7 files changed, 156 insertions, 83 deletions

diff --git a/crates/ra_hir_ty/src/autoderef.rs b/crates/ra_hir_ty/src/autoderef.rs
index 9d1d4e48c..d557962b4 100644
--- a/crates/ra_hir_ty/src/autoderef.rs
+++ b/crates/ra_hir_ty/src/autoderef.rs
@@ -10,10 +10,10 @@ use hir_expand::name;
 use log::{info, warn};
 use ra_db::CrateId;
 
-use crate::db::HirDatabase;
-
-use super::{
+use crate::{
+    db::HirDatabase,
     traits::{InEnvironment, Solution},
+    utils::generics,
     Canonical, Substs, Ty, TypeWalk,
 };
 
@@ -54,8 +54,8 @@ fn deref_by_trait(
     };
     let target = db.trait_data(deref_trait).associated_type_by_name(&name::TARGET_TYPE)?;
 
-    let generic_params = db.generic_params(target.into());
-    if generic_params.count_params_including_parent() != 1 {
+    let generic_params = generics(db, target.into());
+    if generic_params.len() != 1 {
         // the Target type + Deref trait should only have one generic parameter,
         // namely Deref's Self type
         return None;
diff --git a/crates/ra_hir_ty/src/infer/expr.rs b/crates/ra_hir_ty/src/infer/expr.rs
index b8df27706..2c296987c 100644
--- a/crates/ra_hir_ty/src/infer/expr.rs
+++ b/crates/ra_hir_ty/src/infer/expr.rs
@@ -6,7 +6,6 @@ use std::sync::Arc;
 use hir_def::{
     builtin_type::Signedness,
     expr::{Array, BinaryOp, Expr, ExprId, Literal, Statement, UnaryOp},
-    generics::GenericParams,
     path::{GenericArg, GenericArgs},
     resolver::resolver_for_expr,
     AdtId, ContainerId, Lookup, StructFieldId,
@@ -15,7 +14,11 @@ use hir_expand::name::{self, Name};
 use ra_syntax::ast::RangeOp;
 
 use crate::{
-    autoderef, db::HirDatabase, method_resolution, op, traits::InEnvironment, utils::variant_data,
+    autoderef,
+    db::HirDatabase,
+    method_resolution, op,
+    traits::InEnvironment,
+    utils::{generics, variant_data, Generics},
     CallableDef, InferTy, IntTy, Mutability, Obligation, ProjectionPredicate, ProjectionTy, Substs,
     TraitRef, Ty, TypeCtor, TypeWalk, Uncertain,
 };
@@ -596,7 +599,7 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
             Some((ty, func)) => {
                 let ty = canonicalized_receiver.decanonicalize_ty(ty);
                 self.write_method_resolution(tgt_expr, func);
-                (ty, self.db.value_ty(func.into()), Some(self.db.generic_params(func.into())))
+                (ty, self.db.value_ty(func.into()), Some(generics(self.db, func.into())))
             }
             None => (receiver_ty, Ty::Unknown, None),
         };
@@ -653,16 +656,16 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
 
     fn substs_for_method_call(
         &mut self,
-        def_generics: Option<Arc<GenericParams>>,
+        def_generics: Option<Generics>,
         generic_args: Option<&GenericArgs>,
         receiver_ty: &Ty,
     ) -> Substs {
-        let (parent_param_count, param_count) =
-            def_generics.as_ref().map_or((0, 0), |g| (g.count_parent_params(), g.params.len()));
-        let mut substs = Vec::with_capacity(parent_param_count + param_count);
+        let (total_len, _parent_len, child_len) =
+            def_generics.as_ref().map_or((0, 0, 0), |g| g.len_split());
+        let mut substs = Vec::with_capacity(total_len);
         // Parent arguments are unknown, except for the receiver type
-        if let Some(parent_generics) = def_generics.and_then(|p| p.parent_params.clone()) {
-            for param in &parent_generics.params {
+        if let Some(parent_generics) = def_generics.as_ref().map(|p| p.iter_parent()) {
+            for (_id, param) in parent_generics {
                 if param.name == name::SELF_TYPE {
                     substs.push(receiver_ty.clone());
                 } else {
@@ -673,7 +676,7 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
         // handle provided type arguments
         if let Some(generic_args) = generic_args {
             // if args are provided, it should be all of them, but we can't rely on that
-            for arg in generic_args.args.iter().take(param_count) {
+            for arg in generic_args.args.iter().take(child_len) {
                 match arg {
                     GenericArg::Type(type_ref) => {
                         let ty = self.make_ty(type_ref);
@@ -683,10 +686,10 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
             }
         };
         let supplied_params = substs.len();
-        for _ in supplied_params..parent_param_count + param_count {
+        for _ in supplied_params..total_len {
             substs.push(Ty::Unknown);
         }
-        assert_eq!(substs.len(), parent_param_count + param_count);
+        assert_eq!(substs.len(), total_len);
         Substs(substs.into())
     }
 
