(..)
             | Node::Ty(..)
             | Node::TraitRef(..)
+            | Node::OpaqueTy(..)
             | Node::Infer(..)
             | Node::WhereBoundPredicate(..)
             | Node::ArrayLenInfer(..)
@@ -3954,6 +3953,7 @@ impl<'hir> Node<'hir> {
             | Node::TraitItem(TraitItem { generics, .. })
             | Node::ImplItem(ImplItem { generics, .. }) => Some(generics),
             Node::Item(item) => item.kind.generics(),
+            Node::OpaqueTy(opaq) => Some(opaq.generics),
             _ => None,
         }
     }
@@ -4013,6 +4013,7 @@ impl<'hir> Node<'hir> {
         expect_ty,            &'hir Ty<'hir>,           Node::Ty(n),           n;
         expect_assoc_item_constraint,  &'hir AssocItemConstraint<'hir>,  Node::AssocItemConstraint(n),  n;
         expect_trait_ref,     &'hir TraitRef<'hir>,     Node::TraitRef(n),     n;
+        expect_opaque_ty,     &'hir OpaqueTy<'hir>,     Node::OpaqueTy(n),     n;
         expect_pat,           &'hir Pat<'hir>,          Node::Pat(n),          n;
         expect_pat_field,     &'hir PatField<'hir>,     Node::PatField(n),     n;
         expect_arm,           &'hir Arm<'hir>,          Node::Arm(n),          n;