11 files changed, 136 insertions, 127 deletions

diff --git a/crates/ra_hir_ty/src/db.rs b/crates/ra_hir_ty/src/db.rs
index fea122a8b..7684ade06 100644
--- a/crates/ra_hir_ty/src/db.rs
+++ b/crates/ra_hir_ty/src/db.rs
@@ -3,10 +3,10 @@
 use std::sync::Arc;
 
 use hir_def::{
-    db::DefDatabase, DefWithBodyId, GenericDefId, ImplId, LocalStructFieldId, TraitId, VariantId,
+    db::DefDatabase, DefWithBodyId, GenericDefId, ImplId, LocalStructFieldId, TraitId, VariantId, TypeParamId,
 };
 use ra_arena::map::ArenaMap;
-use ra_db::{salsa, CrateId};
+use ra_db::{impl_intern_key, salsa, CrateId};
 use ra_prof::profile;
 
 use crate::{
@@ -37,10 +37,10 @@ pub trait HirDatabase: DefDatabase {
     fn impl_self_ty(&self, def: ImplId) -> Binders<Ty>;
 
     #[salsa::invoke(crate::lower::impl_trait_query)]
-    fn impl_trait(&self, def: ImplId) -> Option<TraitRef>;
+    fn impl_trait(&self, def: ImplId) -> Option<Binders<TraitRef>>;
 
     #[salsa::invoke(crate::lower::field_types_query)]
-    fn field_types(&self, var: VariantId) -> Arc<ArenaMap<LocalStructFieldId, Ty>>;
+    fn field_types(&self, var: VariantId) -> Arc<ArenaMap<LocalStructFieldId, Binders<Ty>>>;
 
     #[salsa::invoke(crate::callable_item_sig)]
     fn callable_item_signature(&self, def: CallableDef) -> PolyFnSig;
@@ -49,8 +49,7 @@ pub trait HirDatabase: DefDatabase {
     #[salsa::cycle(crate::lower::generic_predicates_for_param_recover)]
     fn generic_predicates_for_param(
         &self,
-        def: GenericDefId,
-        param_idx: u32,
+        param_id: TypeParamId,
     ) -> Arc<[GenericPredicate]>;
 
     #[salsa::invoke(crate::lower::generic_predicates_query)]
@@ -77,6 +76,8 @@ pub trait HirDatabase: DefDatabase {
     #[salsa::interned]
     fn intern_type_ctor(&self, type_ctor: TypeCtor) -> crate::TypeCtorId;
     #[salsa::interned]
+    fn intern_type_param_id(&self, param_id: TypeParamId) -> GlobalTypeParamId;
+    #[salsa::interned]
     fn intern_chalk_impl(&self, impl_: Impl) -> crate::traits::GlobalImplId;
     #[salsa::interned]
     fn intern_assoc_ty_value(&self, assoc_ty_value: AssocTyValue) -> crate::traits::AssocTyValueId;
@@ -117,3 +118,7 @@ fn infer(db: &impl HirDatabase, def: DefWithBodyId) -> Arc<InferenceResult> {
 fn hir_database_is_object_safe() {
     fn _assert_object_safe(_: &dyn HirDatabase) {}
 }
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
+pub struct GlobalTypeParamId(salsa::InternId);
+impl_intern_key!(GlobalTypeParamId);
diff --git a/crates/ra_hir_ty/src/infer/coerce.rs b/crates/ra_hir_ty/src/infer/coerce.rs
index 83c0c2c3f..2a9567898 100644
--- a/crates/ra_hir_ty/src/infer/coerce.rs
+++ b/crates/ra_hir_ty/src/infer/coerce.rs
@@ -57,8 +57,8 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
                 let trait_ref = db.impl_trait(impl_id)?;
 
