intern "substitutions"

chalk-integration/src/lowering.rs

@@ -904,7 +904,7 @@ impl LowerProjectionTy for ProjectionTy {
         } = *self;
         let chalk_ir::TraitRef {
             trait_id,
-            parameters: trait_parameters,
+            substitution: trait_substitution,
         } = trait_ref.lower(env)?;
         let lookup = match env.associated_ty_lookups.get(&(trait_id.into(), name.str)) {
             Some(lookup) => lookup,
@@ -933,11 +933,11 @@ impl LowerProjectionTy for ProjectionTy {
             }
         }
 
-        args.extend(trait_parameters);
+        args.extend(trait_substitution.iter().cloned());
 
         Ok(chalk_ir::ProjectionTy {
             associated_ty_id: lookup.id,
-            parameters: args,
+            substitution: chalk_ir::Substitution::from(args),
         })
     }
 }
@@ -961,7 +961,7 @@ impl LowerTy for Ty {
                     } else {
                         Ok(chalk_ir::TyData::Apply(chalk_ir::ApplicationTy {
                             name: chalk_ir::TypeName::Struct(id),
-                            parameters: vec![],
+                            substitution: chalk_ir::Substitution::empty(),
                         })
                         .intern())
                     }
@@ -1001,10 +1001,8 @@ impl LowerTy for Ty {
                     })?;
                 }
 
-                let parameters = args
-                    .iter()
-                    .map(|t| Ok(t.lower(env)?))
-                    .collect::<LowerResult<Vec<_>>>()?;
+                let substitution =
+                    chalk_ir::Substitution::from_fallible(args.iter().map(|t| Ok(t.lower(env)?)))?;
 
                 for (param, arg) in k.binders.binders.iter().zip(args.iter()) {
                     if param.kind() != arg.kind() {
@@ -1018,7 +1016,7 @@ impl LowerTy for Ty {
 
                 Ok(chalk_ir::TyData::Apply(chalk_ir::ApplicationTy {
                     name: chalk_ir::TypeName::Struct(id),
-                    parameters: parameters,
+                    substitution: substitution,
                 })
                 .intern())
             }

chalk-integration/src/program.rs

@@ -163,8 +163,11 @@ impl RustIrDatabase<ChalkIr> for Program {
             .filter(|(_, impl_datum)| {
                 let trait_ref = &impl_datum.binders.value.trait_ref;
                 trait_id == trait_ref.trait_id && {
-                    assert_eq!(trait_ref.parameters.len(), parameters.len());
-                    <[_] as CouldMatch<[_]>>::could_match(&parameters, &trait_ref.parameters)
+                    assert_eq!(trait_ref.substitution.len(), parameters.len());
+                    <[_] as CouldMatch<[_]>>::could_match(
+                        &parameters,
+                        &trait_ref.substitution.parameters(),
+                    )
                 }
             })
             .map(|(&impl_id, _)| impl_id)
@@ -191,7 +194,7 @@ impl RustIrDatabase<ChalkIr> for Program {
         self.impl_data.values().any(|impl_datum| {
             let impl_trait_ref = &impl_datum.binders.value.trait_ref;
             impl_trait_ref.trait_id == auto_trait_id
-                && match impl_trait_ref.parameters[0].assert_ty_ref().data() {
+                && match impl_trait_ref.self_type_parameter().data() {
                     TyData::Apply(apply) => match apply.name {
                         TypeName::Struct(id) => id == struct_id,
                         _ => false,

chalk-ir/src/cast.rs

@@ -169,6 +169,12 @@ impl<TF: TypeFamily> CastTo<Parameter<TF>> for Lifetime<TF> {
     }
 }
 
+impl<TF: TypeFamily> CastTo<Parameter<TF>> for Parameter<TF> {
+    fn cast_to(self) -> Parameter<TF> {
+        self
+    }
+}
+
 impl<T, TF> CastTo<ProgramClause<TF>> for T
 where
     T: CastTo<DomainGoal<TF>>,

chalk-ir/src/could_match.rs

@@ -24,10 +24,10 @@ where
                         let names_could_match = a.name == b.name;
 
