Fix more chalk lowering issues

- Implement lowering for subtype goals
- Use correct lang item for Generator trait
- Use `lower_into` for lowering `ty::Variance`

Author: matthewjasper

compiler/rustc_traits/src/chalk/db.rs

@@ -546,11 +546,11 @@ impl<'tcx> chalk_solve::RustIrDatabase<RustInterner<'tcx>> for RustIrDatabase<'t
             Fn => lang_items.fn_trait(),
             FnMut => lang_items.fn_mut_trait(),
             FnOnce => lang_items.fn_once_trait(),
+            Generator => lang_items.gen_trait(),
             Unsize => lang_items.unsize_trait(),
             Unpin => lang_items.unpin_trait(),
             CoerceUnsized => lang_items.coerce_unsized_trait(),
             DiscriminantKind => lang_items.discriminant_kind_trait(),
-            Generator => lang_items.generator_return(),
         };
         def_id.map(chalk_ir::TraitId)
     }
@@ -674,28 +674,18 @@ impl<'tcx> chalk_ir::UnificationDatabase<RustInterner<'tcx>> for RustIrDatabase<
         let variances = self.interner.tcx.variances_of(def_id.0);
         chalk_ir::Variances::from_iter(
             self.interner,
-            variances.iter().map(|v| match v {
-                ty::Variance::Invariant => chalk_ir::Variance::Invariant,
-                ty::Variance::Covariant => chalk_ir::Variance::Covariant,
-                ty::Variance::Contravariant => chalk_ir::Variance::Contravariant,
-                ty::Variance::Bivariant => unimplemented!(),
-            }),
+            variances.iter().map(|v| v.lower_into(self.interner)),
         )
     }
 
     fn adt_variance(
         &self,
-        def_id: chalk_ir::AdtId<RustInterner<'tcx>>,
+        adt_id: chalk_ir::AdtId<RustInterner<'tcx>>,
     ) -> chalk_ir::Variances<RustInterner<'tcx>> {
-        let variances = self.interner.tcx.variances_of(def_id.0.did);
+        let variances = self.interner.tcx.variances_of(adt_id.0.did);
         chalk_ir::Variances::from_iter(
             self.interner,
-            variances.iter().map(|v| match v {
-                ty::Variance::Invariant => chalk_ir::Variance::Invariant,
-                ty::Variance::Covariant => chalk_ir::Variance::Covariant,
-                ty::Variance::Contravariant => chalk_ir::Variance::Contravariant,
-                ty::Variance::Bivariant => unimplemented!(),
-            }),
+            variances.iter().map(|v| v.lower_into(self.interner)),
         )
     }
 }

compiler/rustc_traits/src/chalk/lowering.rs

@@ -188,12 +188,18 @@ impl<'tcx> LowerInto<'tcx, chalk_ir::GoalData<RustInterner<'tcx>>> for ty::Predi
                 chalk_ir::DomainGoal::ObjectSafe(chalk_ir::TraitId(t)),
             ),
 
+            ty::PredicateKind::Subtype(ty::SubtypePredicate { a, b, a_is_expected: _ }) => {
+                chalk_ir::GoalData::SubtypeGoal(chalk_ir::SubtypeGoal {
+                    a: a.lower_into(interner),
+                    b: b.lower_into(interner),
+                })
+            }
+
             // FIXME(chalk): other predicates
             //
             // We can defer this, but ultimately we'll want to express
             // some of these in terms of chalk operations.
             ty::PredicateKind::ClosureKind(..)
-            | ty::PredicateKind::Subtype(..)
             | ty::PredicateKind::Coerce(..)
             | ty::PredicateKind::ConstEvaluatable(..)
             | ty::PredicateKind::ConstEquate(..) => {
@@ -790,6 +796,16 @@ impl<'tcx> LowerInto<'tcx, chalk_solve::rust_ir::Polarity> for ty::ImplPolarity
         }
     }
 }
+impl<'tcx> LowerInto<'tcx, chalk_ir::Variance> for ty::Variance {
+    fn lower_into(self, _interner: RustInterner<'tcx>) -> chalk_ir::Variance {
+        match self {
+            ty::Variance::Covariant => chalk_ir::Variance::Covariant,
+            ty::Variance::Invariant => chalk_ir::Variance::Invariant,
+            ty::Variance::Contravariant => chalk_ir::Variance::Contravariant,
+            ty::Variance::Bivariant => unimplemented!(),
+        }
+    }
+}
 
 impl<'tcx> LowerInto<'tcx, chalk_solve::rust_ir::AliasEqBound<RustInterner<'tcx>>>
     for ty::ProjectionPredicate<'tcx>