                 // `CoerseUnsized` has one generic parameter for the target type.
-                let cur_from_ty = trait_ref.substs.0.get(0)?;
-                let cur_to_ty = trait_ref.substs.0.get(1)?;
+                let cur_from_ty = trait_ref.value.substs.0.get(0)?;
+                let cur_to_ty = trait_ref.value.substs.0.get(1)?;
 
                 match (&cur_from_ty, cur_to_ty) {
                     (ty_app!(ctor1, st1), ty_app!(ctor2, st2)) => {
@@ -66,8 +66,8 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
                         // This works for smart-pointer-like coercion, which covers all impls from std.
                         st1.iter().zip(st2.iter()).enumerate().find_map(|(i, (ty1, ty2))| {
                             match (ty1, ty2) {
-                                (Ty::Param { idx: p1, .. }, Ty::Param { idx: p2, .. })
-                                    if p1 != p2 =>
+                                (Ty::Bound(idx1), Ty::Bound(idx2))
+                                    if idx1 != idx2 =>
                                 {
                                     Some(((*ctor1, *ctor2), i))
                                 }
@@ -256,8 +256,8 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
                 let unsize_generic_index = {
                     let mut index = None;
                     let mut multiple_param = false;
-                    field_tys[last_field_id].walk(&mut |ty| match ty {
-                        &Ty::Param { idx, .. } => {
+                    field_tys[last_field_id].value.walk(&mut |ty| match ty {
+                        &Ty::Bound(idx) => {
                             if index.is_none() {
                                 index = Some(idx);
                             } else if Some(idx) != index {
@@ -276,8 +276,8 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
                 // Check other fields do not involve it.
                 let mut multiple_used = false;
                 fields.for_each(|(field_id, _data)| {
-                    field_tys[field_id].walk(&mut |ty| match ty {
-                        &Ty::Param { idx, .. } if idx == unsize_generic_index => {
+                    field_tys[field_id].value.walk(&mut |ty| match ty {
+                        &Ty::Bound(idx) if idx == unsize_generic_index => {
                             multiple_used = true
                         }
                         _ => {}
diff --git a/crates/ra_hir_ty/src/infer/expr.rs b/crates/ra_hir_ty/src/infer/expr.rs
index e1fdb356d..8b8378499 100644
--- a/crates/ra_hir_ty/src/infer/expr.rs
+++ b/crates/ra_hir_ty/src/infer/expr.rs
@@ -236,8 +236,7 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
                         self.result.record_field_resolutions.insert(field.expr, field_def);
                     }
                     let field_ty = field_def
-                        .map_or(Ty::Unknown, |it| field_types[it.local_id].clone())
-                        .subst(&substs);
+                        .map_or(Ty::Unknown, |it| field_types[it.local_id].clone().subst(&substs));
                     self.infer_expr_coerce(field.expr, &Expectation::has_type(field_ty));
                 }
                 if let Some(expr) = spread {
@@ -686,7 +685,7 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
             if let TypeCtor::FnDef(def) = a_ty.ctor {
                 let generic_predicates = self.db.generic_predicates(def.into());
                 for predicate in generic_predicates.iter() {
-                    let predicate = predicate.clone().subst(&a_ty.parameters);
+                    let predicate = predicate.clone().subst_type_params(self.db, def.into(), &a_ty.parameters);
                     if let Some(obligation) = Obligation::from_predicate(predicate) {
                         self.obligations.push(obligation);
                     }
diff --git a/crates/ra_hir_ty/src/infer/pat.rs b/crates/ra_hir_ty/src/infer/pat.rs
index a14662884..e7283f24c 100644
--- a/crates/ra_hir_ty/src/infer/pat.rs
+++ b/crates/ra_hir_ty/src/infer/pat.rs
@@ -12,7 +12,7 @@ use hir_expand::name::Name;
 use test_utils::tested_by;
 
 use super::{BindingMode, InferenceContext};
-use crate::{db::HirDatabase, utils::variant_data, Substs, Ty, TypeCtor, TypeWalk};
+use crate::{db::HirDatabase, utils::variant_data, Substs, Ty, TypeCtor};
 
 impl<'a, D: HirDatabase> InferenceContext<'a, D> {
     fn infer_tuple_struct_pat(
@@ -34,8 +34,7 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
             let expected_ty = var_data
                 .as_ref()
                 .and_then(|d| d.field(&Name::new_tuple_field(i)))
-                .map_or(Ty::Unknown, |field| field_tys[field].clone())
-                .subst(&substs);
+                .map_or(Ty::Unknown, |field| field_tys[field].clone().subst(&substs));
             let expected_ty = self.normalize_associated_types_in(expected_ty);
             self.infer_pat(subpat, &expected_ty, default_bm);
         }
@@ -65,7 +64,7 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
         for subpat in subpats {
             let matching_field = var_data.as_ref().and_then(|it| it.field(&subpat.name));
             let expected_ty =
-                matching_field.map_or(Ty::Unknown, |field| field_tys[field].clone()).subst(&substs);
+                matching_field.map_or(Ty::Unknown, |field| field_tys[field].clone().subst(&substs));
             let expected_ty = self.normalize_associated_types_in(expected_ty);
             self.infer_pat(subpat.pat, &expected_ty, default_bm);
         }
diff --git a/crates/ra_hir_ty/src/lib.rs b/crates/ra_hir_ty/src/lib.rs
index 1f0fd1128..1e162943c 100644
--- a/crates/ra_hir_ty/src/lib.rs
+++ b/crates/ra_hir_ty/src/lib.rs
@@ -45,10 +45,10 @@ use std::{fmt, iter, mem};
 