                         names_could_match
-                            && a.parameters
+                            && a.substitution
                                 .iter()
-                                .zip(&b.parameters)
-                                .all(|(p_a, p_b)| p_a.could_match(p_b))
+                                .zip(&b.substitution)
+                                .all(|(p_a, p_b)| p_a.could_match(&p_b))
                     }
 
                     _ => true,

chalk-ir/src/debug.rs

@@ -115,7 +115,8 @@ impl Debug for PlaceholderIndex {
 
 impl<TF: TypeFamily> Debug for ApplicationTy<TF> {
     fn fmt(&self, fmt: &mut Formatter) -> Result<(), Error> {
-        write!(fmt, "{:?}{:?}", self.name, Angle(&self.parameters))
+        let ApplicationTy { name, substitution } = self;
+        write!(fmt, "{:?}{:?}", name, substitution.with_angle())
     }
 }
 
@@ -150,13 +151,14 @@ struct SeparatorTraitRef<'me, TF: TypeFamily> {
 
 impl<TF: TypeFamily> Debug for SeparatorTraitRef<'_, TF> {
     fn fmt(&self, fmt: &mut Formatter) -> Result<(), Error> {
+        let parameters = self.trait_ref.substitution.parameters();
         write!(
             fmt,
             "{:?}{}{:?}{:?}",
-            self.trait_ref.parameters[0],
+            parameters[0],
             self.separator,
             self.trait_ref.trait_id,
-            Angle(&self.trait_ref.parameters[1..])
+            Angle(&parameters[1..])
         )
     }
 }
@@ -168,7 +170,7 @@ impl<TF: TypeFamily> Debug for ProjectionTy<TF> {
                 fmt,
                 "({:?}){:?}",
                 self.associated_ty_id,
-                Angle(&self.parameters)
+                self.substitution.with_angle()
             )
         })
     }
@@ -242,13 +244,9 @@ impl<TF: TypeFamily> Debug for DomainGoal<TF> {
             DomainGoal::IsLocal(n) => write!(fmt, "IsLocal({:?})", n),
             DomainGoal::IsUpstream(n) => write!(fmt, "IsUpstream({:?})", n),
             DomainGoal::IsFullyVisible(n) => write!(fmt, "IsFullyVisible({:?})", n),
-            DomainGoal::LocalImplAllowed(tr) => write!(
-                fmt,
-                "LocalImplAllowed({:?}: {:?}{:?})",
-                tr.parameters[0],
-                tr.trait_id,
-                Angle(&tr.parameters[1..])
-            ),
+            DomainGoal::LocalImplAllowed(tr) => {
+                write!(fmt, "LocalImplAllowed({:?})", tr.with_colon(),)
+            }
             DomainGoal::Compatible(_) => write!(fmt, "Compatible"),
             DomainGoal::DownstreamType(n) => write!(fmt, "DownstreamType({:?})", n),
         }
@@ -413,9 +411,17 @@ impl<TF: TypeFamily> Display for ConstrainedSubst<TF> {
     }
 }
 
+impl<TF: TypeFamily> Substitution<TF> {
+    /// Displays the substitution in the form `< P0, .. Pn >`, or (if
+    /// the substitution is empty) as an empty string.
+    pub fn with_angle(&self) -> Angle<'_, Parameter<TF>> {
+        Angle(self.parameters())
+    }
+}
+
 impl<TF: TypeFamily> Debug for Substitution<TF> {
-    fn fmt(&self, f: &mut Formatter) -> Result<(), Error> {
-        Display::fmt(self, f)
+    fn fmt(&self, fmt: &mut Formatter) -> Result<(), Error> {
+        Display::fmt(self, fmt)
     }
 }
 
@@ -425,7 +431,7 @@ impl<TF: TypeFamily> Display for Substitution<TF> {
 
         write!(f, "[")?;
 
-        for (index, value) in self.parameters.iter().enumerate() {
+        for (index, value) in self.iter().enumerate() {
             if first {
                 first = false;
             } else {

chalk-ir/src/family.rs

@@ -2,6 +2,7 @@ use crate::tls;
 use crate::AssocTypeId;
 use crate::GoalData;
 use crate::LifetimeData;
+use crate::Parameter;
 use crate::ParameterData;
 use crate::ProjectionTy;
 use crate::RawId;
@@ -68,6 +69,14 @@ pub trait TypeFamily: Debug + Copy + Eq + Ord + Hash {
     /// converted back to its underlying data via `goal_data`.
     type InternedGoal: Debug + Clone + Eq + Ord + Hash;
 
