7 files changed, 26 insertions, 31 deletions

diff --git a/crates/hir_ty/src/db.rs b/crates/hir_ty/src/db.rs
index 91a2e0b5b..58e4247c6 100644
--- a/crates/hir_ty/src/db.rs
+++ b/crates/hir_ty/src/db.rs
@@ -12,8 +12,8 @@ use la_arena::ArenaMap;
 use crate::{
     method_resolution::{InherentImpls, TraitImpls},
     traits::chalk,
-    Binders, CallableDefId, FnDefId, ImplTraitId, InferenceResult, PolyFnSig, ReturnTypeImplTraits,
-    TraitRef, Ty, TyDefId, ValueTyDefId, WhereClause,
+    Binders, CallableDefId, FnDefId, ImplTraitId, InferenceResult, PolyFnSig,
+    QuantifiedWhereClause, ReturnTypeImplTraits, TraitRef, Ty, TyDefId, ValueTyDefId,
 };
 use hir_expand::name::Name;
 
@@ -57,10 +57,13 @@ pub trait HirDatabase: DefDatabase + Upcast<dyn DefDatabase> {
 
     #[salsa::invoke(crate::lower::generic_predicates_for_param_query)]
     #[salsa::cycle(crate::lower::generic_predicates_for_param_recover)]
-    fn generic_predicates_for_param(&self, param_id: TypeParamId) -> Arc<[Binders<WhereClause>]>;
+    fn generic_predicates_for_param(
+        &self,
+        param_id: TypeParamId,
+    ) -> Arc<[Binders<QuantifiedWhereClause>]>;
 
     #[salsa::invoke(crate::lower::generic_predicates_query)]
-    fn generic_predicates(&self, def: GenericDefId) -> Arc<[Binders<WhereClause>]>;
+    fn generic_predicates(&self, def: GenericDefId) -> Arc<[Binders<QuantifiedWhereClause>]>;
 
     #[salsa::invoke(crate::lower::trait_environment_query)]
     fn trait_environment(&self, def: GenericDefId) -> Arc<crate::TraitEnvironment>;
diff --git a/crates/hir_ty/src/display.rs b/crates/hir_ty/src/display.rs
index 372671405..cc6b93d37 100644
--- a/crates/hir_ty/src/display.rs
+++ b/crates/hir_ty/src/display.rs
@@ -581,7 +581,7 @@ impl HirDisplay for Ty {
                             .generic_predicates(id.parent)
                             .into_iter()
                             .map(|pred| pred.clone().subst(&substs))
-                            .filter(|wc| match &wc {
+                            .filter(|wc| match &wc.skip_binders() {
                                 WhereClause::Implemented(tr) => tr.self_type_parameter() == self,
                                 WhereClause::AliasEq(AliasEq {
                                     alias: AliasTy::Projection(proj),
@@ -590,15 +590,7 @@ impl HirDisplay for Ty {
                                 _ => false,
                             })
                             .collect::<Vec<_>>();
-                        write_bounds_like_dyn_trait_with_prefix(
-                            "impl",
-                            &bounds
-                                .iter()
-                                .cloned()
-                                .map(crate::Binders::wrap_empty)
-                                .collect::<Vec<_>>(),
-                            f,
-                        )?;
+                        write_bounds_like_dyn_trait_with_prefix("impl", &bounds, f)?;
                     }
                 }
             }
diff --git a/crates/hir_ty/src/infer/expr.rs b/crates/hir_ty/src/infer/expr.rs
index 79bbc5dab..17849d552 100644
--- a/crates/hir_ty/src/infer/expr.rs
+++ b/crates/hir_ty/src/infer/expr.rs
@@ -11,6 +11,7 @@ use hir_def::{
     AssocContainerId, FieldId, Lookup,
 };
 use hir_expand::name::{name, Name};
+use stdx::always;
 use syntax::ast::RangeOp;
 
 use crate::{
@@ -936,7 +937,9 @@ impl<'a> InferenceContext<'a> {
             let def: CallableDefId = from_chalk(self.db, *fn_def);
             let generic_predicates = self.db.generic_predicates(def.into());
             for predicate in generic_predicates.iter() {
-                let predicate = predicate.clone().subst(parameters);
+                let (predicate, binders) =
+                    predicate.clone().subst(parameters).into_value_and_skipped_binders();
+                always!(binders == 0); // quantified where clauses not yet handled
                 self.obligations.push(predicate.cast(&Interner));
             }
             // add obligation for trait implementation, if this is a trait method
diff --git a/crates/hir_ty/src/lib.rs b/crates/hir_ty/src/lib.rs
index e4b1f92e4..90b5b17e2 100644
--- a/crates/hir_ty/src/lib.rs
+++ b/crates/hir_ty/src/lib.rs
@@ -518,6 +518,10 @@ impl<T> Binders<T> {
     pub fn skip_binders(&self) -> &T {
         &self.value
     }
+
+    pub fn into_value_and_skipped_binders(self) -> (T, usize) {
+        (self.value, self.num_binders)
+    }
 }
 
 impl<T: Clone> Binders<&T> {
@@ -985,7 +989,7 @@ impl Ty {
                             .generic_predicates(id.parent)
                             .into_iter()
                             .map(|pred| pred.clone().subst(&substs))
-                            .filter(|wc| match &wc {
+                            .filter(|wc| match &wc.skip_binders() {
                                 WhereClause::Implemented(tr) => tr.self_type_parameter() == self,
                                 WhereClause::AliasEq(AliasEq {
                                     alias: AliasTy::Projection(proj),
@@ -993,7 +997,6 @@ impl Ty {
                                 }) => proj.self_type_parameter() == self,
                                 _ => false,
                             })
-                            .map(Binders::wrap_empty)
                             .collect_vec();
 
