]> git.lizzy.rs Git - rust.git/blobdiff - crates/hir_ty/src/lower.rs
Rename TyKind::ForeignType to Foreign
[rust.git] / crates / hir_ty / src / lower.rs
index 78a914cacee34565795e041650770af1dddda914..ba48be4ad0f1daa924e448898a3b8b9d6b3127ba 100644 (file)
@@ -8,14 +8,14 @@
 use std::{iter, sync::Arc};
 
 use base_db::CrateId;
-use chalk_ir::{cast::Cast, Mutability};
+use chalk_ir::{cast::Cast, Mutability, Safety};
 use hir_def::{
     adt::StructKind,
     builtin_type::BuiltinType,
     generics::{TypeParamProvenance, WherePredicate, WherePredicateTypeTarget},
     path::{GenericArg, Path, PathSegment, PathSegments},
     resolver::{HasResolver, Resolver, TypeNs},
-    type_ref::{TypeBound, TypeRef},
+    type_ref::{TraitRef as HirTraitRef, TypeBound, TypeRef},
     AdtId, AssocContainerId, AssocItemId, ConstId, ConstParamId, EnumId, EnumVariantId, FunctionId,
     GenericDefId, HasModule, ImplId, LocalFieldId, Lookup, StaticId, StructId, TraitId,
     TypeAliasId, TypeParamId, UnionId, VariantId,
 
 use crate::{
     db::HirDatabase,
-    to_assoc_type_id, to_placeholder_idx,
+    to_assoc_type_id, to_chalk_trait_id, to_placeholder_idx,
     traits::chalk::{Interner, ToChalk},
     utils::{
         all_super_trait_refs, associated_type_by_name_including_super_traits, generics,
-        make_mut_slice, variant_data,
+        variant_data,
     },
-    AliasTy, Binders, BoundVar, CallableSig, DebruijnIndex, FnPointer, FnSig, GenericPredicate,
-    OpaqueTy, OpaqueTyId, PolyFnSig, ProjectionPredicate, ProjectionTy, ReturnTypeImplTrait,
-    ReturnTypeImplTraits, Substs, TraitEnvironment, TraitRef, Ty, TyKind, TypeWalk,
+    AliasEq, AliasTy, Binders, BoundVar, CallableSig, DebruijnIndex, DynTy, FnPointer, FnSig,
+    ImplTraitId, OpaqueTy, PolyFnSig, ProjectionTy, QuantifiedWhereClause, QuantifiedWhereClauses,
+    ReturnTypeImplTrait, ReturnTypeImplTraits, Substitution, TraitEnvironment, TraitRef, Ty,
+    TyBuilder, TyKind, TypeWalk, WhereClause,
 };
 
 #[derive(Debug)]
@@ -140,47 +141,48 @@ pub enum TypeParamLoweringMode {
     Variable,
 }
 
-impl Ty {
-    pub fn from_hir(ctx: &TyLoweringContext<'_>, type_ref: &TypeRef) -> Self {
-        Ty::from_hir_ext(ctx, type_ref).0
+impl<'a> TyLoweringContext<'a> {
+    pub fn lower_ty(&self, type_ref: &TypeRef) -> Ty {
+        self.lower_ty_ext(type_ref).0
     }
-    pub fn from_hir_ext(ctx: &TyLoweringContext<'_>, type_ref: &TypeRef) -> (Self, Option<TypeNs>) {
+
+    pub fn lower_ty_ext(&self, type_ref: &TypeRef) -> (Ty, Option<TypeNs>) {
         let mut res = None;
         let ty = match type_ref {
             TypeRef::Never => TyKind::Never.intern(&Interner),
             TypeRef::Tuple(inner) => {
-                let inner_tys: Arc<[Ty]> = inner.iter().map(|tr| Ty::from_hir(ctx, tr)).collect();
-                TyKind::Tuple(inner_tys.len(), Substs(inner_tys)).intern(&Interner)
+                let inner_tys = inner.iter().map(|tr| self.lower_ty(tr));
+                TyKind::Tuple(inner_tys.len(), Substitution::from_iter(&Interner, inner_tys))
+                    .intern(&Interner)
             }
             TypeRef::Path(path) => {
-                let (ty, res_) = Ty::from_hir_path(ctx, path);
+                let (ty, res_) = self.lower_path(path);
                 res = res_;
                 ty
             }
             TypeRef::RawPtr(inner, mutability) => {
-                let inner_ty = Ty::from_hir(ctx, inner);
-                TyKind::Raw(lower_to_chalk_mutability(*mutability), Substs::single(inner_ty))
-                    .intern(&Interner)
+                let inner_ty = self.lower_ty(inner);
+                TyKind::Raw(lower_to_chalk_mutability(*mutability), inner_ty).intern(&Interner)
             }
             TypeRef::Array(inner) => {
-                let inner_ty = Ty::from_hir(ctx, inner);
-                TyKind::Array(Substs::single(inner_ty)).intern(&Interner)
+                let inner_ty = self.lower_ty(inner);
+                TyKind::Array(inner_ty).intern(&Interner)
             }
             TypeRef::Slice(inner) => {
-                let inner_ty = Ty::from_hir(ctx, inner);
-                TyKind::Slice(Substs::single(inner_ty)).intern(&Interner)
+                let inner_ty = self.lower_ty(inner);
+                TyKind::Slice(inner_ty).intern(&Interner)
             }
             TypeRef::Reference(inner, _, mutability) => {
-                let inner_ty = Ty::from_hir(ctx, inner);
-                TyKind::Ref(lower_to_chalk_mutability(*mutability), Substs::single(inner_ty))
-                    .intern(&Interner)
+                let inner_ty = self.lower_ty(inner);
+                TyKind::Ref(lower_to_chalk_mutability(*mutability), inner_ty).intern(&Interner)
             }
-            TypeRef::Placeholder => TyKind::Unknown.intern(&Interner),
+            TypeRef::Placeholder => TyKind::Error.intern(&Interner),
             TypeRef::Fn(params, is_varargs) => {
-                let substs = Substs(params.iter().map(|tr| Ty::from_hir(ctx, tr)).collect());
+                let substs =
+                    Substitution::from_iter(&Interner, params.iter().map(|tr| self.lower_ty(tr)));
                 TyKind::Function(FnPointer {
-                    num_args: substs.len() - 1,
-                    sig: FnSig { variadic: *is_varargs },
+                    num_args: substs.len(&Interner) - 1,
+                    sig: FnSig { abi: (), safety: Safety::Safe, variadic: *is_varargs },
                     substs,
                 })
                 .intern(&Interner)
@@ -188,25 +190,26 @@ pub fn from_hir_ext(ctx: &TyLoweringContext<'_>, type_ref: &TypeRef) -> (Self, O
             TypeRef::DynTrait(bounds) => {
                 let self_ty =
                     TyKind::BoundVar(BoundVar::new(DebruijnIndex::INNERMOST, 0)).intern(&Interner);
-                let predicates = ctx.with_shifted_in(DebruijnIndex::ONE, |ctx| {
-                    bounds
-                        .iter()
-                        .flat_map(|b| GenericPredicate::from_type_bound(ctx, b, self_ty.clone()))
-                        .collect()
+                let bounds = self.with_shifted_in(DebruijnIndex::ONE, |ctx| {
+                    QuantifiedWhereClauses::from_iter(
+                        &Interner,
+                        bounds.iter().flat_map(|b| ctx.lower_type_bound(b, self_ty.clone(), false)),
+                    )
                 });
-                TyKind::Dyn(predicates).intern(&Interner)
+                let bounds = Binders::new(1, bounds);
+                TyKind::Dyn(DynTy { bounds }).intern(&Interner)
             }
             TypeRef::ImplTrait(bounds) => {
-                match ctx.impl_trait_mode {
+                match self.impl_trait_mode {
                     ImplTraitLoweringMode::Opaque => {
-                        let idx = ctx.impl_trait_counter.get();
-                        ctx.impl_trait_counter.set(idx + 1);
+                        let idx = self.impl_trait_counter.get();
+                        self.impl_trait_counter.set(idx + 1);
 