+    /// "Interned" representation of a "substitution".  In normal user code,
+    /// `Self::InternedSubstitution` is not referenced. Instead, we refer to
+    /// `Substitution<Self>`, which wraps this type.
+    ///
+    /// An `InternedSubstitution` is created by `intern_substitution` and can be
+    /// converted back to its underlying data via `substitution_data`.
+    type InternedSubstitution: Debug + Clone + Eq + Ord + Hash;
+
     /// The core "id" type used for struct-ids and the like.
     type DefId: Debug + Copy + Eq + Ord + Hash;
 
@@ -147,7 +156,18 @@ pub trait TypeFamily: Debug + Copy + Eq + Ord + Hash {
     fn intern_goal(data: GoalData<Self>) -> Self::InternedGoal;
 
     /// Lookup the `GoalData` that was interned to create a `InternedGoal`.
-    fn goal_data(lifetime: &Self::InternedGoal) -> &GoalData<Self>;
+    fn goal_data(goal: &Self::InternedGoal) -> &GoalData<Self>;
+
+    /// Create an "interned" substitution from `data`. This is not
+    /// normally invoked directly; instead, you invoke
+    /// `SubstitutionData::intern` (which will ultimately call this
+    /// method).
+    fn intern_substitution<E>(
+        data: impl IntoIterator<Item = Result<Parameter<Self>, E>>,
+    ) -> Result<Self::InternedSubstitution, E>;
+
+    /// Lookup the `SubstitutionData` that was interned to create a `InternedSubstitution`.
+    fn substitution_data(substitution: &Self::InternedSubstitution) -> &[Parameter<Self>];
 }
 
 pub trait TargetTypeFamily<TF: TypeFamily>: TypeFamily {
@@ -181,6 +201,7 @@ impl TypeFamily for ChalkIr {
     type InternedLifetime = LifetimeData<ChalkIr>;
     type InternedParameter = ParameterData<ChalkIr>;
     type InternedGoal = Arc<GoalData<ChalkIr>>;
+    type InternedSubstitution = Vec<Parameter<ChalkIr>>;
     type DefId = RawId;
 
     fn debug_struct_id(
@@ -242,6 +263,16 @@ impl TypeFamily for ChalkIr {
     fn goal_data(goal: &Arc<GoalData<ChalkIr>>) -> &GoalData<ChalkIr> {
         goal
     }
+
+    fn intern_substitution<E>(
+        data: impl IntoIterator<Item = Result<Parameter<ChalkIr>, E>>,
+    ) -> Result<Vec<Parameter<ChalkIr>>, E> {
+        data.into_iter().collect()
+    }
+
+    fn substitution_data(substitution: &Vec<Parameter<ChalkIr>>) -> &[Parameter<ChalkIr>] {
+        substitution
+    }
 }
 
 impl HasTypeFamily for ChalkIr {

chalk-ir/src/fold/boring_impls.rs

@@ -86,6 +86,7 @@ impl<T: Fold<TF, TTF>, TF: TypeFamily, TTF: TargetTypeFamily<TF>> Fold<TF, TTF>
         }
     }
 }
+
 impl<TF: TypeFamily, TTF: TargetTypeFamily<TF>> Fold<TF, TTF> for Parameter<TF> {
     type Result = Parameter<TTF>;
     fn fold_with(
@@ -110,6 +111,19 @@ impl<TF: TypeFamily, TTF: TargetTypeFamily<TF>> Fold<TF, TTF> for Goal<TF> {
     }
 }
 
+impl<TF: TypeFamily, TTF: TargetTypeFamily<TF>> Fold<TF, TTF> for Substitution<TF> {
+    type Result = Substitution<TTF>;
+    fn fold_with(
+        &self,
+        folder: &mut dyn Folder<TF, TTF>,
+        binders: usize,
+    ) -> Fallible<Self::Result> {
+        Ok(Substitution::from_fallible(
+            self.iter().map(|p| p.fold_with(folder, binders)),
+        )?)
+    }
+}
+
 #[macro_export]
 macro_rules! copy_fold {
     ($t:ty) => {