4 files changed, 27 insertions, 30 deletions

diff --git a/crates/hir_ty/src/infer/coerce.rs b/crates/hir_ty/src/infer/coerce.rs
index b86474ed4..07eb96573 100644
--- a/crates/hir_ty/src/infer/coerce.rs
+++ b/crates/hir_ty/src/infer/coerce.rs
@@ -4,12 +4,11 @@
 //!
 //! See: https://doc.rust-lang.org/nomicon/coercions.html
 
-use chalk_ir::{Mutability, TyVariableKind};
+use chalk_ir::{cast::Cast, Mutability, TyVariableKind};
 use hir_def::lang_item::LangItemTarget;
 
 use crate::{
-    autoderef, to_chalk_trait_id, traits::Solution, Interner, Obligation, Substitution, TraitRef,
-    Ty, TyKind,
+    autoderef, to_chalk_trait_id, traits::Solution, Interner, Substitution, TraitRef, Ty, TyKind,
 };
 
 use super::{InEnvironment, InferenceContext};
@@ -143,7 +142,7 @@ impl<'a> InferenceContext<'a> {
             .build();
         let trait_ref =
             TraitRef { trait_id: to_chalk_trait_id(coerce_unsized_trait), substitution: substs };
-        let goal = InEnvironment::new(self.trait_env.clone(), Obligation::Trait(trait_ref));
+        let goal = InEnvironment::new(self.trait_env.clone(), trait_ref.cast(&Interner));
 
         let canonicalizer = self.canonicalizer();
         let canonicalized = canonicalizer.canonicalize_obligation(goal);
diff --git a/crates/hir_ty/src/infer/expr.rs b/crates/hir_ty/src/infer/expr.rs
index 93548b6c0..79bbc5dab 100644
--- a/crates/hir_ty/src/infer/expr.rs
+++ b/crates/hir_ty/src/infer/expr.rs
@@ -3,7 +3,7 @@
 use std::iter::{repeat, repeat_with};
 use std::{mem, sync::Arc};
 
-use chalk_ir::{Mutability, TyVariableKind};
+use chalk_ir::{cast::Cast, Mutability, TyVariableKind};
 use hir_def::{
     expr::{Array, BinaryOp, Expr, ExprId, Literal, Statement, UnaryOp},
     path::{GenericArg, GenericArgs},
@@ -21,7 +21,7 @@ use crate::{
     to_assoc_type_id, to_chalk_trait_id,
     traits::{chalk::from_chalk, FnTrait, InEnvironment},
     utils::{generics, variant_data, Generics},
-    AdtId, Binders, CallableDefId, FnPointer, FnSig, Interner, Obligation, Rawness, Scalar,
+    AdtId, Binders, CallableDefId, DomainGoal, FnPointer, FnSig, Interner, Rawness, Scalar,
     Substitution, TraitRef, Ty, TyKind,
 };
 
@@ -90,10 +90,9 @@ impl<'a> InferenceContext<'a> {
             Substitution::build_for_generics(&generic_params).push(ty.clone()).push(arg_ty).build();
 