@@ -705,11 +708,8 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
                     CallableDef::FunctionId(f) => {
                         if let ContainerId::TraitId(trait_) = f.lookup(self.db).container {
                             // construct a TraitDef
-                            let substs = a_ty.parameters.prefix(
-                                self.db
-                                    .generic_params(trait_.into())
-                                    .count_params_including_parent(),
-                            );
+                            let substs =
+                                a_ty.parameters.prefix(generics(self.db, trait_.into()).len());
                             self.obligations.push(Obligation::Trait(TraitRef {
                                 trait_: trait_.into(),
                                 substs,
diff --git a/crates/ra_hir_ty/src/lib.rs b/crates/ra_hir_ty/src/lib.rs
index 3c1f738df..3ad913e55 100644
--- a/crates/ra_hir_ty/src/lib.rs
+++ b/crates/ra_hir_ty/src/lib.rs
@@ -44,8 +44,8 @@ use std::sync::Arc;
 use std::{fmt, iter, mem};
 
 use hir_def::{
-    expr::ExprId, generics::GenericParams, type_ref::Mutability, AdtId, ContainerId, DefWithBodyId,
-    GenericDefId, HasModule, Lookup, TraitId, TypeAliasId,
+    expr::ExprId, type_ref::Mutability, AdtId, ContainerId, DefWithBodyId, GenericDefId, HasModule,
+    Lookup, TraitId, TypeAliasId,
 };
 use hir_expand::name::Name;
 use ra_db::{impl_intern_key, salsa, CrateId};
@@ -53,7 +53,7 @@ use ra_db::{impl_intern_key, salsa, CrateId};
 use crate::{
     db::HirDatabase,
     primitive::{FloatTy, IntTy, Uncertain},
-    utils::make_mut_slice,
+    utils::{generics, make_mut_slice, Generics},
 };
 use display::{HirDisplay, HirFormatter};
 
@@ -166,16 +166,16 @@ impl TypeCtor {
             | TypeCtor::Closure { .. } // 1 param representing the signature of the closure
             => 1,
             TypeCtor::Adt(adt) => {
-                let generic_params = db.generic_params(AdtId::from(adt).into());
-                generic_params.count_params_including_parent()
+                let generic_params = generics(db, AdtId::from(adt).into());
+                generic_params.len()
             }
             TypeCtor::FnDef(callable) => {
-                let generic_params = db.generic_params(callable.into());
-                generic_params.count_params_including_parent()
+                let generic_params = generics(db, callable.into());
+                generic_params.len()
             }
             TypeCtor::AssociatedType(type_alias) => {
-                let generic_params = db.generic_params(type_alias.into());
-                generic_params.count_params_including_parent()
+                let generic_params = generics(db, type_alias.into());
+                generic_params.len()
             }
             TypeCtor::FnPtr { num_args } => num_args as usize + 1,
             TypeCtor::Tuple { cardinality } => cardinality as usize,
@@ -364,36 +364,26 @@ impl Substs {
     }
 
     /// Return Substs that replace each parameter by itself (i.e. `Ty::Param`).
-    pub fn identity(generic_params: &GenericParams) -> Substs {
+    pub(crate) fn identity(generic_params: &Generics) -> Substs {
         Substs(
-            generic_params
-                .params_including_parent()
-                .into_iter()
-                .map(|p| Ty::Param { idx: p.idx, name: p.name.clone() })
-                .collect(),
+            generic_params.iter().map(|(idx, p)| Ty::Param { idx, name: p.name.clone() }).collect(),
         )
     }
 