-                        assert!(idx as usize == ctx.opaque_type_data.borrow().len());
+                        assert!(idx as usize == self.opaque_type_data.borrow().len());
                         // this dance is to make sure the data is in the right
                         // place even if we encounter more opaque types while
                         // lowering the bounds
-                        ctx.opaque_type_data
+                        self.opaque_type_data
                             .borrow_mut()
                             .push(ReturnTypeImplTrait { bounds: Binders::new(1, Vec::new()) });
                         // We don't want to lower the bounds inside the binders
@@ -218,69 +221,70 @@ pub fn from_hir_ext(ctx: &TyLoweringContext<'_>, type_ref: &TypeRef) -> (Self, O
                         // other, but separately. So if the `T` refers to a type
                         // parameter of the outer function, it's just one binder
                         // away instead of two.
-                        let actual_opaque_type_data = ctx
+                        let actual_opaque_type_data = self
                             .with_debruijn(DebruijnIndex::INNERMOST, |ctx| {
-                                ReturnTypeImplTrait::from_hir(ctx, &bounds)
+                                ctx.lower_impl_trait(&bounds)
                             });
-                        ctx.opaque_type_data.borrow_mut()[idx as usize] = actual_opaque_type_data;
+                        self.opaque_type_data.borrow_mut()[idx as usize] = actual_opaque_type_data;
 
-                        let func = match ctx.resolver.generic_def() {
+                        let func = match self.resolver.generic_def() {
                             Some(GenericDefId::FunctionId(f)) => f,
                             _ => panic!("opaque impl trait lowering in non-function"),
                         };
-                        let impl_trait_id = OpaqueTyId::ReturnTypeImplTrait(func, idx);
-                        let generics = generics(ctx.db.upcast(), func.into());
-                        let parameters = Substs::bound_vars(&generics, ctx.in_binders);
+                        let impl_trait_id = ImplTraitId::ReturnTypeImplTrait(func, idx);
+                        let opaque_ty_id = self.db.intern_impl_trait_id(impl_trait_id).into();
+                        let generics = generics(self.db.upcast(), func.into());
+                        let parameters = generics.bound_vars_subst(self.in_binders);
                         TyKind::Alias(AliasTy::Opaque(OpaqueTy {
-                            opaque_ty_id: impl_trait_id,
-                            parameters,
+                            opaque_ty_id,
+                            substitution: parameters,
                         }))
                         .intern(&Interner)
                     }
                     ImplTraitLoweringMode::Param => {
-                        let idx = ctx.impl_trait_counter.get();
+                        let idx = self.impl_trait_counter.get();
                         // FIXME we're probably doing something wrong here
-                        ctx.impl_trait_counter.set(idx + count_impl_traits(type_ref) as u16);
-                        if let Some(def) = ctx.resolver.generic_def() {
-                            let generics = generics(ctx.db.upcast(), def);
+                        self.impl_trait_counter.set(idx + count_impl_traits(type_ref) as u16);
+                        if let Some(def) = self.resolver.generic_def() {
+                            let generics = generics(self.db.upcast(), def);
                             let param = generics
                                 .iter()
                                 .filter(|(_, data)| {
                                     data.provenance == TypeParamProvenance::ArgumentImplTrait
                                 })
                                 .nth(idx as usize)
-                                .map_or(TyKind::Unknown, |(id, _)| {
-                                    TyKind::Placeholder(to_placeholder_idx(ctx.db, id))
+                                .map_or(TyKind::Error, |(id, _)| {
+                                    TyKind::Placeholder(to_placeholder_idx(self.db, id))
                                 });
                             param.intern(&Interner)
                         } else {
-                            TyKind::Unknown.intern(&Interner)
+                            TyKind::Error.intern(&Interner)
                         }
                     }
                     ImplTraitLoweringMode::Variable => {
-                        let idx = ctx.impl_trait_counter.get();
+                        let idx = self.impl_trait_counter.get();
                         // FIXME we're probably doing something wrong here
-                        ctx.impl_trait_counter.set(idx + count_impl_traits(type_ref) as u16);
+                        self.impl_trait_counter.set(idx + count_impl_traits(type_ref) as u16);
                         let (parent_params, self_params, list_params, _impl_trait_params) =
-                            if let Some(def) = ctx.resolver.generic_def() {
-                                let generics = generics(ctx.db.upcast(), def);
+                            if let Some(def) = self.resolver.generic_def() {
+                                let generics = generics(self.db.upcast(), def);
                                 generics.provenance_split()
                             } else {
                                 (0, 0, 0, 0)
                             };
                         TyKind::BoundVar(BoundVar::new(
-                            ctx.in_binders,
+                            self.in_binders,
                             idx as usize + parent_params + self_params + list_params,
                         ))
                         .intern(&Interner)
                     }
                     ImplTraitLoweringMode::Disallowed => {
                         // FIXME: report error
-                        TyKind::Unknown.intern(&Interner)
+                        TyKind::Error.intern(&Interner)
                     }
                 }
             }
-            TypeRef::Error => TyKind::Unknown.intern(&Interner),
+            TypeRef::Error => TyKind::Error.intern(&Interner),
         };
         (ty, res)
     }
@@ -288,7 +292,7 @@ pub fn from_hir_ext(ctx: &TyLoweringContext<'_>, type_ref: &TypeRef) -> (Self, O
     /// This is only for `generic_predicates_for_param`, where we can't just
     /// lower the self types of the predicates since that could lead to cycles.
     /// So we just check here if the `type_ref` resolves to a generic param, and which.
-    fn from_hir_only_param(ctx: &TyLoweringContext<'_>, type_ref: &TypeRef) -> Option<TypeParamId> {
+    fn lower_ty_only_param(&self, type_ref: &TypeRef) -> Option<TypeParamId> {
         let path = match type_ref {
             TypeRef::Path(path) => path,
             _ => return None,
@@ -300,7 +304,7 @@ fn from_hir_only_param(ctx: &TyLoweringContext<'_>, type_ref: &TypeRef) -> Optio
             return None;
         }
         let resolution =
-            match ctx.resolver.resolve_path_in_type_ns(ctx.db.upcast(), path.mod_path()) {
+            match self.resolver.resolve_path_in_type_ns(self.db.upcast(), path.mod_path()) {
                 Some((it, None)) => it,
                 _ => return None,
             };
@@ -311,8 +315,8 @@ fn from_hir_only_param(ctx: &TyLoweringContext<'_>, type_ref: &TypeRef) -> Optio
         }
     }
 
-    pub(crate) fn from_type_relative_path(
-        ctx: &TyLoweringContext<'_>,
+    pub(crate) fn lower_ty_relative_path(
+        &self,
         ty: Ty,
         // We need the original resolution to lower `Self::AssocTy` correctly
         res: Option<TypeNs>,
@@ -321,17 +325,17 @@ pub(crate) fn from_type_relative_path(
         if remaining_segments.len() == 1 {
             // resolve unselected assoc types
             let segment = remaining_segments.first().unwrap();
-            (Ty::select_associated_type(ctx, res, segment), None)
+            (self.select_associated_type(res, segment), None)
         } else if remaining_segments.len() > 1 {
             // FIXME report error (ambiguous associated type)
-            (TyKind::Unknown.intern(&Interner), None)
+            (TyKind::Error.intern(&Interner), None)
         } else {
             (ty, res)
         }
     }
 