 use hir_def::{
     expr::ExprId, type_ref::Mutability, AdtId, AssocContainerId, DefWithBodyId, GenericDefId,
-    HasModule, Lookup, TraitId, TypeAliasId,
+    HasModule, Lookup, TraitId, TypeAliasId, TypeParamId, generics::TypeParamProvenance,
 };
-use hir_expand::name::Name;
 use ra_db::{impl_intern_key, salsa, CrateId};
+use hir_expand::name::Name;
 
 use crate::{
     db::HirDatabase,
@@ -288,14 +288,7 @@ pub enum Ty {
     Projection(ProjectionTy),
 
     /// A type parameter; for example, `T` in `fn f<T>(x: T) {}
-    Param {
-        /// The index of the parameter (starting with parameters from the
-        /// surrounding impl, then the current function).
-        idx: u32,
-        /// The name of the parameter, for displaying.
-        // FIXME get rid of this
-        name: Name,
-    },
+    Param(TypeParamId),
 
     /// A bound type variable. Used during trait resolution to represent Chalk
     /// variables, and in `Dyn` and `Opaque` bounds to represent the `Self` type.
@@ -366,15 +359,15 @@ impl Substs {
     }
 
     /// Return Substs that replace each parameter by itself (i.e. `Ty::Param`).
-    pub(crate) fn identity(generic_params: &Generics) -> Substs {
+    pub(crate) fn type_params(generic_params: &Generics) -> Substs {
         Substs(
-            generic_params.iter().map(|(idx, p)| Ty::Param { idx, name: p.name.clone().unwrap_or_else(Name::missing) }).collect(),
+            generic_params.iter().map(|(id, _)| Ty::Param(id)).collect(),
         )
     }
 
     /// Return Substs that replace each parameter by a bound variable.
     pub(crate) fn bound_vars(generic_params: &Generics) -> Substs {
-        Substs(generic_params.iter().map(|(idx, _p)| Ty::Bound(idx)).collect())
+        Substs(generic_params.iter().enumerate().map(|(idx, _)| Ty::Bound(idx as u32)).collect())
     }
 
     pub fn build_for_def(db: &impl HirDatabase, def: impl Into<GenericDefId>) -> SubstsBuilder {
@@ -422,11 +415,6 @@ impl SubstsBuilder {
         self.fill((starting_from..).map(Ty::Bound))
     }
 
