Request hidden opaque types lazily

chalk-integration/src/db.rs

@@ -9,7 +9,7 @@ use crate::{
 use chalk_engine::forest::SubstitutionResult;
 use chalk_ir::{
     AdtId, AssocTypeId, Canonical, ConstrainedSubst, Environment, FnDefId, GenericArg, Goal,
-    ImplId, InEnvironment, OpaqueTyId, ProgramClause, ProgramClauses, TraitId, UCanonical,
+    ImplId, InEnvironment, OpaqueTyId, ProgramClause, ProgramClauses, TraitId, Ty, UCanonical,
 };
 use chalk_solve::rust_ir::{
     AdtDatum, AssociatedTyDatum, AssociatedTyValue, AssociatedTyValueId, FnDefDatum, ImplDatum,
@@ -97,6 +97,10 @@ impl RustIrDatabase<ChalkIr> for ChalkDatabase {
         self.program_ir().unwrap().opaque_ty_data(id)
     }
 
+    fn hidden_opaque_type(&self, id: OpaqueTyId<ChalkIr>) -> Ty<ChalkIr> {
+        self.program_ir().unwrap().hidden_opaque_type(id)
+    }
+
     fn adt_datum(&self, id: AdtId<ChalkIr>) -> Arc<AdtDatum<ChalkIr>> {
         self.program_ir().unwrap().adt_datum(id)
     }

chalk-integration/src/lowering.rs

@@ -365,6 +365,7 @@ impl LowerProgram for Program {
         let mut associated_ty_data = BTreeMap::new();
         let mut associated_ty_values = BTreeMap::new();
         let mut opaque_ty_data = BTreeMap::new();
+        let mut hidden_opaque_types = BTreeMap::new();
         let mut custom_clauses = Vec::new();
         for (item, &raw_id) in self.items.iter().zip(&raw_ids) {
             let empty_env = Env {
@@ -500,6 +501,7 @@ impl LowerProgram for Program {
                         // So if we have `type Foo<P1..Pn> = impl Trait<T1..Tn>`, this would introduce `P1..Pn`
                         let binders = empty_env.in_binders(variable_kinds, |env| {
                             let hidden_ty = opaque_ty.ty.lower(&env)?;
+                            hidden_opaque_types.insert(opaque_ty_id, Arc::new(hidden_ty));
 
                             // Introduce a variable to represent the hidden "self type". This will be used in the bounds.
                             // So the `impl Trait<T1..Tn>` will be lowered to `exists<Self> { Self: Trait<T1..Tn> }`.
@@ -530,7 +532,7 @@ impl LowerProgram for Program {
                                     },
                                 )?;
 
-                            Ok(OpaqueTyDatumBound { hidden_ty, bounds })
+                            Ok(OpaqueTyDatumBound { bounds })
                         })?;
 
                         opaque_ty_data.insert(
@@ -562,6 +564,7 @@ impl LowerProgram for Program {
             opaque_ty_ids,
             opaque_ty_kinds,
             opaque_ty_data,
+            hidden_opaque_types,
             custom_clauses,
             object_safe_traits,
         };

chalk-integration/src/program.rs

@@ -56,6 +56,9 @@ pub struct Program {
     /// For each opaque type:
     pub opaque_ty_data: BTreeMap<OpaqueTyId<ChalkIr>, Arc<OpaqueTyDatum<ChalkIr>>>,
 
+    /// Stores the hidden types for opaque types
+    pub hidden_opaque_types: BTreeMap<OpaqueTyId<ChalkIr>, Arc<Ty<ChalkIr>>>,
+
     /// For each trait:
     pub trait_data: BTreeMap<TraitId<ChalkIr>, Arc<TraitDatum<ChalkIr>>>,
 
@@ -336,6 +339,10 @@ impl RustIrDatabase<ChalkIr> for Program {
         self.opaque_ty_data[&id].clone()
     }
 
+    fn hidden_opaque_type(&self, id: OpaqueTyId<ChalkIr>) -> Ty<ChalkIr> {
+        (*self.hidden_opaque_types[&id]).clone()
+    }
+
     fn adt_datum(&self, id: AdtId<ChalkIr>) -> Arc<AdtDatum<ChalkIr>> {
         self.adt_data[&id].clone()
     }

chalk-solve/src/clauses.rs

@@ -142,8 +142,9 @@ pub fn push_auto_trait_impls_opaque<I: Interner>(
         1
     );
 
-    let binders = opaque_ty_datum.bound.map_ref(|b| &b.hidden_ty);
-    builder.push_binders(&binders, |builder, hidden_ty| {
+    let hidden_ty = builder.db.hidden_opaque_type(opaque_id);
+    let binders = opaque_ty_datum.bound.clone();
+    builder.push_binders(&binders, |builder, _| {
         let self_ty: Ty<_> = ApplicationTy {
             name: opaque_id.cast(interner),
             substitution: builder.substitution_in_scope(),

chalk-solve/src/clauses/program_clauses.rs

@@ -151,7 +151,7 @@ impl<I: Interner> ToProgramClauses<I> for OpaqueTyDatum<I> {
                 DomainGoal::Holds(
                     AliasEq {
                         alias: alias.clone(),
-                        ty: opaque_ty_bound.hidden_ty.clone(),
+                        ty: builder.db.hidden_opaque_type(self.opaque_ty_id),
                     }
                     .cast(interner),
                 ),

chalk-solve/src/lib.rs

@@ -51,6 +51,9 @@ pub trait RustIrDatabase<I: Interner>: Debug {
     /// Returns the `OpaqueTyDatum` with the given id.
     fn opaque_ty_data(&self, id: OpaqueTyId<I>) -> Arc<OpaqueTyDatum<I>>;
 
+    /// Returns the "hidden type" corresponding with the opaque type.
+    fn hidden_opaque_type(&self, id: OpaqueTyId<I>) -> Ty<I>;
+
     /// Returns a list of potentially relevant impls for a given
     /// trait-id; we also supply the type parameters that we are
     /// trying to match (if known: these parameters may contain

chalk-solve/src/rust_ir.rs

@@ -544,9 +544,6 @@ pub struct OpaqueTyDatum<I: Interner> {
 
 #[derive(Clone, Debug, PartialEq, Eq, Hash, Fold, HasInterner)]
 pub struct OpaqueTyDatumBound<I: Interner> {
-    /// The value for the "hidden type" for `opaque type Foo = ...`
-    pub hidden_ty: Ty<I>,
-
     /// Trait bounds for the opaque type.
     pub bounds: Binders<Vec<QuantifiedWhereClause<I>>>,
 }

tests/integration/panic.rs

@@ -121,6 +121,10 @@ impl RustIrDatabase<ChalkIr> for MockDatabase {
         unimplemented!()
     }
 
+    fn hidden_opaque_type(&self, id: OpaqueTyId<ChalkIr>) -> Ty<ChalkIr> {
+        unimplemented!()
+    }
+
     fn adt_datum(&self, id: AdtId<ChalkIr>) -> Arc<AdtDatum<ChalkIr>> {
         unimplemented!()
     }