-    pub(crate) fn from_partly_resolved_hir_path(
-        ctx: &TyLoweringContext<'_>,
+    pub(crate) fn lower_partly_resolved_path(
+        &self,
         resolution: TypeNs,
         resolved_segment: PathSegment<'_>,
         remaining_segments: PathSegments<'_>,
@@ -349,11 +353,11 @@ pub(crate) fn from_partly_resolved_hir_path(
                     None
                 };
                 let trait_ref =
-                    TraitRef::from_resolved_path(ctx, trait_, resolved_segment, self_ty);
+                    self.lower_trait_ref_from_resolved_path(trait_, resolved_segment, self_ty);
                 let ty = if remaining_segments.len() == 1 {
                     let segment = remaining_segments.first().unwrap();
                     let found = associated_type_by_name_including_super_traits(
-                        ctx.db,
+                        self.db,
                         trait_ref,
                         &segment.name,
                     );
@@ -361,91 +365,89 @@ pub(crate) fn from_partly_resolved_hir_path(
                         Some((super_trait_ref, associated_ty)) => {
                             // FIXME handle type parameters on the segment
                             TyKind::Alias(AliasTy::Projection(ProjectionTy {
-                                associated_ty: to_assoc_type_id(associated_ty),
-                                parameters: super_trait_ref.substs,
+                                associated_ty_id: to_assoc_type_id(associated_ty),
+                                substitution: super_trait_ref.substitution,
                             }))
                             .intern(&Interner)
                         }
                         None => {
                             // FIXME: report error (associated type not found)
-                            TyKind::Unknown.intern(&Interner)
+                            TyKind::Error.intern(&Interner)
                         }
                     }
                 } else if remaining_segments.len() > 1 {
                     // FIXME report error (ambiguous associated type)
-                    TyKind::Unknown.intern(&Interner)
+                    TyKind::Error.intern(&Interner)
                 } else {
-                    TyKind::Dyn(Arc::new([GenericPredicate::Implemented(trait_ref)]))
-                        .intern(&Interner)
+                    let dyn_ty = DynTy {
+                        bounds: Binders::new(
+                            1,
+                            QuantifiedWhereClauses::from_iter(
+                                &Interner,
+                                Some(Binders::wrap_empty(WhereClause::Implemented(trait_ref))),
+                            ),
+                        ),
+                    };
+                    TyKind::Dyn(dyn_ty).intern(&Interner)
                 };
                 return (ty, None);
             }
             TypeNs::GenericParam(param_id) => {
                 let generics = generics(
-                    ctx.db.upcast(),
-                    ctx.resolver.generic_def().expect("generics in scope"),
+                    self.db.upcast(),
+                    self.resolver.generic_def().expect("generics in scope"),
                 );
-                match ctx.type_param_mode {
+                match self.type_param_mode {
                     TypeParamLoweringMode::Placeholder => {
-                        TyKind::Placeholder(to_placeholder_idx(ctx.db, param_id))
+                        TyKind::Placeholder(to_placeholder_idx(self.db, param_id))
                     }
                     TypeParamLoweringMode::Variable => {
                         let idx = generics.param_idx(param_id).expect("matching generics");
-                        TyKind::BoundVar(BoundVar::new(ctx.in_binders, idx))
+                        TyKind::BoundVar(BoundVar::new(self.in_binders, idx))
                     }
                 }
                 .intern(&Interner)
             }
             TypeNs::SelfType(impl_id) => {
-                let generics = generics(ctx.db.upcast(), impl_id.into());
-                let substs = match ctx.type_param_mode {
-                    TypeParamLoweringMode::Placeholder => {
-                        Substs::type_params_for_generics(ctx.db, &generics)
-                    }
-                    TypeParamLoweringMode::Variable => {
-                        Substs::bound_vars(&generics, ctx.in_binders)
-                    }
+                let generics = generics(self.db.upcast(), impl_id.into());
+                let substs = match self.type_param_mode {
+                    TypeParamLoweringMode::Placeholder => generics.type_params_subst(self.db),
+                    TypeParamLoweringMode::Variable => generics.bound_vars_subst(self.in_binders),
                 };
-                ctx.db.impl_self_ty(impl_id).subst(&substs)
+                self.db.impl_self_ty(impl_id).subst(&substs)
             }
             TypeNs::AdtSelfType(adt) => {
-                let generics = generics(ctx.db.upcast(), adt.into());
-                let substs = match ctx.type_param_mode {
-                    TypeParamLoweringMode::Placeholder => {
-                        Substs::type_params_for_generics(ctx.db, &generics)
-                    }
-                    TypeParamLoweringMode::Variable => {
-                        Substs::bound_vars(&generics, ctx.in_binders)
-                    }
+                let generics = generics(self.db.upcast(), adt.into());
+                let substs = match self.type_param_mode {
+                    TypeParamLoweringMode::Placeholder => generics.type_params_subst(self.db),
+                    TypeParamLoweringMode::Variable => generics.bound_vars_subst(self.in_binders),
                 };
-                ctx.db.ty(adt.into()).subst(&substs)
+                self.db.ty(adt.into()).subst(&substs)
             }
 
-            TypeNs::AdtId(it) => {
-                Ty::from_hir_path_inner(ctx, resolved_segment, it.into(), infer_args)
-            }
+            TypeNs::AdtId(it) => self.lower_path_inner(resolved_segment, it.into(), infer_args),
             TypeNs::BuiltinType(it) => {
-                Ty::from_hir_path_inner(ctx, resolved_segment, it.into(), infer_args)
+                self.lower_path_inner(resolved_segment, it.into(), infer_args)
             }
             TypeNs::TypeAliasId(it) => {
-                Ty::from_hir_path_inner(ctx, resolved_segment, it.into(), infer_args)
+                self.lower_path_inner(resolved_segment, it.into(), infer_args)
             }
             // FIXME: report error
-            TypeNs::EnumVariantId(_) => return (TyKind::Unknown.intern(&Interner), None),
+            TypeNs::EnumVariantId(_) => return (TyKind::Error.intern(&Interner), None),
         };
-        Ty::from_type_relative_path(ctx, ty, Some(resolution), remaining_segments)
+        self.lower_ty_relative_path(ty, Some(resolution), remaining_segments)
     }
 
-    pub(crate) fn from_hir_path(ctx: &TyLoweringContext<'_>, path: &Path) -> (Ty, Option<TypeNs>) {
+    pub(crate) fn lower_path(&self, path: &Path) -> (Ty, Option<TypeNs>) {
         // Resolve the path (in type namespace)
         if let Some(type_ref) = path.type_anchor() {
-            let (ty, res) = Ty::from_hir_ext(ctx, &type_ref);
-            return Ty::from_type_relative_path(ctx, ty, res, path.segments());
+            let (ty, res) = self.lower_ty_ext(&type_ref);
+            return self.lower_ty_relative_path(ty, res, path.segments());
         }
         let (resolution, remaining_index) =
-            match ctx.resolver.resolve_path_in_type_ns(ctx.db.upcast(), path.mod_path()) {
+            match self.resolver.resolve_path_in_type_ns(self.db.upcast(), path.mod_path()) {
                 Some(it) => it,
-                None => return (TyKind::Unknown.intern(&Interner), None),
+                None => return (TyKind::Error.intern(&Interner), None),
             };
         let (resolved_segment, remaining_segments) = match remaining_index {
             None => (
@@ -454,62 +456,56 @@ pub(crate) fn from_hir_path(ctx: &TyLoweringContext<'_>, path: &Path) -> (Ty, Op
             ),
             Some(i) => (path.segments().get(i - 1).unwrap(), path.segments().skip(i)),
         };
-        Ty::from_partly_resolved_hir_path(
-            ctx,
-            resolution,
-            resolved_segment,
-            remaining_segments,
-            false,
-        )
+        self.lower_partly_resolved_path(resolution, resolved_segment, remaining_segments, false)
     }
 
-    fn select_associated_type(
-        ctx: &TyLoweringContext<'_>,
-        res: Option<TypeNs>,
-        segment: PathSegment<'_>,
-    ) -> Ty {
+    fn select_associated_type(&self, res: Option<TypeNs>, segment: PathSegment<'_>) -> Ty {
         if let Some(res) = res {
-            let ty =
-                associated_type_shorthand_candidates(ctx.db, res, move |name, t, associated_ty| {
+            let ty = associated_type_shorthand_candidates(
+                self.db,
+                res,
+                move |name, t, associated_ty| {
                     if name == segment.name {
-                        let substs = match ctx.type_param_mode {
+                        let substs = match self.type_param_mode {
                             TypeParamLoweringMode::Placeholder => {
                                 // if we're lowering to placeholders, we have to put
                                 // them in now
-                                let s = Substs::type_params(
-                                    ctx.db,
-                                    ctx.resolver.generic_def().expect(
+                                let generics = generics(
+                                    self.db.upcast(),
+                                    self.resolver.generic_def().expect(
                                         "there should be generics if there's a generic param",
                                     ),
                                 );
-                                t.substs.clone().subst_bound_vars(&s)
+                                let s = generics.type_params_subst(self.db);
+                                t.substitution.clone().subst_bound_vars(&s)
                             }
-                            TypeParamLoweringMode::Variable => t.substs.clone(),
+                            TypeParamLoweringMode::Variable => t.substitution.clone(),
                         };
                         // We need to shift in the bound vars, since
                         // associated_type_shorthand_candidates does not do that
-                        let substs = substs.shift_bound_vars(ctx.in_binders);
+                        let substs = substs.shift_bound_vars(self.in_binders);
                         // FIXME handle type parameters on the segment
                         return Some(
                             TyKind::Alias(AliasTy::Projection(ProjectionTy {
-                                associated_ty: to_assoc_type_id(associated_ty),
-                                parameters: substs,
+                                associated_ty_id: to_assoc_type_id(associated_ty),
+                                substitution: substs,
                             }))
                             .intern(&Interner),
                         );
                     }
 
                     None
-                });
+                },
+            );
 
-            ty.unwrap_or(TyKind::Unknown.intern(&Interner))
+            ty.unwrap_or(TyKind::Error.intern(&Interner))
         } else {
-            TyKind::Unknown.intern(&Interner)
+            TyKind::Error.intern(&Interner)
         }
     }
 