-    pub fn fill_with_params(self) -> Self {
-        let start = self.vec.len() as u32;
-        self.fill((start..).map(|idx| Ty::Param { idx, name: Name::missing() }))
-    }
-
     pub fn fill_with_unknown(self) -> Self {
         self.fill(iter::repeat(Ty::Unknown))
     }
@@ -762,13 +750,19 @@ pub trait TypeWalk {
     /// Replaces type parameters in this type using the given `Substs`. (So e.g.
     /// if `self` is `&[T]`, where type parameter T has index 0, and the
     /// `Substs` contain `u32` at index 0, we'll have `&[u32]` afterwards.)
-    fn subst(self, substs: &Substs) -> Self
+    // TODO: this should mostly not be used anymore
+    fn subst_type_params(self, db: &impl HirDatabase, def: GenericDefId, substs: &Substs) -> Self
     where
         Self: Sized,
     {
+        let generics = generics(db, def);
         self.fold(&mut |ty| match ty {
-            Ty::Param { idx, name } => {
-                substs.get(idx as usize).cloned().unwrap_or(Ty::Param { idx, name })
+            Ty::Param(id) => {
+                if let Some(idx) = generics.param_idx(id) {
+                    substs.get(idx as usize).cloned().unwrap_or(Ty::Param(id))
+                } else {
+                    ty
+                }
             }
             ty => ty,
         })
@@ -1042,7 +1036,18 @@ impl HirDisplay for Ty {
         match self {
             Ty::Apply(a_ty) => a_ty.hir_fmt(f)?,
             Ty::Projection(p_ty) => p_ty.hir_fmt(f)?,
-            Ty::Param { name, .. } => write!(f, "{}", name)?,
+            Ty::Param(id) => {
+                let generic_params = f.db.generic_params(id.parent);
+                let param_data = &generic_params.types[id.local_id];
+                match param_data.provenance {
+                    TypeParamProvenance::TypeParamList | TypeParamProvenance::TraitSelf => {
+                        write!(f, "{}", param_data.name.clone().unwrap_or_else(Name::missing))?
+                    }
+                    TypeParamProvenance::ArgumentImplTrait => {
+                        write!(f, "impl TODO")?
+                    }
+                }
+            },
             Ty::Bound(idx) => write!(f, "?{}", idx)?,
             Ty::Dyn(predicates) | Ty::Opaque(predicates) => {
                 match self {
diff --git a/crates/ra_hir_ty/src/lower.rs b/crates/ra_hir_ty/src/lower.rs
index 88d962b47..d60b59433 100644
--- a/crates/ra_hir_ty/src/lower.rs
+++ b/crates/ra_hir_ty/src/lower.rs
@@ -30,7 +30,7 @@ use crate::{
     Binders, FnSig, GenericPredicate, PolyFnSig, ProjectionPredicate, ProjectionTy, Substs,
     TraitEnvironment, TraitRef, Ty, TypeCtor,
 };
-use hir_expand::name::Name;
+use hir_def::TypeParamId;
 