     /// Return Substs that replace each parameter by a bound variable.
-    pub fn bound_vars(generic_params: &GenericParams) -> Substs {
-        Substs(
-            generic_params
-                .params_including_parent()
-                .into_iter()
-                .map(|p| Ty::Bound(p.idx))
-                .collect(),
-        )
+    pub(crate) fn bound_vars(generic_params: &Generics) -> Substs {
+        Substs(generic_params.iter().map(|(idx, _p)| Ty::Bound(idx)).collect())
     }
 
     pub fn build_for_def(db: &impl HirDatabase, def: impl Into<GenericDefId>) -> SubstsBuilder {
         let def = def.into();
-        let params = db.generic_params(def);
-        let param_count = params.count_params_including_parent();
+        let params = generics(db, def);
+        let param_count = params.len();
         Substs::builder(param_count)
     }
 
-    pub fn build_for_generics(generic_params: &GenericParams) -> SubstsBuilder {
-        Substs::builder(generic_params.count_params_including_parent())
+    pub(crate) fn build_for_generics(generic_params: &Generics) -> SubstsBuilder {
+        Substs::builder(generic_params.len())
     }
 
     pub fn build_for_type_ctor(db: &impl HirDatabase, type_ctor: TypeCtor) -> SubstsBuilder {
diff --git a/crates/ra_hir_ty/src/lower.rs b/crates/ra_hir_ty/src/lower.rs
index 32569ac66..eab91229e 100644
--- a/crates/ra_hir_ty/src/lower.rs
+++ b/crates/ra_hir_ty/src/lower.rs
@@ -24,7 +24,7 @@ use crate::{
     db::HirDatabase,
     primitive::{FloatTy, IntTy},
     utils::{
-        all_super_traits, associated_type_by_name_including_super_traits, make_mut_slice,
+        all_super_traits, associated_type_by_name_including_super_traits, generics, make_mut_slice,
         variant_data,
     },
     FnSig, GenericPredicate, ProjectionPredicate, ProjectionTy, Substs, TraitEnvironment, TraitRef,
@@ -111,7 +111,9 @@ impl Ty {
             Some((it, None)) => it,
             _ => return None,
         };
-        if let TypeNs::GenericParam(idx) = resolution {
+        if let TypeNs::GenericParam(param_id) = resolution {
+            let generics = generics(db, resolver.generic_def().expect("generics in scope"));
+            let idx = generics.param_idx(param_id);
             Some(idx)
         } else {
             None
@@ -174,9 +176,11 @@ impl Ty {
                     Ty::Dyn(Arc::new([GenericPredicate::Implemented(trait_ref)]))
                 };
             }
-            TypeNs::GenericParam(idx) => {
+            TypeNs::GenericParam(param_id) => {
+                let generics = generics(db, resolver.generic_def().expect("generics in scope"));
+                let idx = generics.param_idx(param_id);
                 // FIXME: maybe return name in resolution?
-                let name = resolved_segment.name.clone();
+                let name = generics.param_name(param_id);
                 Ty::Param { idx, name }
             }
             TypeNs::SelfType(impl_id) => db.impl_self_ty(impl_id).clone(),
@@ -315,11 +319,10 @@ pub(super) fn substs_from_path_segment(
     add_self_param: bool,
 ) -> Substs {
     let mut substs = Vec::new();
-    let def_generics = def_generic.map(|def| db.generic_params(def.into()));
+    let def_generics = def_generic.map(|def| generics(db, def.into()));
 
-    let (parent_param_count, param_count) =
-        def_generics.map_or((0, 0), |g| (g.count_parent_params(), g.params.len()));
-    substs.extend(iter::repeat(Ty::Unknown).take(parent_param_count));
+    let (total_len, parent_len, child_len) = def_generics.map_or((0, 0, 0), |g| g.len_split());
+    substs.extend(iter::repeat(Ty::Unknown).take(parent_len));
     if add_self_param {
         // FIXME this add_self_param argument is kind of a hack: Traits have the
         // Self type as an implicit first type parameter, but it can't be
@@ -330,8 +333,8 @@ pub(super) fn substs_from_path_segment(
     if let Some(generic_args) = &segment.args_and_bindings {
         // if args are provided, it should be all of them, but we can't rely on that
         let self_param_correction = if add_self_param { 1 } else { 0 };
-        let param_count = param_count - self_param_correction;
-        for arg in generic_args.args.iter().take(param_count) {
+        let child_len = child_len + self_param_correction;
+        for arg in generic_args.args.iter().take(child_len) {
             match arg {
                 GenericArg::Type(type_ref) => {
                     let ty = Ty::from_hir(db, resolver, type_ref);
@@ -342,10 +345,10 @@ pub(super) fn substs_from_path_segment(
     }
     // add placeholders for args that were not provided
     let supplied_params = substs.len();
-    for _ in supplied_params..parent_param_count + param_count {
+    for _ in supplied_params..total_len {
         substs.push(Ty::Unknown);
     }
-    assert_eq!(substs.len(), parent_param_count + param_count);
+    assert_eq!(substs.len(), total_len);
 