-    fn from_hir_path_inner(
-        ctx: &TyLoweringContext<'_>,
+    fn lower_path_inner(
+        &self,
         segment: PathSegment<'_>,
         typeable: TyDefId,
         infer_args: bool,
@@ -519,21 +515,21 @@ fn from_hir_path_inner(
             TyDefId::AdtId(it) => Some(it.into()),
             TyDefId::TypeAliasId(it) => Some(it.into()),
         };
-        let substs = substs_from_path_segment(ctx, segment, generic_def, infer_args);
-        ctx.db.ty(typeable).subst(&substs)
+        let substs = self.substs_from_path_segment(segment, generic_def, infer_args, None);
+        self.db.ty(typeable).subst(&substs)
     }
 
     /// Collect generic arguments from a path into a `Substs`. See also
     /// `create_substs_for_ast_path` and `def_to_ty` in rustc.
     pub(super) fn substs_from_path(
-        ctx: &TyLoweringContext<'_>,
+        &self,
         path: &Path,
         // Note that we don't call `db.value_type(resolved)` here,
         // `ValueTyDefId` is just a convenient way to pass generics and
         // special-case enum variants
         resolved: ValueTyDefId,
         infer_args: bool,
-    ) -> Substs {
+    ) -> Substitution {
         let last = path.segments().last().expect("path should have at least one segment");
         let (segment, generic_def) = match resolved {
             ValueTyDefId::FunctionId(it) => (last, Some(it.into())),
@@ -556,145 +552,147 @@ pub(super) fn substs_from_path(
                 (segment, Some(var.parent.into()))
             }
         };
-        substs_from_path_segment(ctx, segment, generic_def, infer_args)
+        self.substs_from_path_segment(segment, generic_def, infer_args, None)
     }
-}
 
-fn substs_from_path_segment(
-    ctx: &TyLoweringContext<'_>,
-    segment: PathSegment<'_>,
-    def_generic: Option<GenericDefId>,
-    infer_args: bool,
-) -> Substs {
-    let mut substs = Vec::new();
-    let def_generics = def_generic.map(|def| generics(ctx.db.upcast(), def));
+    fn substs_from_path_segment(
+        &self,
+        segment: PathSegment<'_>,
+        def_generic: Option<GenericDefId>,
+        infer_args: bool,
+        explicit_self_ty: Option<Ty>,
+    ) -> Substitution {
+        let mut substs = Vec::new();
+        let def_generics = def_generic.map(|def| generics(self.db.upcast(), def));
 
-    let (parent_params, self_params, type_params, impl_trait_params) =
-        def_generics.map_or((0, 0, 0, 0), |g| g.provenance_split());
-    let total_len = parent_params + self_params + type_params + impl_trait_params;
+        let (parent_params, self_params, type_params, impl_trait_params) =
+            def_generics.map_or((0, 0, 0, 0), |g| g.provenance_split());
+        let total_len = parent_params + self_params + type_params + impl_trait_params;
 
-    substs.extend(iter::repeat(TyKind::Unknown.intern(&Interner)).take(parent_params));
+        substs.extend(iter::repeat(TyKind::Error.intern(&Interner)).take(parent_params));
 
-    let mut had_explicit_type_args = false;
+        let fill_self_params = || {
+            substs.extend(
+                explicit_self_ty
+                    .into_iter()
+                    .chain(iter::repeat(TyKind::Error.intern(&Interner)))
+                    .take(self_params),
+            )
+        };
+        let mut had_explicit_type_args = false;
 
-    if let Some(generic_args) = &segment.args_and_bindings {
-        if !generic_args.has_self_type {
-            substs.extend(iter::repeat(TyKind::Unknown.intern(&Interner)).take(self_params));
-        }
-        let expected_num =
-            if generic_args.has_self_type { self_params + type_params } else { type_params };
-        let skip = if generic_args.has_self_type && self_params == 0 { 1 } else { 0 };
-        // if args are provided, it should be all of them, but we can't rely on that
-        for arg in generic_args
-            .args
-            .iter()
-            .filter(|arg| matches!(arg, GenericArg::Type(_)))
-            .skip(skip)
-            .take(expected_num)
-        {
-            match arg {
-                GenericArg::Type(type_ref) => {
-                    had_explicit_type_args = true;
-                    let ty = Ty::from_hir(ctx, type_ref);
-                    substs.push(ty);
+        if let Some(generic_args) = &segment.args_and_bindings {
+            if !generic_args.has_self_type {
+                fill_self_params();
+            }
+            let expected_num =
+                if generic_args.has_self_type { self_params + type_params } else { type_params };
+            let skip = if generic_args.has_self_type && self_params == 0 { 1 } else { 0 };
+            // if args are provided, it should be all of them, but we can't rely on that
+            for arg in generic_args
+                .args
+                .iter()
+                .filter(|arg| matches!(arg, GenericArg::Type(_)))
+                .skip(skip)
+                .take(expected_num)
+            {
+                match arg {
+                    GenericArg::Type(type_ref) => {
+                        had_explicit_type_args = true;
+                        let ty = self.lower_ty(type_ref);
+                        substs.push(ty);
+                    }
+                    GenericArg::Lifetime(_) => {}
                 }
-                GenericArg::Lifetime(_) => {}
             }
+        } else {
+            fill_self_params();
         }
-    }
 
-    // handle defaults. In expression or pattern path segments without
-    // explicitly specified type arguments, missing type arguments are inferred
-    // (i.e. defaults aren't used).
-    if !infer_args || had_explicit_type_args {
-        if let Some(def_generic) = def_generic {
-            let defaults = ctx.db.generic_defaults(def_generic);
-            assert_eq!(total_len, defaults.len());
-
-            for default_ty in defaults.iter().skip(substs.len()) {
-                // each default can depend on the previous parameters
-                let substs_so_far = Substs(substs.clone().into());
-                substs.push(default_ty.clone().subst(&substs_so_far));
+        // handle defaults. In expression or pattern path segments without
+        // explicitly specified type arguments, missing type arguments are inferred
+        // (i.e. defaults aren't used).
+        if !infer_args || had_explicit_type_args {
+            if let Some(def_generic) = def_generic {
+                let defaults = self.db.generic_defaults(def_generic);
+                assert_eq!(total_len, defaults.len());
+
+                for default_ty in defaults.iter().skip(substs.len()) {
+                    // each default can depend on the previous parameters
+                    let substs_so_far = Substitution::from_iter(&Interner, substs.clone());
+                    substs.push(default_ty.clone().subst(&substs_so_far));
+                }
             }
         }
-    }
 
-    // add placeholders for args that were not provided
-    // FIXME: emit diagnostics in contexts where this is not allowed
-    for _ in substs.len()..total_len {
-        substs.push(TyKind::Unknown.intern(&Interner));
-    }
-    assert_eq!(substs.len(), total_len);
+        // add placeholders for args that were not provided
+        // FIXME: emit diagnostics in contexts where this is not allowed
+        for _ in substs.len()..total_len {
+            substs.push(TyKind::Error.intern(&Interner));
+        }
+        assert_eq!(substs.len(), total_len);
 
-    Substs(substs.into())
-}
+        Substitution::from_iter(&Interner, substs)
+    }
 
-impl TraitRef {
-    fn from_path(
-        ctx: &TyLoweringContext<'_>,
+    fn lower_trait_ref_from_path(
+        &self,
         path: &Path,
         explicit_self_ty: Option<Ty>,
-    ) -> Option<Self> {
+    ) -> Option<TraitRef> {
         let resolved =
-            match ctx.resolver.resolve_path_in_type_ns_fully(ctx.db.upcast(), path.mod_path())? {
+            match self.resolver.resolve_path_in_type_ns_fully(self.db.upcast(), path.mod_path())? {
                 TypeNs::TraitId(tr) => tr,
                 _ => return None,
             };
         let segment = path.segments().last().expect("path should have at least one segment");
-        Some(TraitRef::from_resolved_path(ctx, resolved, segment, explicit_self_ty))
+        Some(self.lower_trait_ref_from_resolved_path(resolved, segment, explicit_self_ty))
     }
 
-    pub(crate) fn from_resolved_path(
-        ctx: &TyLoweringContext<'_>,
+    pub(crate) fn lower_trait_ref_from_resolved_path(
+        &self,
         resolved: TraitId,
         segment: PathSegment<'_>,
         explicit_self_ty: Option<Ty>,
-    ) -> Self {
-        let mut substs = TraitRef::substs_from_path(ctx, segment, resolved);
-        if let Some(self_ty) = explicit_self_ty {
-            make_mut_slice(&mut substs.0)[0] = self_ty;
-        }
-        TraitRef { trait_: resolved, substs }
+    ) -> TraitRef {
+        let substs = self.trait_ref_substs_from_path(segment, resolved, explicit_self_ty);
+        TraitRef { trait_id: to_chalk_trait_id(resolved), substitution: substs }
     }
 