 #[derive(Debug)]
 pub struct TyLoweringContext<'a, DB: HirDatabase> {
@@ -145,7 +145,16 @@ impl Ty {
                     ImplTraitLoweringMode::Param => {
                         let idx = ctx.impl_trait_counter.get();
                         ctx.impl_trait_counter.set(idx + 1);
-                        Ty::Param { idx: idx as u32, name: Name::missing() }
+                        if let Some(def) = ctx.resolver.generic_def() {
+                            let generics = generics(ctx.db, def);
+                            let param = generics
+                                .iter()
+                                .nth(idx as usize)
+                                .map_or(Ty::Unknown, |(id, _)| Ty::Param(id));
+                            param
+                        } else {
+                            Ty::Unknown
+                        }
                     }
                     ImplTraitLoweringMode::Variable => {
                         let idx = ctx.impl_trait_counter.get();
@@ -176,7 +185,7 @@ impl Ty {
     fn from_hir_only_param(
         ctx: &TyLoweringContext<'_, impl HirDatabase>,
         type_ref: &TypeRef,
-    ) -> Option<u32> {
+    ) -> Option<TypeParamId> {
         let path = match type_ref {
             TypeRef::Path(path) => path,
             _ => return None,
@@ -192,9 +201,7 @@ impl Ty {
             _ => return None,
         };
         if let TypeNs::GenericParam(param_id) = resolution {
-            let generics = generics(ctx.db, ctx.resolver.generic_def().expect("generics in scope"));
-            let idx = generics.param_idx(param_id);
-            Some(idx)
+            Some(param_id)
         } else {
             None
         }
@@ -256,20 +263,18 @@ impl Ty {
             TypeNs::GenericParam(param_id) => {
                 let generics =
                     generics(ctx.db, ctx.resolver.generic_def().expect("generics in scope"));
-                let idx = generics.param_idx(param_id);
                 match ctx.type_param_mode {
-                    TypeParamLoweringMode::Placeholder => {
-                        // FIXME: maybe return name in resolution?
-                        let name = generics.param_name(param_id);
-                        Ty::Param { idx, name }
+                    TypeParamLoweringMode::Placeholder => Ty::Param(param_id),
+                    TypeParamLoweringMode::Variable => {
+                        let idx = generics.param_idx(param_id).expect("matching generics");
+                        Ty::Bound(idx)
                     }
-                    TypeParamLoweringMode::Variable => Ty::Bound(idx),
                 }
             }
             TypeNs::SelfType(impl_id) => {
                 let generics = generics(ctx.db, impl_id.into());
                 let substs = match ctx.type_param_mode {
-                    TypeParamLoweringMode::Placeholder => Substs::identity(&generics),
+                    TypeParamLoweringMode::Placeholder => Substs::type_params(&generics),
                     TypeParamLoweringMode::Variable => Substs::bound_vars(&generics),
                 };
                 ctx.db.impl_self_ty(impl_id).subst(&substs)
@@ -277,7 +282,7 @@ impl Ty {
             TypeNs::AdtSelfType(adt) => {
                 let generics = generics(ctx.db, adt.into());
                 let substs = match ctx.type_param_mode {
-                    TypeParamLoweringMode::Placeholder => Substs::identity(&generics),
+                    TypeParamLoweringMode::Placeholder => Substs::type_params(&generics),
                     TypeParamLoweringMode::Variable => Substs::bound_vars(&generics),
                 };
                 ctx.db.ty(adt.into()).subst(&substs)
@@ -319,20 +324,28 @@ impl Ty {
         self_ty: Ty,
         segment: PathSegment<'_>,
     ) -> Ty {
-        let param_idx = match self_ty {
-            Ty::Param { idx, .. } if ctx.type_param_mode == TypeParamLoweringMode::Placeholder => idx,
-            Ty::Bound(idx) if ctx.type_param_mode == TypeParamLoweringMode::Variable => idx,
-            _ => return Ty::Unknown, // Error: Ambiguous associated type
-        };
         let def = match ctx.resolver.generic_def() {
             Some(def) => def,
             None => return Ty::Unknown, // this can't actually happen
         };
-        let predicates = ctx.db.generic_predicates_for_param(def.into(), param_idx);
+        let param_id = match self_ty {
+            Ty::Param(id) if ctx.type_param_mode == TypeParamLoweringMode::Placeholder => id,
+            Ty::Bound(idx) if ctx.type_param_mode == TypeParamLoweringMode::Variable => {
+                let generics = generics(ctx.db, def);
+                let param_id = if let Some((id, _)) = generics.iter().nth(idx as usize) {
+                    id
+                } else {
+                    return Ty::Unknown;
+                };
+                param_id
+            },
+            _ => return Ty::Unknown, // Error: Ambiguous associated type
+        };
+        let predicates = ctx.db.generic_predicates_for_param(param_id);
         let traits_from_env = predicates.iter().filter_map(|pred| match pred {
             GenericPredicate::Implemented(tr) => {
-                if let Ty::Param { idx, .. } = tr.self_ty() {
-                    if *idx == param_idx {
+                if let Ty::Param(id) = tr.self_ty() {
+                    if *id == param_id {
                         return Some(tr.trait_);
                     }
                 }
@@ -530,13 +543,12 @@ impl GenericPredicate {
                 let generic_def = ctx.resolver.generic_def().expect("generics in scope");
                 let generics = generics(ctx.db, generic_def);
                 let param_id = hir_def::TypeParamId { parent: generic_def, local_id: *param_id };
-                let idx = generics.param_idx(param_id);
                 match ctx.type_param_mode {
-                    TypeParamLoweringMode::Placeholder => {
-                        let name = generics.param_name(param_id);
-                        Ty::Param { idx, name }
+                    TypeParamLoweringMode::Placeholder => Ty::Param(param_id),
+                    TypeParamLoweringMode::Variable => {
+                        let idx = generics.param_idx(param_id).expect("matching generics");
+                        Ty::Bound(idx)
                     }
-                    TypeParamLoweringMode::Variable => Ty::Bound(idx),
                 }
             }
         };
@@ -599,17 +611,19 @@ pub fn callable_item_sig(db: &impl HirDatabase, def: CallableDef) -> PolyFnSig {
 pub(crate) fn field_types_query(
     db: &impl HirDatabase,
     variant_id: VariantId,
-) -> Arc<ArenaMap<LocalStructFieldId, Ty>> {
+) -> Arc<ArenaMap<LocalStructFieldId, Binders<Ty>>> {
     let var_data = variant_data(db, variant_id);
-    let resolver = match variant_id {
-        VariantId::StructId(it) => it.resolver(db),
-        VariantId::UnionId(it) => it.resolver(db),
-        VariantId::EnumVariantId(it) => it.parent.resolver(db),
+    let (resolver, def): (_, GenericDefId) = match variant_id {
+        VariantId::StructId(it) => (it.resolver(db), it.into()),
+        VariantId::UnionId(it) => (it.resolver(db), it.into()),
+        VariantId::EnumVariantId(it) => (it.parent.resolver(db), it.parent.into()),
     };
+    let generics = generics(db, def);
     let mut res = ArenaMap::default();
-    let ctx = TyLoweringContext::new(db, &resolver);
+    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, Ty::from_hir(&ctx, &field_data.type_ref))
+        res.insert(field_id, Binders::new(generics.len(), Ty::from_hir(&ctx, &field_data.type_ref)))
     }
     Arc::new(res)
 }
@@ -624,23 +638,20 @@ pub(crate) fn field_types_query(
 /// these are fine: `T: Foo<U::Item>, U: Foo<()>`.
 pub(crate) fn generic_predicates_for_param_query(
     db: &impl HirDatabase,
-    def: GenericDefId,
-    param_idx: u32,
+    param_id: TypeParamId,
 ) -> Arc<[GenericPredicate]> {
-    let resolver = def.resolver(db);
+    let resolver = param_id.parent.resolver(db);
     let ctx = TyLoweringContext::new(db, &resolver);
-    let generics = generics(db, def);
+    // let generics = generics(db, def);
     resolver
         .where_predicates_in_scope()
         // we have to filter out all other predicates *first*, before attempting to lower them
         .filter(|pred| match &pred.target {
             WherePredicateTarget::TypeRef(type_ref) => {
-                Ty::from_hir_only_param(&ctx, type_ref) == Some(param_idx)
+                Ty::from_hir_only_param(&ctx, type_ref) == Some(param_id)
             }
             WherePredicateTarget::TypeParam(local_id) => {
-                let param_id = hir_def::TypeParamId { parent: def, local_id: *local_id };
-                let idx = generics.param_idx(param_id);
-                idx == param_idx
+                *local_id == param_id.local_id
             }
         })
         .flat_map(|pred| GenericPredicate::from_where_predicate(&ctx, pred))
@@ -650,8 +661,7 @@ pub(crate) fn generic_predicates_for_param_query(
 pub(crate) fn generic_predicates_for_param_recover(
     _db: &impl HirDatabase,
     _cycle: &[String],
-    _def: &GenericDefId,
-    _param_idx: &u32,
+    _param_id: &TypeParamId,
 ) -> Arc<[GenericPredicate]> {
     Arc::new([])
 }
@@ -905,12 +915,12 @@ pub(crate) fn impl_self_ty_recover(
     Binders::new(generics.len(), Ty::Unknown)
 }
 