                         Some(predicates)
diff --git a/crates/hir_ty/src/lower.rs b/crates/hir_ty/src/lower.rs
index 45591e920..f60cec649 100644
--- a/crates/hir_ty/src/lower.rs
+++ b/crates/hir_ty/src/lower.rs
@@ -825,7 +825,7 @@ pub fn associated_type_shorthand_candidates<R>(
             let predicates = db.generic_predicates_for_param(param_id);
             let mut traits_: Vec<_> = predicates
                 .iter()
-                .filter_map(|pred| match &pred.value {
+                .filter_map(|pred| match &pred.value.value {
                     WhereClause::Implemented(tr) => Some(tr.clone()),
                     _ => None,
                 })
@@ -898,10 +898,7 @@ pub(crate) fn field_types_query(
 pub(crate) fn generic_predicates_for_param_query(
     db: &dyn HirDatabase,
     param_id: TypeParamId,
-) -> Arc<[Binders<WhereClause>]> {
-    // FIXME: these binders are for the type parameters of the def. We need to
-    // introduce another level of binders for quantified where clauses (for<'a>
-    // ...)
+) -> Arc<[Binders<QuantifiedWhereClause>]> {
     let resolver = param_id.parent.resolver(db.upcast());
     let ctx =
         TyLoweringContext::new(db, &resolver).with_type_param_mode(TypeParamLoweringMode::Variable);
@@ -920,7 +917,7 @@ pub(crate) fn generic_predicates_for_param_query(
             WherePredicate::Lifetime { .. } => false,
         })
         .flat_map(|pred| {
-            ctx.lower_where_predicate(pred, true).map(|p| Binders::new(generics.len(), p.value))
+            ctx.lower_where_predicate(pred, true).map(|p| Binders::new(generics.len(), p))
         })
         .collect()
 }
@@ -929,7 +926,7 @@ pub(crate) fn generic_predicates_for_param_recover(
     _db: &dyn HirDatabase,
     _cycle: &[String],
     _param_id: &TypeParamId,
-) -> Arc<[Binders<WhereClause>]> {
+) -> Arc<[Binders<QuantifiedWhereClause>]> {
     Arc::new([])
 }
 
@@ -984,10 +981,7 @@ pub(crate) fn trait_environment_query(
 pub(crate) fn generic_predicates_query(
     db: &dyn HirDatabase,
     def: GenericDefId,
-) -> Arc<[Binders<WhereClause>]> {
-    // FIXME: these binders are for the type parameters of the def. We need to
-    // introduce another level of binders for quantified where clauses (for<'a>
-    // ...)
+) -> Arc<[Binders<QuantifiedWhereClause>]> {
     let resolver = def.resolver(db.upcast());
     let ctx =
         TyLoweringContext::new(db, &resolver).with_type_param_mode(TypeParamLoweringMode::Variable);
@@ -995,7 +989,7 @@ pub(crate) fn generic_predicates_query(
     resolver
         .where_predicates_in_scope()
         .flat_map(|pred| {
-            ctx.lower_where_predicate(pred, false).map(|p| Binders::new(generics.len(), p.value))
+            ctx.lower_where_predicate(pred, false).map(|p| Binders::new(generics.len(), p))
         })
         .collect()
 }
diff --git a/crates/hir_ty/src/traits/chalk/mapping.rs b/crates/hir_ty/src/traits/chalk/mapping.rs
index 5b9c7e831..7209dd14e 100644
--- a/crates/hir_ty/src/traits/chalk/mapping.rs
+++ b/crates/hir_ty/src/traits/chalk/mapping.rs
@@ -537,7 +537,7 @@ pub(super) fn convert_where_clauses(
     let generic_predicates = db.generic_predicates(def);
     let mut result = Vec::with_capacity(generic_predicates.len());
     for pred in generic_predicates.iter() {
-        result.push(crate::Binders::wrap_empty(pred.clone().subst(substs)).to_chalk(db));
+        result.push(pred.clone().subst(substs).to_chalk(db));
     }
     result
 }
diff --git a/crates/hir_ty/src/utils.rs b/crates/hir_ty/src/utils.rs
index 1ec1ecd43..19874e42b 100644
--- a/crates/hir_ty/src/utils.rs
+++ b/crates/hir_ty/src/utils.rs
@@ -63,7 +63,7 @@ fn direct_super_trait_refs(db: &dyn HirDatabase, trait_ref: &TraitRef) -> Vec<Tr
     db.generic_predicates_for_param(trait_self)
         .iter()
         .filter_map(|pred| {
-            pred.as_ref().filter_map(|pred| match pred {
+            pred.as_ref().filter_map(|pred| match pred.skip_binders() {
                 WhereClause::Implemented(tr) => Some(tr.clone()),
                 _ => None,
             })