-    fn from_hir(
-        ctx: &TyLoweringContext<'_>,
-        type_ref: &TypeRef,
+    fn lower_trait_ref(
+        &self,
+        trait_ref: &HirTraitRef,
         explicit_self_ty: Option<Ty>,
-    ) -> Option<Self> {
-        let path = match type_ref {
-            TypeRef::Path(path) => path,
-            _ => return None,
-        };
-        TraitRef::from_path(ctx, path, explicit_self_ty)
+    ) -> Option<TraitRef> {
+        self.lower_trait_ref_from_path(&trait_ref.path, explicit_self_ty)
     }
 
-    fn substs_from_path(
-        ctx: &TyLoweringContext<'_>,
+    fn trait_ref_substs_from_path(
+        &self,
         segment: PathSegment<'_>,
         resolved: TraitId,
-    ) -> Substs {
-        substs_from_path_segment(ctx, segment, Some(resolved.into()), false)
+        explicit_self_ty: Option<Ty>,
+    ) -> Substitution {
+        self.substs_from_path_segment(segment, Some(resolved.into()), false, explicit_self_ty)
     }
-}
 
-impl GenericPredicate {
-    pub(crate) fn from_where_predicate<'a>(
-        ctx: &'a TyLoweringContext<'a>,
+    pub(crate) fn lower_where_predicate(
+        &'a self,
         where_predicate: &'a WherePredicate,
-    ) -> impl Iterator<Item = GenericPredicate> + 'a {
+        ignore_bindings: bool,
+    ) -> impl Iterator<Item = QuantifiedWhereClause> + 'a {
         match where_predicate {
             WherePredicate::ForLifetime { target, bound, .. }
             | WherePredicate::TypeBound { target, bound } => {
                 let self_ty = match target {
-                    WherePredicateTypeTarget::TypeRef(type_ref) => Ty::from_hir(ctx, type_ref),
+                    WherePredicateTypeTarget::TypeRef(type_ref) => self.lower_ty(type_ref),
                     WherePredicateTypeTarget::TypeParam(param_id) => {
-                        let generic_def = ctx.resolver.generic_def().expect("generics in scope");
-                        let generics = generics(ctx.db.upcast(), generic_def);
+                        let generic_def = self.resolver.generic_def().expect("generics in scope");
+                        let generics = generics(self.db.upcast(), generic_def);
                         let param_id =
                             hir_def::TypeParamId { parent: generic_def, local_id: *param_id };
-                        let placeholder = to_placeholder_idx(ctx.db, param_id);
-                        match ctx.type_param_mode {
+                        let placeholder = to_placeholder_idx(self.db, param_id);
+                        match self.type_param_mode {
                             TypeParamLoweringMode::Placeholder => TyKind::Placeholder(placeholder),
                             TypeParamLoweringMode::Variable => {
                                 let idx = generics.param_idx(param_id).expect("matching generics");
@@ -704,7 +702,7 @@ pub(crate) fn from_where_predicate<'a>(
                         .intern(&Interner)
                     }
                 };
-                GenericPredicate::from_type_bound(ctx, bound, self_ty)
+                self.lower_type_bound(bound, self_ty, ignore_bindings)
                     .collect::<Vec<_>>()
                     .into_iter()
             }
@@ -712,87 +710,82 @@ pub(crate) fn from_where_predicate<'a>(
         }
     }
 
-    pub(crate) fn from_type_bound<'a>(
-        ctx: &'a TyLoweringContext<'a>,
+    pub(crate) fn lower_type_bound(
+        &'a self,
         bound: &'a TypeBound,
         self_ty: Ty,
-    ) -> impl Iterator<Item = GenericPredicate> + 'a {
+        ignore_bindings: bool,
+    ) -> impl Iterator<Item = QuantifiedWhereClause> + 'a {
         let mut bindings = None;
         let trait_ref = match bound {
             TypeBound::Path(path) => {
-                bindings = TraitRef::from_path(ctx, path, Some(self_ty));
-                Some(
-                    bindings.clone().map_or(GenericPredicate::Error, GenericPredicate::Implemented),
-                )
+                bindings = self.lower_trait_ref_from_path(path, Some(self_ty));
+                bindings.clone().map(WhereClause::Implemented).map(|b| Binders::wrap_empty(b))
             }
             TypeBound::Lifetime(_) => None,
-            TypeBound::Error => Some(GenericPredicate::Error),
+            TypeBound::Error => None,
         };
         trait_ref.into_iter().chain(
             bindings
                 .into_iter()
-                .flat_map(move |tr| assoc_type_bindings_from_type_bound(ctx, bound, tr)),
+                .filter(move |_| !ignore_bindings)
+                .flat_map(move |tr| self.assoc_type_bindings_from_type_bound(bound, tr)),
         )
     }
-}
 
-fn assoc_type_bindings_from_type_bound<'a>(
-    ctx: &'a TyLoweringContext<'a>,
-    bound: &'a TypeBound,
-    trait_ref: TraitRef,
-) -> impl Iterator<Item = GenericPredicate> + 'a {
-    let last_segment = match bound {
-        TypeBound::Path(path) => path.segments().last(),
-        TypeBound::Error | TypeBound::Lifetime(_) => None,
-    };
-    last_segment
-        .into_iter()
-        .flat_map(|segment| segment.args_and_bindings.into_iter())
-        .flat_map(|args_and_bindings| args_and_bindings.bindings.iter())
-        .flat_map(move |binding| {
-            let found = associated_type_by_name_including_super_traits(
-                ctx.db,
-                trait_ref.clone(),
-                &binding.name,
-            );
-            let (super_trait_ref, associated_ty) = match found {
-                None => return SmallVec::<[GenericPredicate; 1]>::new(),
-                Some(t) => t,
-            };
-            let projection_ty = ProjectionTy {
-                associated_ty: to_assoc_type_id(associated_ty),
-                parameters: super_trait_ref.substs,
-            };
-            let mut preds = SmallVec::with_capacity(
-                binding.type_ref.as_ref().map_or(0, |_| 1) + binding.bounds.len(),
-            );
-            if let Some(type_ref) = &binding.type_ref {
-                let ty = Ty::from_hir(ctx, type_ref);
-                let projection_predicate =
-                    ProjectionPredicate { projection_ty: projection_ty.clone(), ty };
-                preds.push(GenericPredicate::Projection(projection_predicate));
-            }
-            for bound in &binding.bounds {
-                preds.extend(GenericPredicate::from_type_bound(
-                    ctx,
-                    bound,
-                    TyKind::Alias(AliasTy::Projection(projection_ty.clone())).intern(&Interner),
-                ));
-            }
-            preds
-        })
-}
+    fn assoc_type_bindings_from_type_bound(
+        &'a self,
+        bound: &'a TypeBound,
+        trait_ref: TraitRef,
+    ) -> impl Iterator<Item = QuantifiedWhereClause> + 'a {
+        let last_segment = match bound {
+            TypeBound::Path(path) => path.segments().last(),
+            TypeBound::Error | TypeBound::Lifetime(_) => None,
+        };
+        last_segment
+            .into_iter()
+            .flat_map(|segment| segment.args_and_bindings.into_iter())
+            .flat_map(|args_and_bindings| args_and_bindings.bindings.iter())
+            .flat_map(move |binding| {
+                let found = associated_type_by_name_including_super_traits(
+                    self.db,
+                    trait_ref.clone(),
+                    &binding.name,
+                );
+                let (super_trait_ref, associated_ty) = match found {
+                    None => return SmallVec::<[QuantifiedWhereClause; 1]>::new(),
+                    Some(t) => t,
+                };
+                let projection_ty = ProjectionTy {
+                    associated_ty_id: to_assoc_type_id(associated_ty),
+                    substitution: super_trait_ref.substitution,
+                };
+                let mut preds = SmallVec::with_capacity(
+                    binding.type_ref.as_ref().map_or(0, |_| 1) + binding.bounds.len(),
+                );
+                if let Some(type_ref) = &binding.type_ref {
+                    let ty = self.lower_ty(type_ref);
+                    let alias_eq =
+                        AliasEq { alias: AliasTy::Projection(projection_ty.clone()), ty };
+                    preds.push(Binders::wrap_empty(WhereClause::AliasEq(alias_eq)));
+                }
+                for bound in &binding.bounds {
+                    preds.extend(self.lower_type_bound(
+                        bound,
+                        TyKind::Alias(AliasTy::Projection(projection_ty.clone())).intern(&Interner),
+                        false,
+                    ));
+                }
+                preds
+            })
+    }
 