     // handle defaults
     if let Some(def_generic) = def_generic {
@@ -567,12 +570,11 @@ pub(crate) fn generic_predicates_query(
 /// Resolve the default type params from generics
 pub(crate) fn generic_defaults_query(db: &impl HirDatabase, def: GenericDefId) -> Substs {
     let resolver = def.resolver(db);
-    let generic_params = db.generic_params(def.into());
+    let generic_params = generics(db, def.into());
 
     let defaults = generic_params
-        .params_including_parent()
-        .into_iter()
-        .map(|p| p.default.as_ref().map_or(Ty::Unknown, |t| Ty::from_hir(db, &resolver, t)))
+        .iter()
+        .map(|(_idx, p)| p.default.as_ref().map_or(Ty::Unknown, |t| Ty::from_hir(db, &resolver, t)))
         .collect();
 
     Substs(defaults)
@@ -589,7 +591,7 @@ fn fn_sig_for_fn(db: &impl HirDatabase, def: FunctionId) -> FnSig {
 /// Build the declared type of a function. This should not need to look at the
 /// function body.
 fn type_for_fn(db: &impl HirDatabase, def: FunctionId) -> Ty {
-    let generics = db.generic_params(def.into());
+    let generics = generics(db, def.into());
     let substs = Substs::identity(&generics);
     Ty::apply(TypeCtor::FnDef(def.into()), substs)
 }
@@ -639,7 +641,7 @@ fn type_for_struct_constructor(db: &impl HirDatabase, def: StructId) -> Ty {
     if struct_data.variant_data.is_unit() {
         return type_for_adt(db, def.into()); // Unit struct
     }
-    let generics = db.generic_params(def.into());
+    let generics = generics(db, def.into());
     let substs = Substs::identity(&generics);
     Ty::apply(TypeCtor::FnDef(def.into()), substs)
 }
@@ -653,7 +655,7 @@ fn fn_sig_for_enum_variant_constructor(db: &impl HirDatabase, def: EnumVariantId
         .iter()
         .map(|(_, field)| Ty::from_hir(db, &resolver, &field.type_ref))
         .collect::<Vec<_>>();
-    let generics = db.generic_params(def.parent.into());
+    let generics = generics(db, def.parent.into());
     let substs = Substs::identity(&generics);
     let ret = type_for_adt(db, def.parent.into()).subst(&substs);
     FnSig::from_params_and_return(params, ret)
@@ -666,18 +668,18 @@ fn type_for_enum_variant_constructor(db: &impl HirDatabase, def: EnumVariantId)
     if var_data.is_unit() {
         return type_for_adt(db, def.parent.into()); // Unit variant
     }
-    let generics = db.generic_params(def.parent.into());
+    let generics = generics(db, def.parent.into());
     let substs = Substs::identity(&generics);
     Ty::apply(TypeCtor::FnDef(EnumVariantId::from(def).into()), substs)
 }
 
 fn type_for_adt(db: &impl HirDatabase, adt: AdtId) -> Ty {
-    let generics = db.generic_params(adt.into());
+    let generics = generics(db, adt.into());
     Ty::apply(TypeCtor::Adt(adt), Substs::identity(&generics))
 }
 
 fn type_for_type_alias(db: &impl HirDatabase, t: TypeAliasId) -> Ty {
-    let generics = db.generic_params(t.into());
+    let generics = generics(db, t.into());
     let resolver = t.resolver(db);
     let type_ref = &db.type_alias_data(t).type_ref;
     let substs = Substs::identity(&generics);
diff --git a/crates/ra_hir_ty/src/tests.rs b/crates/ra_hir_ty/src/tests.rs
index f1b67555f..d724ee122 100644
--- a/crates/ra_hir_ty/src/tests.rs
+++ b/crates/ra_hir_ty/src/tests.rs
@@ -11,8 +11,8 @@ use std::fmt::Write;
 use std::sync::Arc;
 
