Lower impl trait to variables, move away from using placeholders where they don't belong

1 files changed, 17 insertions, 38 deletions

diff --git a/crates/ra_hir_ty/src/infer/path.rs b/crates/ra_hir_ty/src/infer/path.rs
index 02fc99288..39aa346eb 100644
--- a/crates/ra_hir_ty/src/infer/path.rs
+++ b/crates/ra_hir_ty/src/infer/path.rs
@@ -10,8 +10,8 @@ use hir_def::{
 use hir_expand::name::Name;
 
 use crate::{
-    db::HirDatabase, lower::ImplTraitLoweringMode, method_resolution, Substs, Ty, TypeWalk,
-    ValueTyDefId,
+    db::HirDatabase, method_resolution, Substs, Ty,
+    ValueTyDefId
 };
 
 use super::{ExprOrPatId, InferenceContext, TraitRef};
@@ -42,11 +42,7 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
             }
             let ty = self.make_ty(type_ref);
             let remaining_segments_for_ty = path.segments().take(path.segments().len() - 1);
-            let ctx = crate::lower::TyLoweringContext {
-                db: self.db,
-                resolver: &resolver,
-                impl_trait_mode: ImplTraitLoweringMode::Disallowed,
-            };
+            let ctx = crate::lower::TyLoweringContext::new(self.db, &resolver);
             let ty = Ty::from_type_relative_path(&ctx, ty, remaining_segments_for_ty);
             self.resolve_ty_assoc_item(
                 ty,
@@ -77,17 +73,16 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
             ValueNs::EnumVariantId(it) => it.into(),
         };
 
-        let mut ty = self.db.value_ty(typable);
-        if let Some(self_subst) = self_subst {
-            ty = ty.subst(&self_subst);
-        }
-        let ctx = crate::lower::TyLoweringContext {
-            db: self.db,
-            resolver: &self.resolver,
-            impl_trait_mode: ImplTraitLoweringMode::Disallowed,
-        };
+        let ty = self.db.value_ty(typable);
+        // self_subst is just for the parent
+        let parent_substs = self_subst.unwrap_or_else(Substs::empty);
+        let ctx = crate::lower::TyLoweringContext::new(self.db, &self.resolver);
         let substs = Ty::substs_from_path(&ctx, path, typable);
-        let ty = ty.subst(&substs);
+        let full_substs = Substs::builder(substs.len())
+            .use_parent_substs(&parent_substs)
+            .fill(substs.0[parent_substs.len()..].iter().cloned())
+            .build();
+        let ty = ty.subst(&full_substs);
         Some(ty)
     }
 
@@ -111,11 +106,7 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
             (TypeNs::TraitId(trait_), true) => {
                 let segment =
                     remaining_segments.last().expect("there should be at least one segment here");
-                let ctx = crate::lower::TyLoweringContext {
-                    db: self.db,
-                    resolver: &self.resolver,
-                    impl_trait_mode: ImplTraitLoweringMode::Disallowed,
-                };
+                let ctx = crate::lower::TyLoweringContext::new(self.db, &self.resolver);
                 let trait_ref =
                     TraitRef::from_resolved_path(&ctx, trait_.into(), resolved_segment, None);
                 self.resolve_trait_assoc_item(trait_ref, segment, id)
@@ -127,11 +118,7 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
                 // as Iterator>::Item::default`)
                 let remaining_segments_for_ty =
                     remaining_segments.take(remaining_segments.len() - 1);
-                let ctx = crate::lower::TyLoweringContext {
-                    db: self.db,
-                    resolver: &self.resolver,
-                    impl_trait_mode: ImplTraitLoweringMode::Disallowed,
-                };
+                let ctx = crate::lower::TyLoweringContext::new(self.db, &self.resolver);
                 let ty = Ty::from_partly_resolved_hir_path(
                     &ctx,
                     def,
@@ -235,12 +222,8 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
                             .fill(iter::repeat_with(|| self.table.new_type_var()))
                             .build();
                         let impl_self_ty = self.db.impl_self_ty(impl_id).subst(&impl_substs);
-                        let substs = Substs::build_for_def(self.db, item)
-                            .use_parent_substs(&impl_substs)
-                            .fill_with_params()
-                            .build();
                         self.unify(&impl_self_ty, &ty);
-                        Some(substs)
+                        Some(impl_substs)
                     }
                     AssocContainerId::TraitId(trait_) => {
                         // we're picking this method
@@ -248,15 +231,11 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
                             .push(ty.clone())
                             .fill(std::iter::repeat_with(|| self.table.new_type_var()))
                             .build();
-                        let substs = Substs::build_for_def(self.db, item)
-                            .use_parent_substs(&trait_substs)
-                            .fill_with_params()
-                            .build();
                         self.obligations.push(super::Obligation::Trait(TraitRef {
                             trait_,
-                            substs: trait_substs,
+                            substs: trait_substs.clone(),
                         }));
-                        Some(substs)
+                        Some(trait_substs)
                     }
                     AssocContainerId::ContainerId(_) => None,
                 };