-pub(crate) fn impl_trait_query(db: &impl HirDatabase, impl_id: ImplId) -> Option<TraitRef> {
+pub(crate) fn impl_trait_query(db: &impl HirDatabase, impl_id: ImplId) -> Option<Binders<TraitRef>> {
     let impl_data = db.impl_data(impl_id);
     let resolver = impl_id.resolver(db);
-    let generics = generics(db, impl_id.into());
-    let ctx = TyLoweringContext::new(db, &resolver);
-    let self_ty = db.impl_self_ty(impl_id).subst(&Substs::identity(&generics));
+    let ctx = 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()?;
-    TraitRef::from_hir(&ctx, target_trait, Some(self_ty.clone()))
+    Some(Binders::new(self_ty.num_binders, TraitRef::from_hir(&ctx, target_trait, Some(self_ty.value.clone()))?))
 }
diff --git a/crates/ra_hir_ty/src/method_resolution.rs b/crates/ra_hir_ty/src/method_resolution.rs
index eab2149dc..5283bff28 100644
--- a/crates/ra_hir_ty/src/method_resolution.rs
+++ b/crates/ra_hir_ty/src/method_resolution.rs
@@ -61,7 +61,7 @@ impl CrateImplBlocks {
             for impl_id in module_data.scope.impls() {
                 match db.impl_trait(impl_id) {
                     Some(tr) => {
-                        res.impls_by_trait.entry(tr.trait_).or_default().push(impl_id);
+                        res.impls_by_trait.entry(tr.value.trait_).or_default().push(impl_id);
                     }
                     None => {
                         let self_ty = db.impl_self_ty(impl_id);
diff --git a/crates/ra_hir_ty/src/tests/method_resolution.rs b/crates/ra_hir_ty/src/tests/method_resolution.rs
index 446d12813..1722563aa 100644
--- a/crates/ra_hir_ty/src/tests/method_resolution.rs
+++ b/crates/ra_hir_ty/src/tests/method_resolution.rs
@@ -697,7 +697,7 @@ fn test<U, T: Trait<U>>(t: T) {
     [71; 72) 't': T
     [77; 96) '{     ...d(); }': ()
     [83; 84) 't': T
-    [83; 93) 't.method()': [missing name]
+    [83; 93) 't.method()': U
     "###
     );
 }
diff --git a/crates/ra_hir_ty/src/tests/traits.rs b/crates/ra_hir_ty/src/tests/traits.rs
index dc78e83cd..e6f697fa3 100644
--- a/crates/ra_hir_ty/src/tests/traits.rs
+++ b/crates/ra_hir_ty/src/tests/traits.rs
@@ -822,8 +822,7 @@ fn test<T: ApplyL>() {
 "#,
     );
     // inside the generic function, the associated type gets normalized to a placeholder `ApplL::Out<T>` [https://rust-lang.github.io/rustc-guide/traits/associated-types.html#placeholder-associated-types].
-    // FIXME: fix type parameter names going missing when going through Chalk
-    assert_eq!(t, "ApplyL::Out<[missing name]>");
+    assert_eq!(t, "ApplyL::Out<T>");
 }
 