 use hir_def::{
-    body::BodySourceMap, child_from_source::ChildFromSource, db::DefDatabase, nameres::CrateDefMap,
-    AssocItemId, DefWithBodyId, LocalModuleId, Lookup, ModuleDefId,
+    body::BodySourceMap, child_by_source::ChildBySource, db::DefDatabase, keys,
+    nameres::CrateDefMap, AssocItemId, DefWithBodyId, LocalModuleId, Lookup, ModuleDefId,
 };
 use hir_expand::InFile;
 use insta::assert_snapshot;
@@ -33,7 +33,9 @@ fn type_at_pos(db: &TestDB, pos: FilePosition) -> String {
     let expr = algo::find_node_at_offset::<ast::Expr>(file.syntax(), pos.offset).unwrap();
     let fn_def = expr.syntax().ancestors().find_map(ast::FnDef::cast).unwrap();
     let module = db.module_for_file(pos.file_id);
-    let func = module.child_from_source(db, InFile::new(pos.file_id.into(), fn_def)).unwrap();
+    let func = *module.child_by_source(db)[keys::FUNCTION]
+        .get(&InFile::new(pos.file_id.into(), fn_def))
+        .unwrap();
 
     let (_body, source_map) = db.body_with_source_map(func.into());
     if let Some(expr_id) = source_map.node_expr(InFile::new(pos.file_id.into(), &expr)) {
diff --git a/crates/ra_hir_ty/src/traits/chalk.rs b/crates/ra_hir_ty/src/traits/chalk.rs
index e3f02fa15..1e7ff93d5 100644
--- a/crates/ra_hir_ty/src/traits/chalk.rs
+++ b/crates/ra_hir_ty/src/traits/chalk.rs
@@ -19,8 +19,8 @@ use ra_db::{
 
 use super::{builtin, AssocTyValue, Canonical, ChalkContext, Impl, Obligation};
 use crate::{
-    db::HirDatabase, display::HirDisplay, ApplicationTy, GenericPredicate, ProjectionTy, Substs,
-    TraitRef, Ty, TypeCtor, TypeWalk,
+    db::HirDatabase, display::HirDisplay, utils::generics, ApplicationTy, GenericPredicate,
+    ProjectionTy, Substs, TraitRef, Ty, TypeCtor, TypeWalk,
 };
 
 /// This represents a trait whose name we could not resolve.
@@ -547,7 +547,7 @@ pub(crate) fn associated_ty_data_query(
         ContainerId::TraitId(t) => t,
         _ => panic!("associated type not in trait"),
     };
-    let generic_params = db.generic_params(type_alias.into());
+    let generic_params = generics(db, type_alias.into());
     let bound_data = chalk_rust_ir::AssociatedTyDatumBound {
         // FIXME add bounds and where clauses
         bounds: vec![],
@@ -557,7 +557,7 @@ pub(crate) fn associated_ty_data_query(
         trait_id: trait_.to_chalk(db),
         id,
         name: lalrpop_intern::intern(&db.type_alias_data(type_alias).name.to_string()),
-        binders: make_binders(bound_data, generic_params.count_params_including_parent()),
+        binders: make_binders(bound_data, generic_params.len()),
     };
     Arc::new(datum)
 }
@@ -589,7 +589,7 @@ pub(crate) fn trait_datum_query(
     let trait_: TraitId = from_chalk(db, trait_id);
     let trait_data = db.trait_data(trait_);
     debug!("trait {:?} = {:?}", trait_id, trait_data.name);
-    let generic_params = db.generic_params(trait_.into());
+    let generic_params = generics(db, trait_.into());
     let bound_vars = Substs::bound_vars(&generic_params);
     let flags = chalk_rust_ir::TraitFlags {
         auto: trait_data.auto,
@@ -626,7 +626,7 @@ pub(crate) fn struct_datum_query(
     let where_clauses = type_ctor
         .as_generic_def()
         .map(|generic_def| {
-            let generic_params = db.generic_params(generic_def.into());
+            let generic_params = generics(db, generic_def.into());
             let bound_vars = Substs::bound_vars(&generic_params);
             convert_where_clauses(db, generic_def, &bound_vars)
         })
@@ -669,7 +669,7 @@ fn impl_block_datum(
     let trait_ref = db.impl_trait(impl_id)?;
     let impl_data = db.impl_data(impl_id);
 