-impl ReturnTypeImplTrait {
-    fn from_hir(ctx: &TyLoweringContext, bounds: &[TypeBound]) -> Self {
+    fn lower_impl_trait(&self, bounds: &[TypeBound]) -> ReturnTypeImplTrait {
         cov_mark::hit!(lower_rpit);
         let self_ty =
             TyKind::BoundVar(BoundVar::new(DebruijnIndex::INNERMOST, 0)).intern(&Interner);
-        let predicates = ctx.with_shifted_in(DebruijnIndex::ONE, |ctx| {
-            bounds
-                .iter()
-                .flat_map(|b| GenericPredicate::from_type_bound(ctx, b, self_ty.clone()))
-                .collect()
+        let predicates = self.with_shifted_in(DebruijnIndex::ONE, |ctx| {
+            bounds.iter().flat_map(|b| ctx.lower_type_bound(b, self_ty.clone(), false)).collect()
         });
         ReturnTypeImplTrait { bounds: Binders::new(1, predicates) }
     }
@@ -822,54 +815,54 @@ pub fn associated_type_shorthand_candidates<R>(
     res: TypeNs,
     mut cb: impl FnMut(&Name, &TraitRef, TypeAliasId) -> Option<R>,
 ) -> Option<R> {
-    let traits_from_env: Vec<_> = match res {
-        TypeNs::SelfType(impl_id) => match db.impl_trait(impl_id) {
-            None => vec![],
-            Some(trait_ref) => vec![trait_ref.value],
-        },
+    let mut search = |t| {
+        for t in all_super_trait_refs(db, t) {
+            let data = db.trait_data(t.hir_trait_id());
+
+            for (name, assoc_id) in &data.items {
+                if let AssocItemId::TypeAliasId(alias) = assoc_id {
+                    if let Some(result) = cb(name, &t, *alias) {
+                        return Some(result);
+                    }
+                }
+            }
+        }
+        None
+    };
+
+    match res {
+        // FIXME: how to correctly handle higher-ranked bounds here?
+        TypeNs::SelfType(impl_id) => {
+            search(db.impl_trait(impl_id)?.value.shift_bound_vars_out(DebruijnIndex::ONE))
+        }
         TypeNs::GenericParam(param_id) => {
             let predicates = db.generic_predicates_for_param(param_id);
-            let mut traits_: Vec<_> = predicates
-                .iter()
-                .filter_map(|pred| match &pred.value {
-                    GenericPredicate::Implemented(tr) => Some(tr.clone()),
-                    _ => None,
-                })
-                .collect();
+            let res = predicates.iter().find_map(|pred| match &pred.value.value {
+                // FIXME: how to correctly handle higher-ranked bounds here?
+                WhereClause::Implemented(tr) => {
+                    search(tr.clone().shift_bound_vars_out(DebruijnIndex::ONE))
+                }
+                _ => None,
+            });
+            if let res @ Some(_) = res {
+                return res;
+            }
             // Handle `Self::Type` referring to own associated type in trait definitions
             if let GenericDefId::TraitId(trait_id) = param_id.parent {
                 let generics = generics(db.upcast(), trait_id.into());
                 if generics.params.types[param_id.local_id].provenance
                     == TypeParamProvenance::TraitSelf
                 {
-                    let trait_ref = TraitRef {
-                        trait_: trait_id,
-                        substs: Substs::bound_vars(&generics, DebruijnIndex::INNERMOST),
-                    };
-                    traits_.push(trait_ref);
-                }
-            }
-            traits_
-        }
-        _ => vec![],
-    };
-
-    for t in traits_from_env.into_iter().flat_map(move |t| all_super_trait_refs(db, t)) {
-        let data = db.trait_data(t.trait_);
-
-        for (name, assoc_id) in &data.items {
-            match assoc_id {
-                AssocItemId::TypeAliasId(alias) => {
-                    if let Some(result) = cb(name, &t, *alias) {
-                        return Some(result);
-                    }
+                    let trait_ref = TyBuilder::trait_ref(db, trait_id)
+                        .fill_with_bound_vars(DebruijnIndex::INNERMOST, 0)
+                        .build();
+                    return search(trait_ref);
                 }
-                AssocItemId::FunctionId(_) | AssocItemId::ConstId(_) => {}
             }
+            None
         }
+        _ => None,
     }
-
-    None
 }
 
 /// Build the type of all specific fields of a struct or enum variant.
@@ -888,7 +881,7 @@ pub(crate) fn field_types_query(
     let ctx =
         TyLoweringContext::new(db, &resolver).with_type_param_mode(TypeParamLoweringMode::Variable);
     for (field_id, field_data) in var_data.fields().iter() {
-        res.insert(field_id, Binders::new(generics.len(), Ty::from_hir(&ctx, &field_data.type_ref)))
+        res.insert(field_id, Binders::new(generics.len(), ctx.lower_ty(&field_data.type_ref)))
     }
     Arc::new(res)
 }
@@ -904,7 +897,7 @@ pub(crate) fn field_types_query(
 pub(crate) fn generic_predicates_for_param_query(
     db: &dyn HirDatabase,
     param_id: TypeParamId,
-) -> Arc<[Binders<GenericPredicate>]> {
+) -> Arc<[Binders<QuantifiedWhereClause>]> {
     let resolver = param_id.parent.resolver(db.upcast());
     let ctx =
         TyLoweringContext::new(db, &resolver).with_type_param_mode(TypeParamLoweringMode::Variable);
@@ -916,15 +909,14 @@ pub(crate) fn generic_predicates_for_param_query(
             WherePredicate::ForLifetime { target, .. }
             | WherePredicate::TypeBound { target, .. } => match target {
                 WherePredicateTypeTarget::TypeRef(type_ref) => {
-                    Ty::from_hir_only_param(&ctx, type_ref) == Some(param_id)
+                    ctx.lower_ty_only_param(type_ref) == Some(param_id)
                 }
                 WherePredicateTypeTarget::TypeParam(local_id) => *local_id == param_id.local_id,
             },
             WherePredicate::Lifetime { .. } => false,
         })
         .flat_map(|pred| {
-            GenericPredicate::from_where_predicate(&ctx, pred)
-                .map(|p| Binders::new(generics.len(), p))
+            ctx.lower_where_predicate(pred, true).map(|p| Binders::new(generics.len(), p))
         })
         .collect()
 }
@@ -933,66 +925,62 @@ pub(crate) fn generic_predicates_for_param_recover(
     _db: &dyn HirDatabase,
     _cycle: &[String],
     _param_id: &TypeParamId,
-) -> Arc<[Binders<GenericPredicate>]> {
+) -> Arc<[Binders<QuantifiedWhereClause>]> {
     Arc::new([])
 }
 
-impl TraitEnvironment {
-    pub fn lower(db: &dyn HirDatabase, resolver: &Resolver) -> Arc<TraitEnvironment> {
-        let ctx = TyLoweringContext::new(db, &resolver)
-            .with_type_param_mode(TypeParamLoweringMode::Placeholder);
-        let mut traits_in_scope = Vec::new();
-        let mut clauses = Vec::new();
-        for pred in resolver.where_predicates_in_scope() {
-            for pred in GenericPredicate::from_where_predicate(&ctx, pred) {
-                if pred.is_error() {
-                    continue;
-                }
-                if let GenericPredicate::Implemented(tr) = &pred {
-                    traits_in_scope.push((tr.self_ty().clone(), tr.trait_));
-                }
-                let program_clause: chalk_ir::ProgramClause<Interner> =
-                    pred.clone().to_chalk(db).cast(&Interner);
-                clauses.push(program_clause.into_from_env_clause(&Interner));
+pub(crate) fn trait_environment_query(
+    db: &dyn HirDatabase,
+    def: GenericDefId,
+) -> Arc<TraitEnvironment> {
+    let resolver = def.resolver(db.upcast());
+    let ctx = TyLoweringContext::new(db, &resolver)
+        .with_type_param_mode(TypeParamLoweringMode::Placeholder);
+    let mut traits_in_scope = Vec::new();
+    let mut clauses = Vec::new();
+    for pred in resolver.where_predicates_in_scope() {
+        for pred in ctx.lower_where_predicate(pred, false) {
+            if let WhereClause::Implemented(tr) = &pred.skip_binders() {
+                traits_in_scope.push((tr.self_type_parameter().clone(), tr.hir_trait_id()));
             }
+            let program_clause: chalk_ir::ProgramClause<Interner> =
+                pred.clone().to_chalk(db).cast(&Interner);
+            clauses.push(program_clause.into_from_env_clause(&Interner));
         }
+    }
 
