7 files changed, 53 insertions, 33 deletions

diff --git a/crates/hir/src/lib.rs b/crates/hir/src/lib.rs
index 8d00f7401..caa22dace 100644
--- a/crates/hir/src/lib.rs
+++ b/crates/hir/src/lib.rs
@@ -58,9 +58,8 @@ use hir_ty::{
     subst_prefix,
     traits::FnTrait,
     AliasEq, AliasTy, BoundVar, CallableDefId, CallableSig, Canonical, CanonicalVarKinds, Cast,
-    DebruijnIndex, InEnvironment, Interner, QuantifiedWhereClause, Scalar, Solution,
-    SolutionVariables, Substitution, TraitEnvironment, Ty, TyBuilder, TyDefId, TyExt, TyKind,
-    TyVariableKind, WhereClause,
+    DebruijnIndex, InEnvironment, Interner, QuantifiedWhereClause, Scalar, Solution, Substitution,
+    TraitEnvironment, Ty, TyBuilder, TyDefId, TyExt, TyKind, TyVariableKind, WhereClause,
 };
 use itertools::Itertools;
 use rustc_hash::FxHashSet;
@@ -1822,8 +1821,9 @@ impl Type {
         );
 
         match db.trait_solve(self.krate, goal)? {
-            Solution::Unique(SolutionVariables(subst)) => subst
+            Solution::Unique(s) => s
                 .value
+                .subst
                 .interned()
                 .first()
                 .map(|ty| self.derived(ty.assert_ty_ref(&Interner).clone())),
diff --git a/crates/hir_ty/src/autoderef.rs b/crates/hir_ty/src/autoderef.rs
index c5890e24d..80e192a57 100644
--- a/crates/hir_ty/src/autoderef.rs
+++ b/crates/hir_ty/src/autoderef.rs
@@ -120,8 +120,8 @@ fn deref_by_trait(
             // assumptions will be broken. We would need to properly introduce
             // new variables in that case
 
-            for i in 1..vars.0.binders.len(&Interner) {
-                if vars.0.value.at(&Interner, i - 1).assert_ty_ref(&Interner).kind(&Interner)
+            for i in 1..vars.binders.len(&Interner) {
+                if vars.value.subst.at(&Interner, i - 1).assert_ty_ref(&Interner).kind(&Interner)
                     != &TyKind::BoundVar(BoundVar::new(DebruijnIndex::INNERMOST, i - 1))
                 {
                     warn!("complex solution for derefing {:?}: {:?}, ignoring", ty.goal, solution);
@@ -130,12 +130,12 @@ fn deref_by_trait(
             }
             Some(Canonical {
                 value: vars
-                    .0
                     .value
-                    .at(&Interner, vars.0.value.len(&Interner) - 1)
+                    .subst
+                    .at(&Interner, vars.value.subst.len(&Interner) - 1)
                     .assert_ty_ref(&Interner)
                     .clone(),
-                binders: vars.0.binders.clone(),
+                binders: vars.binders.clone(),
             })
         }
         Solution::Ambig(_) => {
diff --git a/crates/hir_ty/src/infer.rs b/crates/hir_ty/src/infer.rs
index 75d633c96..7c6c3600b 100644
--- a/crates/hir_ty/src/infer.rs
+++ b/crates/hir_ty/src/infer.rs
@@ -42,7 +42,7 @@ use super::{
 };
 use crate::{
     db::HirDatabase, infer::diagnostics::InferenceDiagnostic, lower::ImplTraitLoweringMode,
-    to_assoc_type_id, AliasEq, AliasTy, Interner, TyBuilder, TyExt, TyKind,
+    to_assoc_type_id, AliasEq, AliasTy, Canonical, Interner, TyBuilder, TyExt, TyKind,
 };
 
 // This lint has a false positive here. See the link below for details.
@@ -342,11 +342,18 @@ impl<'a> InferenceContext<'a> {
                 self.db.trait_solve(self.resolver.krate().unwrap(), canonicalized.value.clone());
 
             match solution {
-                Some(Solution::Unique(substs)) => {
-                    canonicalized.apply_solution(self, substs.0);
+                Some(Solution::Unique(canonical_subst)) => {
+                    canonicalized.apply_solution(
+                        self,
+                        Canonical {
+                            binders: canonical_subst.binders,
+                            // FIXME: handle constraints
+                            value: canonical_subst.value.subst,
+                        },
+                    );
                 }
                 Some(Solution::Ambig(Guidance::Definite(substs))) => {
-                    canonicalized.apply_solution(self, substs.0);
+                    canonicalized.apply_solution(self, substs);
                     self.obligations.push(obligation);
                 }
                 Some(_) => {
diff --git a/crates/hir_ty/src/infer/coerce.rs b/crates/hir_ty/src/infer/coerce.rs
index 159a53a63..f1af2a0bd 100644
--- a/crates/hir_ty/src/infer/coerce.rs
+++ b/crates/hir_ty/src/infer/coerce.rs
@@ -7,7 +7,7 @@
 use chalk_ir::{cast::Cast, Mutability, TyVariableKind};
 use hir_def::lang_item::LangItemTarget;
 
-use crate::{autoderef, Interner, Solution, Ty, TyBuilder, TyExt, TyKind};
+use crate::{autoderef, Canonical, Interner, Solution, Ty, TyBuilder, TyExt, TyKind};
 
 use super::{InEnvironment, InferenceContext};
 