         let trait_env = Arc::clone(&self.trait_env);
-        let implements_fn_trait = Obligation::Trait(TraitRef {
-            trait_id: to_chalk_trait_id(fn_once_trait),
-            substitution: substs.clone(),
-        });
+        let implements_fn_trait: DomainGoal =
+            TraitRef { trait_id: to_chalk_trait_id(fn_once_trait), substitution: substs.clone() }
+                .cast(&Interner);
         let goal = self.canonicalizer().canonicalize_obligation(InEnvironment {
             value: implements_fn_trait.clone(),
             environment: trait_env,
@@ -938,22 +937,20 @@ impl<'a> InferenceContext<'a> {
             let generic_predicates = self.db.generic_predicates(def.into());
             for predicate in generic_predicates.iter() {
                 let predicate = predicate.clone().subst(parameters);
-                if let Some(obligation) = Obligation::from_predicate(predicate) {
-                    self.obligations.push(obligation);
-                }
+                self.obligations.push(predicate.cast(&Interner));
             }
             // add obligation for trait implementation, if this is a trait method
             match def {
                 CallableDefId::FunctionId(f) => {
                     if let AssocContainerId::TraitId(trait_) = f.lookup(self.db.upcast()).container
                     {
-                        // construct a TraitDef
+                        // construct a TraitRef
                         let substs =
                             parameters.prefix(generics(self.db.upcast(), trait_.into()).len());
-                        self.obligations.push(Obligation::Trait(TraitRef {
-                            trait_id: to_chalk_trait_id(trait_),
-                            substitution: substs,
-                        }));
+                        self.obligations.push(
+                            TraitRef { trait_id: to_chalk_trait_id(trait_), substitution: substs }
+                                .cast(&Interner),
+                        );
                     }
                 }
                 CallableDefId::StructId(_) | CallableDefId::EnumVariantId(_) => {}
diff --git a/crates/hir_ty/src/infer/path.rs b/crates/hir_ty/src/infer/path.rs
index e15135fc1..58cce56ab 100644
--- a/crates/hir_ty/src/infer/path.rs
+++ b/crates/hir_ty/src/infer/path.rs
@@ -2,6 +2,7 @@
 
 use std::iter;
 
+use chalk_ir::cast::Cast;
 use hir_def::{
     path::{Path, PathSegment},
     resolver::{ResolveValueResult, Resolver, TypeNs, ValueNs},
@@ -256,10 +257,13 @@ impl<'a> InferenceContext<'a> {
                             .push(ty.clone())
                             .fill(std::iter::repeat_with(|| self.table.new_type_var()))
                             .build();
-                        self.obligations.push(super::Obligation::Trait(TraitRef {
-                            trait_id: to_chalk_trait_id(trait_),
-                            substitution: trait_substs.clone(),
-                        }));
+                        self.obligations.push(
+                            TraitRef {
+                                trait_id: to_chalk_trait_id(trait_),
+                                substitution: trait_substs.clone(),
+                            }
+                            .cast(&Interner),
+                        );
                         Some(trait_substs)
                     }
                     AssocContainerId::ModuleId(_) => None,
diff --git a/crates/hir_ty/src/infer/unify.rs b/crates/hir_ty/src/infer/unify.rs
index 5b7b423fa..1fc03c8f4 100644
--- a/crates/hir_ty/src/infer/unify.rs
+++ b/crates/hir_ty/src/infer/unify.rs
@@ -5,7 +5,7 @@ use std::borrow::Cow;
 use chalk_ir::{FloatTy, IntTy, TyVariableKind};
 use ena::unify::{InPlaceUnificationTable, NoError, UnifyKey, UnifyValue};
 
-use super::{InferenceContext, Obligation};
+use super::{DomainGoal, InferenceContext};
 use crate::{
     AliasEq, AliasTy, BoundVar, Canonical, DebruijnIndex, FnPointer, InEnvironment, InferenceVar,
     Interner, Scalar, Substitution, Ty, TyKind, TypeWalk, WhereClause,
@@ -87,14 +87,11 @@ impl<'a, 'b> Canonicalizer<'a, 'b> {
 
     pub(crate) fn canonicalize_obligation(
         mut self,
-        obligation: InEnvironment<Obligation>,
-    ) -> Canonicalized<InEnvironment<Obligation>> {
+        obligation: InEnvironment<DomainGoal>,
+    ) -> Canonicalized<InEnvironment<DomainGoal>> {
         let result = match obligation.value {
-            Obligation::Trait(tr) => {
-                Obligation::Trait(self.do_canonicalize(tr, DebruijnIndex::INNERMOST))
-            }
-            Obligation::AliasEq(alias_eq) => {
-                Obligation::AliasEq(self.do_canonicalize(alias_eq, DebruijnIndex::INNERMOST))
+            DomainGoal::Holds(wc) => {
+                DomainGoal::Holds(self.do_canonicalize(wc, DebruijnIndex::INNERMOST))
             }
         };
         self.into_canonicalized(InEnvironment {