-        if let Some(def) = resolver.generic_def() {
-            let container: Option<AssocContainerId> = match def {
-                // FIXME: is there a function for this?
-                GenericDefId::FunctionId(f) => Some(f.lookup(db.upcast()).container),
-                GenericDefId::AdtId(_) => None,
-                GenericDefId::TraitId(_) => None,
-                GenericDefId::TypeAliasId(t) => Some(t.lookup(db.upcast()).container),
-                GenericDefId::ImplId(_) => None,
-                GenericDefId::EnumVariantId(_) => None,
-                GenericDefId::ConstId(c) => Some(c.lookup(db.upcast()).container),
-            };
-            if let Some(AssocContainerId::TraitId(trait_id)) = container {
-                // add `Self: Trait<T1, T2, ...>` to the environment in trait
-                // function default implementations (and hypothetical code
-                // inside consts or type aliases)
-                cov_mark::hit!(trait_self_implements_self);
-                let substs = Substs::type_params(db, trait_id);
-                let trait_ref = TraitRef { trait_: trait_id, substs };
-                let pred = GenericPredicate::Implemented(trait_ref);
-                let program_clause: chalk_ir::ProgramClause<Interner> =
-                    pred.clone().to_chalk(db).cast(&Interner);
-                clauses.push(program_clause.into_from_env_clause(&Interner));
-            }
-        }
+    let container: Option<AssocContainerId> = match def {
+        // FIXME: is there a function for this?
+        GenericDefId::FunctionId(f) => Some(f.lookup(db.upcast()).container),
+        GenericDefId::AdtId(_) => None,
+        GenericDefId::TraitId(_) => None,
+        GenericDefId::TypeAliasId(t) => Some(t.lookup(db.upcast()).container),
+        GenericDefId::ImplId(_) => None,
+        GenericDefId::EnumVariantId(_) => None,
+        GenericDefId::ConstId(c) => Some(c.lookup(db.upcast()).container),
+    };
+    if let Some(AssocContainerId::TraitId(trait_id)) = container {
+        // add `Self: Trait<T1, T2, ...>` to the environment in trait
+        // function default implementations (and hypothetical code
+        // inside consts or type aliases)
+        cov_mark::hit!(trait_self_implements_self);
+        let substs = TyBuilder::type_params_subst(db, trait_id);
+        let trait_ref = TraitRef { trait_id: to_chalk_trait_id(trait_id), substitution: substs };
+        let pred = WhereClause::Implemented(trait_ref);
+        let program_clause: chalk_ir::ProgramClause<Interner> = pred.to_chalk(db).cast(&Interner);
+        clauses.push(program_clause.into_from_env_clause(&Interner));
+    }
 
-        let env = chalk_ir::Environment::new(&Interner).add_clauses(&Interner, clauses);
+    let env = chalk_ir::Environment::new(&Interner).add_clauses(&Interner, clauses);
 
-        Arc::new(TraitEnvironment { traits_from_clauses: traits_in_scope, env })
-    }
+    Arc::new(TraitEnvironment { traits_from_clauses: traits_in_scope, env })
 }
 
 /// Resolve the where clause(s) of an item with generics.
 pub(crate) fn generic_predicates_query(
     db: &dyn HirDatabase,
     def: GenericDefId,
-) -> Arc<[Binders<GenericPredicate>]> {
+) -> Arc<[Binders<QuantifiedWhereClause>]> {
     let resolver = def.resolver(db.upcast());
     let ctx =
         TyLoweringContext::new(db, &resolver).with_type_param_mode(TypeParamLoweringMode::Variable);
@@ -1000,8 +988,7 @@ pub(crate) fn generic_predicates_query(
     resolver
         .where_predicates_in_scope()
         .flat_map(|pred| {
-            GenericPredicate::from_where_predicate(&ctx, pred)
-                .map(|p| Binders::new(generics.len(), p))
+            ctx.lower_where_predicate(pred, false).map(|p| Binders::new(generics.len(), p))
         })
         .collect()
 }
@@ -1020,20 +1007,18 @@ pub(crate) fn generic_defaults_query(
         .iter()
         .enumerate()
         .map(|(idx, (_, p))| {
-            let mut ty = p
-                .default
-                .as_ref()
-                .map_or(TyKind::Unknown.intern(&Interner), |t| Ty::from_hir(&ctx, t));
+            let mut ty =
+                p.default.as_ref().map_or(TyKind::Error.intern(&Interner), |t| ctx.lower_ty(t));
 
             // Each default can only refer to previous parameters.
             ty.walk_mut_binders(
-                &mut |ty, binders| match &mut ty.0 {
+                &mut |ty, binders| match ty.interned_mut() {
                     TyKind::BoundVar(BoundVar { debruijn, index }) if *debruijn == binders => {
                         if *index >= idx {
                             // type variable default referring to parameter coming
                             // after it. This is forbidden (FIXME: report
                             // diagnostic)
-                            *ty = TyKind::Unknown.intern(&Interner);
+                            *ty = TyKind::Error.intern(&Interner);
                         }
                     }
                     _ => {}
@@ -1054,23 +1039,23 @@ fn fn_sig_for_fn(db: &dyn HirDatabase, def: FunctionId) -> PolyFnSig {
     let ctx_params = TyLoweringContext::new(db, &resolver)
         .with_impl_trait_mode(ImplTraitLoweringMode::Variable)
         .with_type_param_mode(TypeParamLoweringMode::Variable);
-    let params = data.params.iter().map(|tr| Ty::from_hir(&ctx_params, tr)).collect::<Vec<_>>();
+    let params = data.params.iter().map(|tr| (&ctx_params).lower_ty(tr)).collect::<Vec<_>>();
     let ctx_ret = TyLoweringContext::new(db, &resolver)
         .with_impl_trait_mode(ImplTraitLoweringMode::Opaque)
         .with_type_param_mode(TypeParamLoweringMode::Variable);
-    let ret = Ty::from_hir(&ctx_ret, &data.ret_type);
+    let ret = (&ctx_ret).lower_ty(&data.ret_type);
     let generics = generics(db.upcast(), def.into());
     let num_binders = generics.len();
-    Binders::new(num_binders, CallableSig::from_params_and_return(params, ret, data.is_varargs))
+    Binders::new(num_binders, CallableSig::from_params_and_return(params, ret, data.is_varargs()))
 }
 
 /// Build the declared type of a function. This should not need to look at the
 /// function body.
 fn type_for_fn(db: &dyn HirDatabase, def: FunctionId) -> Binders<Ty> {
     let generics = generics(db.upcast(), def.into());
-    let substs = Substs::bound_vars(&generics, DebruijnIndex::INNERMOST);
+    let substs = generics.bound_vars_subst(DebruijnIndex::INNERMOST);
     Binders::new(
-        substs.len(),
+        substs.len(&Interner),
         TyKind::FnDef(CallableDefId::FunctionId(def).to_chalk(db), substs).intern(&Interner),
     )
 }
@@ -1083,7 +1068,7 @@ fn type_for_const(db: &dyn HirDatabase, def: ConstId) -> Binders<Ty> {
     let ctx =
         TyLoweringContext::new(db, &resolver).with_type_param_mode(TypeParamLoweringMode::Variable);
 
-    Binders::new(generics.len(), Ty::from_hir(&ctx, &data.type_ref))
+    Binders::new(generics.len(), ctx.lower_ty(&data.type_ref))
 }
 
 /// Build the declared type of a static.
@@ -1092,7 +1077,7 @@ fn type_for_static(db: &dyn HirDatabase, def: StaticId) -> Binders<Ty> {
     let resolver = def.resolver(db.upcast());
     let ctx = TyLoweringContext::new(db, &resolver);
 