@@ -148,7 +148,14 @@ impl<'a> InferenceContext<'a> {
 
         match solution {
             Solution::Unique(v) => {
-                canonicalized.apply_solution(self, v.0);
+                canonicalized.apply_solution(
+                    self,
+                    Canonical {
+                        binders: v.binders,
+                        // FIXME handle constraints
+                        value: v.value.subst,
+                    },
+                );
             }
             _ => return None,
         };
diff --git a/crates/hir_ty/src/traits.rs b/crates/hir_ty/src/traits.rs
index c8883485c..3374532c3 100644
--- a/crates/hir_ty/src/traits.rs
+++ b/crates/hir_ty/src/traits.rs
@@ -9,7 +9,7 @@ use stdx::panic_context;
 
 use crate::{
     db::HirDatabase, AliasEq, AliasTy, Canonical, DomainGoal, Guidance, HirDisplay, InEnvironment,
-    Solution, SolutionVariables, Ty, TyKind, WhereClause,
+    Solution, Ty, TyKind, WhereClause,
 };
 
 use self::chalk::{from_chalk, Interner, ToChalk};
@@ -173,23 +173,15 @@ fn solution_from_chalk(
     db: &dyn HirDatabase,
     solution: chalk_solve::Solution<Interner>,
 ) -> Solution {
-    let convert_subst = |subst: chalk_ir::Canonical<chalk_ir::Substitution<Interner>>| {
-        let result = from_chalk(db, subst);
-        SolutionVariables(result)
-    };
     match solution {
         chalk_solve::Solution::Unique(constr_subst) => {
-            let subst = chalk_ir::Canonical {
-                value: constr_subst.value.subst,
-                binders: constr_subst.binders,
-            };
-            Solution::Unique(convert_subst(subst))
+            Solution::Unique(from_chalk(db, constr_subst))
         }
         chalk_solve::Solution::Ambig(chalk_solve::Guidance::Definite(subst)) => {
-            Solution::Ambig(Guidance::Definite(convert_subst(subst)))
+            Solution::Ambig(Guidance::Definite(from_chalk(db, subst)))
         }
         chalk_solve::Solution::Ambig(chalk_solve::Guidance::Suggested(subst)) => {
-            Solution::Ambig(Guidance::Suggested(convert_subst(subst)))
+            Solution::Ambig(Guidance::Suggested(from_chalk(db, subst)))
         }
         chalk_solve::Solution::Ambig(chalk_solve::Guidance::Unknown) => {
             Solution::Ambig(Guidance::Unknown)
diff --git a/crates/hir_ty/src/traits/chalk/mapping.rs b/crates/hir_ty/src/traits/chalk/mapping.rs
index 0536b934e..84abd99b2 100644
--- a/crates/hir_ty/src/traits/chalk/mapping.rs
+++ b/crates/hir_ty/src/traits/chalk/mapping.rs
@@ -11,8 +11,8 @@ use hir_def::{GenericDefId, TypeAliasId};
 
 use crate::{
     chalk_ext::ProjectionTyExt, db::HirDatabase, static_lifetime, AliasTy, CallableDefId,
-    Canonical, DomainGoal, FnPointer, GenericArg, InEnvironment, OpaqueTy, ProjectionTy,
-    QuantifiedWhereClause, Substitution, TraitRef, Ty, TypeWalk, WhereClause,
+    Canonical, ConstrainedSubst, DomainGoal, FnPointer, GenericArg, InEnvironment, OpaqueTy,
+    ProjectionTy, QuantifiedWhereClause, Substitution, TraitRef, Ty, TypeWalk, WhereClause,
 };
 
 use super::interner::*;
@@ -459,6 +459,18 @@ where
     }
 }
 
+impl ToChalk for crate::ConstrainedSubst {
+    type Chalk = chalk_ir::ConstrainedSubst<Interner>;
+
+    fn to_chalk(self, _db: &dyn HirDatabase) -> Self::Chalk {
+        unimplemented!()
+    }
+
+    fn from_chalk(db: &dyn HirDatabase, chalk: Self::Chalk) -> Self {
+        ConstrainedSubst { subst: from_chalk(db, chalk.subst) }
+    }
+}
+
 pub(super) fn make_binders<T>(value: T, num_vars: usize) -> chalk_ir::Binders<T>
 where
     T: HasInterner<Interner = Interner>,
diff --git a/crates/hir_ty/src/types.rs b/crates/hir_ty/src/types.rs
index eac1b7900..c25bc2d6a 100644
--- a/crates/hir_ty/src/types.rs
+++ b/crates/hir_ty/src/types.rs
@@ -490,14 +490,16 @@ pub struct AliasEq {
 }
 
 #[derive(Clone, Debug, PartialEq, Eq)]
-pub struct SolutionVariables(pub Canonical<Substitution>);
+pub struct ConstrainedSubst {
+    pub subst: Substitution,
+}
 
 #[derive(Clone, Debug, PartialEq, Eq)]
 /// A (possible) solution for a proposed goal.
 pub enum Solution {
     /// The goal indeed holds, and there is a unique value for all existential
     /// variables.
-    Unique(SolutionVariables),
+    Unique(Canonical<ConstrainedSubst>),
 
     /// The goal may be provable in multiple ways, but regardless we may have some guidance
     /// for type inference. In this case, we don't return any lifetime
@@ -513,12 +515,12 @@ pub enum Guidance {
     /// The existential variables *must* have the given values if the goal is
     /// ever to hold, but that alone isn't enough to guarantee the goal will
     /// actually hold.
-    Definite(SolutionVariables),
+    Definite(Canonical<Substitution>),
 
     /// There are multiple plausible values for the existentials, but the ones
     /// here are suggested as the preferred choice heuristically. These should
     /// be used for inference fallback only.
-    Suggested(SolutionVariables),
+    Suggested(Canonical<Substitution>),
 
     /// There's no useful information to feed back to type inference
     Unknown,