6 files changed, 30 insertions, 32 deletions

diff --git a/crates/ra_hir_ty/src/autoderef.rs b/crates/ra_hir_ty/src/autoderef.rs
index a6db7f623..d557962b4 100644
--- a/crates/ra_hir_ty/src/autoderef.rs
+++ b/crates/ra_hir_ty/src/autoderef.rs
@@ -55,7 +55,7 @@ fn deref_by_trait(
     let target = db.trait_data(deref_trait).associated_type_by_name(&name::TARGET_TYPE)?;
 
     let generic_params = generics(db, target.into());
-    if generic_params.count_params_including_parent() != 1 {
+    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 e52040eb5..2c296987c 100644
--- a/crates/ra_hir_ty/src/infer/expr.rs
+++ b/crates/ra_hir_ty/src/infer/expr.rs
@@ -660,10 +660,9 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
         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.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.as_ref().map(|p| p.iter_parent()) {
             for (_id, param) in parent_generics {
@@ -677,7 +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);
@@ -687,10 +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())
     }
 
@@ -709,9 +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(
-                                generics(self.db, 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 99fd7158e..036d3a589 100644
--- a/crates/ra_hir_ty/src/lib.rs
+++ b/crates/ra_hir_ty/src/lib.rs
@@ -167,15 +167,15 @@ impl TypeCtor {
             => 1,
             TypeCtor::Adt(adt) => {
                 let generic_params = generics(db, AdtId::from(adt).into());
-                generic_params.count_params_including_parent()
+                generic_params.len()
             }
             TypeCtor::FnDef(callable) => {
                 let generic_params = generics(db, callable.into());
-                generic_params.count_params_including_parent()
+                generic_params.len()
             }
             TypeCtor::AssociatedType(type_alias) => {
                 let generic_params = generics(db, type_alias.into());
-                generic_params.count_params_including_parent()
+                generic_params.len()
             }
             TypeCtor::FnPtr { num_args } => num_args as usize + 1,
             TypeCtor::Tuple { cardinality } => cardinality as usize,
@@ -378,12 +378,12 @@ impl Substs {
     pub fn build_for_def(db: &impl HirDatabase, def: impl Into<GenericDefId>) -> SubstsBuilder {
         let def = def.into();
         let params = generics(db, def);
-        let param_count = params.count_params_including_parent();
+        let param_count = params.len();
         Substs::builder(param_count)
     }
 
     pub(crate) fn build_for_generics(generic_params: &Generics) -> SubstsBuilder {
-        Substs::builder(generic_params.count_params_including_parent())
+        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 d31f6a2d2..eab91229e 100644
--- a/crates/ra_hir_ty/src/lower.rs
+++ b/crates/ra_hir_ty/src/lower.rs
@@ -321,9 +321,8 @@ pub(super) fn substs_from_path_segment(
     let mut substs = Vec::new();
     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.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
@@ -334,8 +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);
@@ -346,10 +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 {
diff --git a/crates/ra_hir_ty/src/traits/chalk.rs b/crates/ra_hir_ty/src/traits/chalk.rs
index 1d44320b9..1e7ff93d5 100644
--- a/crates/ra_hir_ty/src/traits/chalk.rs
+++ b/crates/ra_hir_ty/src/traits/chalk.rs
@@ -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)
 }
diff --git a/crates/ra_hir_ty/src/utils.rs b/crates/ra_hir_ty/src/utils.rs
index 2c458867f..936cfe25e 100644
--- a/crates/ra_hir_ty/src/utils.rs
+++ b/crates/ra_hir_ty/src/utils.rs
@@ -117,13 +117,14 @@ impl Generics {
             .map(|(i, (_local_id, p))| (i as u32, p))
     }
 
-    pub(crate) fn count_parent_params(&self) -> usize {
-        self.parent_generics.as_ref().map_or(0, |p| p.count_params_including_parent())
+    pub(crate) fn len(&self) -> usize {
+        self.len_split().0
     }
-
-    pub(crate) fn count_params_including_parent(&self) -> usize {
-        let parent_count = self.count_parent_params();
-        parent_count + self.params.params.len()
+    /// (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.params.len();
+        (parent + child, parent, child)
     }
     pub(crate) fn param_idx(&self, param: GenericParamId) -> u32 {
         self.find_param(param).0
@@ -140,8 +141,8 @@ impl Generics {
                 .enumerate()
                 .find(|(_, (idx, _))| *idx == param.local_id)
                 .unwrap();
-
-            return ((self.count_parent_params() + idx) as u32, data);
+            let (_total, parent_len, _child) = self.len_split();
+            return ((parent_len + idx) as u32, data);
         }
         self.parent_generics.as_ref().unwrap().find_param(param)
     }