 #[test]
diff --git a/crates/ra_hir_ty/src/traits/chalk.rs b/crates/ra_hir_ty/src/traits/chalk.rs
index fe9cb556c..6e97f7dd2 100644
--- a/crates/ra_hir_ty/src/traits/chalk.rs
+++ b/crates/ra_hir_ty/src/traits/chalk.rs
@@ -142,8 +142,9 @@ impl ToChalk for Ty {
                 let substitution = proj_ty.parameters.to_chalk(db);
                 chalk_ir::AliasTy { associated_ty_id, substitution }.cast().intern()
             }
-            Ty::Param { idx, .. } => {
-                PlaceholderIndex { ui: UniverseIndex::ROOT, idx: idx as usize }
+            Ty::Param(id) => {
+                let interned_id = db.intern_type_param_id(id);
+                PlaceholderIndex { ui: UniverseIndex::ROOT, idx: interned_id.as_intern_id().as_usize() }
                     .to_ty::<TypeFamily>()
             }
             Ty::Bound(idx) => chalk_ir::TyData::BoundVar(idx as usize).intern(),
@@ -177,7 +178,8 @@ impl ToChalk for Ty {
             },
             chalk_ir::TyData::Placeholder(idx) => {
                 assert_eq!(idx.ui, UniverseIndex::ROOT);
-                Ty::Param { idx: idx.idx as u32, name: crate::Name::missing() }
+                let interned_id = crate::db::GlobalTypeParamId::from_intern_id(crate::salsa::InternId::from(idx.idx));
+                Ty::Param(db.lookup_intern_type_param_id(interned_id))
             }
             chalk_ir::TyData::Alias(proj) => {
                 let associated_ty = from_chalk(db, proj.associated_ty_id);
@@ -524,7 +526,7 @@ fn convert_where_clauses(
             // skip errored predicates completely
             continue;
         }
-        result.push(pred.clone().subst(substs).to_chalk(db));
+        result.push(pred.clone().subst_type_params(db, def, substs).to_chalk(db));
     }
     result
 }
@@ -709,12 +711,12 @@ fn impl_block_datum(
     let trait_ref = db
         .impl_trait(impl_id)
         // ImplIds for impls where the trait ref can't be resolved should never reach Chalk
-        .expect("invalid impl passed to Chalk");
+        .expect("invalid impl passed to Chalk")
+        .value;
     let impl_data = db.impl_data(impl_id);
 
     let generic_params = generics(db, impl_id.into());
     let bound_vars = Substs::bound_vars(&generic_params);
-    let trait_ref = trait_ref.subst(&bound_vars);
     let trait_ = trait_ref.trait_;
     let impl_type = if impl_id.lookup(db).container.module(db).krate == krate {
         chalk_rust_ir::ImplType::Local
@@ -789,20 +791,18 @@ fn type_alias_associated_ty_value(
         _ => panic!("assoc ty value should be in impl"),
     };
 