-    Binders::new(0, Ty::from_hir(&ctx, &data.type_ref))
+    Binders::new(0, ctx.lower_ty(&data.type_ref))
 }
 
 fn fn_sig_for_struct_constructor(db: &dyn HirDatabase, def: StructId) -> PolyFnSig {
@@ -1101,8 +1086,7 @@ fn fn_sig_for_struct_constructor(db: &dyn HirDatabase, def: StructId) -> PolyFnS
     let resolver = def.resolver(db.upcast());
     let ctx =
         TyLoweringContext::new(db, &resolver).with_type_param_mode(TypeParamLoweringMode::Variable);
-    let params =
-        fields.iter().map(|(_, field)| Ty::from_hir(&ctx, &field.type_ref)).collect::<Vec<_>>();
+    let params = fields.iter().map(|(_, field)| ctx.lower_ty(&field.type_ref)).collect::<Vec<_>>();
     let ret = type_for_adt(db, def.into());
     Binders::new(ret.num_binders, CallableSig::from_params_and_return(params, ret.value, false))
 }
@@ -1114,9 +1098,9 @@ fn type_for_struct_constructor(db: &dyn HirDatabase, def: StructId) -> Binders<T
         return type_for_adt(db, def.into());
     }
     let generics = generics(db.upcast(), def.into());
-    let substs = Substs::bound_vars(&generics, DebruijnIndex::INNERMOST);
+    let substs = generics.bound_vars_subst(DebruijnIndex::INNERMOST);
     Binders::new(
-        substs.len(),
+        substs.len(&Interner),
         TyKind::FnDef(CallableDefId::StructId(def).to_chalk(db), substs).intern(&Interner),
     )
 }
@@ -1128,8 +1112,7 @@ fn fn_sig_for_enum_variant_constructor(db: &dyn HirDatabase, def: EnumVariantId)
     let resolver = def.parent.resolver(db.upcast());
     let ctx =
         TyLoweringContext::new(db, &resolver).with_type_param_mode(TypeParamLoweringMode::Variable);
-    let params =
-        fields.iter().map(|(_, field)| Ty::from_hir(&ctx, &field.type_ref)).collect::<Vec<_>>();
+    let params = fields.iter().map(|(_, field)| ctx.lower_ty(&field.type_ref)).collect::<Vec<_>>();
     let ret = type_for_adt(db, def.parent.into());
     Binders::new(ret.num_binders, CallableSig::from_params_and_return(params, ret.value, false))
 }
@@ -1142,17 +1125,18 @@ fn type_for_enum_variant_constructor(db: &dyn HirDatabase, def: EnumVariantId) -
         return type_for_adt(db, def.parent.into());
     }
     let generics = generics(db.upcast(), def.parent.into());
-    let substs = Substs::bound_vars(&generics, DebruijnIndex::INNERMOST);
+    let substs = generics.bound_vars_subst(DebruijnIndex::INNERMOST);
     Binders::new(
-        substs.len(),
+        substs.len(&Interner),
         TyKind::FnDef(CallableDefId::EnumVariantId(def).to_chalk(db), substs).intern(&Interner),
     )
 }
 
 fn type_for_adt(db: &dyn HirDatabase, adt: AdtId) -> Binders<Ty> {
-    let generics = generics(db.upcast(), adt.into());
-    let substs = Substs::bound_vars(&generics, DebruijnIndex::INNERMOST);
-    Binders::new(substs.len(), Ty::adt_ty(adt, substs))
+    let b = TyBuilder::adt(db, adt);
+    let num_binders = b.remaining();
+    let ty = b.fill_with_bound_vars(DebruijnIndex::INNERMOST, 0).build();
+    Binders::new(num_binders, ty)
 }
 
 fn type_for_type_alias(db: &dyn HirDatabase, t: TypeAliasId) -> Binders<Ty> {
@@ -1161,12 +1145,11 @@ fn type_for_type_alias(db: &dyn HirDatabase, t: TypeAliasId) -> Binders<Ty> {
     let ctx =
         TyLoweringContext::new(db, &resolver).with_type_param_mode(TypeParamLoweringMode::Variable);
     if db.type_alias_data(t).is_extern {
-        Binders::new(0, TyKind::ForeignType(crate::to_foreign_def_id(t)).intern(&Interner))
+        Binders::new(0, TyKind::Foreign(crate::to_foreign_def_id(t)).intern(&Interner))
     } else {
-        let substs = Substs::bound_vars(&generics, DebruijnIndex::INNERMOST);
         let type_ref = &db.type_alias_data(t).type_ref;
-        let inner = Ty::from_hir(&ctx, type_ref.as_ref().unwrap_or(&TypeRef::Error));
-        Binders::new(substs.len(), inner)
+        let inner = ctx.lower_ty(type_ref.as_deref().unwrap_or(&TypeRef::Error));
+        Binders::new(generics.len(), inner)
     }
 }
 
@@ -1225,7 +1208,7 @@ pub enum ValueTyDefId {
 /// namespace.
 pub(crate) fn ty_query(db: &dyn HirDatabase, def: TyDefId) -> Binders<Ty> {
     match def {
-        TyDefId::BuiltinType(it) => Binders::new(0, Ty::builtin(it)),
+        TyDefId::BuiltinType(it) => Binders::new(0, TyBuilder::builtin(it)),
         TyDefId::AdtId(it) => type_for_adt(db, it),
         TyDefId::TypeAliasId(it) => type_for_type_alias(db, it),
     }
@@ -1237,7 +1220,7 @@ pub(crate) fn ty_recover(db: &dyn HirDatabase, _cycle: &[String], def: &TyDefId)
         TyDefId::AdtId(it) => generics(db.upcast(), it.into()).len(),
         TyDefId::TypeAliasId(it) => generics(db.upcast(), it.into()).len(),
     };
-    Binders::new(num_binders, TyKind::Unknown.intern(&Interner))
+    Binders::new(num_binders, TyKind::Error.intern(&Interner))
 }
 
 pub(crate) fn value_ty_query(db: &dyn HirDatabase, def: ValueTyDefId) -> Binders<Ty> {
@@ -1257,7 +1240,7 @@ pub(crate) fn impl_self_ty_query(db: &dyn HirDatabase, impl_id: ImplId) -> Binde
     let generics = generics(db.upcast(), impl_id.into());
     let ctx =
         TyLoweringContext::new(db, &resolver).with_type_param_mode(TypeParamLoweringMode::Variable);
-    Binders::new(generics.len(), Ty::from_hir(&ctx, &impl_data.target_type))
+    Binders::new(generics.len(), ctx.lower_ty(&impl_data.self_ty))
 }
 
 pub(crate) fn const_param_ty_query(db: &dyn HirDatabase, def: ConstParamId) -> Ty {
@@ -1266,7 +1249,7 @@ pub(crate) fn const_param_ty_query(db: &dyn HirDatabase, def: ConstParamId) -> T
     let resolver = def.parent.resolver(db.upcast());
     let ctx = TyLoweringContext::new(db, &resolver);
 
-    Ty::from_hir(&ctx, &data.ty)
+    ctx.lower_ty(&data.ty)
 }
 
 pub(crate) fn impl_self_ty_recover(
@@ -1275,7 +1258,7 @@ pub(crate) fn impl_self_ty_recover(
     impl_id: &ImplId,
 ) -> Binders<Ty> {
     let generics = generics(db.upcast(), (*impl_id).into());
-    Binders::new(generics.len(), TyKind::Unknown.intern(&Interner))
+    Binders::new(generics.len(), TyKind::Error.intern(&Interner))
 }
 
 pub(crate) fn impl_trait_query(db: &dyn HirDatabase, impl_id: ImplId) -> Option<Binders<TraitRef>> {
@@ -1285,10 +1268,7 @@ pub(crate) fn impl_trait_query(db: &dyn HirDatabase, impl_id: ImplId) -> Option<
         TyLoweringContext::new(db, &resolver).with_type_param_mode(TypeParamLoweringMode::Variable);
     let self_ty = db.impl_self_ty(impl_id);
     let target_trait = impl_data.target_trait.as_ref()?;
-    Some(Binders::new(
-        self_ty.num_binders,
-        TraitRef::from_hir(&ctx, target_trait, Some(self_ty.value))?,
-    ))
+    Some(Binders::new(self_ty.num_binders, ctx.lower_trait_ref(target_trait, Some(self_ty.value))?))
 }
 
 pub(crate) fn return_type_impl_traits(
@@ -1301,7 +1281,7 @@ pub(crate) fn return_type_impl_traits(
     let ctx_ret = TyLoweringContext::new(db, &resolver)
         .with_impl_trait_mode(ImplTraitLoweringMode::Opaque)
         .with_type_param_mode(TypeParamLoweringMode::Variable);
-    let _ret = Ty::from_hir(&ctx_ret, &data.ret_type);
+    let _ret = (&ctx_ret).lower_ty(&data.ret_type);
     let generics = generics(db.upcast(), def.into());
     let num_binders = generics.len();
     let return_type_impl_traits =