-    let generic_params = db.generic_params(impl_id.into());
+    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_;
@@ -767,7 +767,7 @@ fn type_alias_associated_ty_value(
         .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 = db.generic_params(impl_id.into());
+    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) };
diff --git a/crates/ra_hir_ty/src/utils.rs b/crates/ra_hir_ty/src/utils.rs
index e4ba890ef..aeb211a91 100644
--- a/crates/ra_hir_ty/src/utils.rs
+++ b/crates/ra_hir_ty/src/utils.rs
@@ -5,9 +5,10 @@ use std::sync::Arc;
 use hir_def::{
     adt::VariantData,
     db::DefDatabase,
+    generics::{GenericParams, TypeParamData},
     resolver::{HasResolver, TypeNs},
     type_ref::TypeRef,
-    TraitId, TypeAliasId, VariantId,
+    ContainerId, GenericDefId, Lookup, TraitId, TypeAliasId, TypeParamId, VariantId,
 };
 use hir_expand::name::{self, Name};
 
@@ -82,3 +83,81 @@ pub(crate) fn make_mut_slice<T: Clone>(a: &mut Arc<[T]>) -> &mut [T] {
     }
     Arc::get_mut(a).unwrap()
 }
+
+pub(crate) fn generics(db: &impl DefDatabase, def: GenericDefId) -> Generics {
+    let parent_generics = parent_generic_def(db, def).map(|def| Box::new(generics(db, def)));
+    Generics { def, params: db.generic_params(def), parent_generics }
+}
+
+pub(crate) struct Generics {
+    def: GenericDefId,
+    pub(crate) params: Arc<GenericParams>,
+    parent_generics: Option<Box<Generics>>,
+}
+
+impl Generics {
+    pub(crate) fn iter<'a>(&'a self) -> impl Iterator<Item = (u32, &'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))
+    }
+
+    pub(crate) fn iter_parent<'a>(&'a self) -> impl Iterator<Item = (u32, &'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))
+    }
+
+    pub(crate) fn len(&self) -> usize {
+        self.len_split().0
+    }
+    /// (total, parents, child)
+    pub(crate) fn len_split(&self) -> (usize, usize, usize) {
+        let parent = self.parent_generics.as_ref().map_or(0, |p| p.len());
+        let child = self.params.types.len();
+        (parent + child, parent, child)
+    }
+    pub(crate) fn param_idx(&self, param: TypeParamId) -> u32 {
+        self.find_param(param).0
+    }
+    pub(crate) fn param_name(&self, param: TypeParamId) -> Name {
+        self.find_param(param).1.name.clone()
+    }
+    fn find_param(&self, param: TypeParamId) -> (u32, &TypeParamData) {
+        if param.parent == self.def {
+            let (idx, (_local_id, data)) = self
+                .params
+                .types
+                .iter()
+                .enumerate()
+                .find(|(_, (idx, _))| *idx == param.local_id)
+                .unwrap();
+            let (_total, parent_len, _child) = self.len_split();
+            return ((parent_len + idx) as u32, data);
+        }
+        self.parent_generics.as_ref().unwrap().find_param(param)
+    }
+}
+
+fn parent_generic_def(db: &impl DefDatabase, def: GenericDefId) -> Option<GenericDefId> {
+    let container = match def {
+        GenericDefId::FunctionId(it) => it.lookup(db).container,
+        GenericDefId::TypeAliasId(it) => it.lookup(db).container,
+        GenericDefId::ConstId(it) => it.lookup(db).container,
+        GenericDefId::EnumVariantId(it) => return Some(it.parent.into()),
+        GenericDefId::AdtId(_) | GenericDefId::TraitId(_) | GenericDefId::ImplId(_) => return None,
+    };
+
+    match container {
+        ContainerId::ImplId(it) => Some(it.into()),
+        ContainerId::TraitId(it) => Some(it.into()),
+        ContainerId::ModuleId(_) => None,
+    }
+}