-    let trait_ref = db.impl_trait(impl_id).expect("assoc ty value should not exist"); // we don't return any assoc ty values if the impl'd trait can't be resolved
+    let trait_ref = db.impl_trait(impl_id).expect("assoc ty value should not exist").value; // we don't return any assoc ty values if the impl'd trait can't be resolved
 
     let assoc_ty = db
         .trait_data(trait_ref.trait_)
         .associated_type_by_name(&type_alias_data.name)
         .expect("assoc ty value should not exist"); // validated when building the impl data as well
-    let generic_params = generics(db, impl_id.into());
-    let bound_vars = Substs::bound_vars(&generic_params);
-    let ty = db.ty(type_alias.into()).subst(&bound_vars);
-    let value_bound = chalk_rust_ir::AssociatedTyValueBound { ty: ty.to_chalk(db) };
+    let ty = db.ty(type_alias.into());
+    let value_bound = chalk_rust_ir::AssociatedTyValueBound { ty: ty.value.to_chalk(db) };
     let value = chalk_rust_ir::AssociatedTyValue {
         impl_id: Impl::ImplBlock(impl_id.into()).to_chalk(db),
         associated_ty_id: assoc_ty.to_chalk(db),
-        value: make_binders(value_bound, bound_vars.len()),
+        value: make_binders(value_bound, ty.num_binders),
     };
     Arc::new(value)
 }
diff --git a/crates/ra_hir_ty/src/utils.rs b/crates/ra_hir_ty/src/utils.rs
index 77b7de729..8fa1838bd 100644
--- a/crates/ra_hir_ty/src/utils.rs
+++ b/crates/ra_hir_ty/src/utils.rs
@@ -99,23 +99,19 @@ pub(crate) struct Generics {
 }
 
 impl Generics {
-    pub(crate) fn iter<'a>(&'a self) -> impl Iterator<Item = (u32, &'a TypeParamData)> + 'a {
+    pub(crate) fn iter<'a>(&'a self) -> impl Iterator<Item = (TypeParamId, &'a TypeParamData)> + 'a {
         self.parent_generics
             .as_ref()
             .into_iter()
-            .flat_map(|it| it.params.types.iter())
-            .chain(self.params.types.iter())
-            .enumerate()
-            .map(|(i, (_local_id, p))| (i as u32, p))
+            .flat_map(|it| it.params.types.iter().map(move |(local_id, p)| (TypeParamId { parent: it.def, local_id }, p)))
+            .chain(self.params.types.iter().map(move |(local_id, p)| (TypeParamId { parent: self.def, local_id }, p)))
     }
 
-    pub(crate) fn iter_parent<'a>(&'a self) -> impl Iterator<Item = (u32, &'a TypeParamData)> + 'a {
+    pub(crate) fn iter_parent<'a>(&'a self) -> impl Iterator<Item = (TypeParamId, &'a TypeParamData)> + 'a {
         self.parent_generics
             .as_ref()
             .into_iter()
-            .flat_map(|it| it.params.types.iter())
-            .enumerate()
-            .map(|(i, (_local_id, p))| (i as u32, p))
+            .flat_map(|it| it.params.types.iter().map(move |(local_id, p)| (TypeParamId { parent: it.def, local_id }, p)))
     }
 
     pub(crate) fn len(&self) -> usize {
@@ -137,16 +133,11 @@ impl Generics {
         (self_params, list_params, impl_trait_params)
     }
 
-    pub(crate) fn param_idx(&self, param: TypeParamId) -> u32 {
-        self.find_param(param).0
+    pub(crate) fn param_idx(&self, param: TypeParamId) -> Option<u32> {
+        Some(self.find_param(param)?.0)
     }
 
-    pub(crate) fn param_name(&self, param: TypeParamId) -> Name {
-        // FIXME make this return Option
-        self.find_param(param).1.name.clone().unwrap_or_else(Name::missing)
-    }
-
-    fn find_param(&self, param: TypeParamId) -> (u32, &TypeParamData) {
+    fn find_param(&self, param: TypeParamId) -> Option<(u32, &TypeParamData)> {
         if param.parent == self.def {
             let (idx, (_local_id, data)) = self
                 .params
@@ -156,9 +147,10 @@ impl Generics {
                 .find(|(_, (idx, _))| *idx == param.local_id)
                 .unwrap();
             let (_total, parent_len, _child) = self.len_split();
-            return ((parent_len + idx) as u32, data);
+            Some(((parent_len + idx) as u32, data))
+        } else {
+            self.parent_generics.as_ref().and_then(|g| g.find_param(param))
         }
-        self.parent_generics.as_ref().unwrap().find_param(param)
     }
 }