4 files changed, 115 insertions, 101 deletions

diff --git a/crates/ra_hir_ty/src/infer.rs b/crates/ra_hir_ty/src/infer.rs
index 0d65984ee..8d5b7c943 100644
--- a/crates/ra_hir_ty/src/infer.rs
+++ b/crates/ra_hir_ty/src/infer.rs
@@ -479,8 +479,11 @@ impl<'a, D: HirDatabase> InferenceContext<'a, D> {
 
     fn collect_fn(&mut self, data: &FunctionData) {
         let body = Arc::clone(&self.body); // avoid borrow checker problem
-        for (type_ref, pat) in data.params.iter().zip(body.params.iter()) {
-            let ty = self.make_ty_with_mode(type_ref, ImplTraitLoweringMode::Param);
+        let ctx = crate::lower::TyLoweringContext::new(self.db, &self.resolver).with_impl_trait_mode(ImplTraitLoweringMode::Param);
+        let param_tys = data.params.iter().map(|type_ref| Ty::from_hir(&ctx, type_ref)).collect::<Vec<_>>();
+        for (ty, pat) in param_tys.into_iter().zip(body.params.iter()) {
+            let ty = self.insert_type_vars(ty);
+            let ty = self.normalize_associated_types_in(ty);
 
             self.infer_pat(*pat, &ty, BindingMode::default());
         }
diff --git a/crates/ra_hir_ty/src/lib.rs b/crates/ra_hir_ty/src/lib.rs
index 1e162943c..6eccd7fa8 100644
--- a/crates/ra_hir_ty/src/lib.rs
+++ b/crates/ra_hir_ty/src/lib.rs
@@ -44,11 +44,11 @@ use std::sync::Arc;
 use std::{fmt, iter, mem};
 
 use hir_def::{
-    expr::ExprId, type_ref::Mutability, AdtId, AssocContainerId, DefWithBodyId, GenericDefId,
-    HasModule, Lookup, TraitId, TypeAliasId, TypeParamId, generics::TypeParamProvenance,
+    expr::ExprId, generics::TypeParamProvenance, type_ref::Mutability, AdtId, AssocContainerId,
+    DefWithBodyId, GenericDefId, HasModule, Lookup, TraitId, TypeAliasId, TypeParamId,
 };
-use ra_db::{impl_intern_key, salsa, CrateId};
 use hir_expand::name::Name;
+use ra_db::{impl_intern_key, salsa, CrateId};
 
 use crate::{
     db::HirDatabase,
@@ -360,9 +360,7 @@ impl Substs {
 
     /// Return Substs that replace each parameter by itself (i.e. `Ty::Param`).
     pub(crate) fn type_params(generic_params: &Generics) -> Substs {
-        Substs(
-            generic_params.iter().map(|(id, _)| Ty::Param(id)).collect(),
-        )
+        Substs(generic_params.iter().map(|(id, _)| Ty::Param(id)).collect())
     }
 
     /// Return Substs that replace each parameter by a bound variable.
@@ -448,7 +446,9 @@ pub struct Binders<T> {
 }
 
 impl<T> Binders<T> {
-    pub fn new(num_binders: usize, value: T) -> Self { Self { num_binders, value } }
+    pub fn new(num_binders: usize, value: T) -> Self {
+        Self { num_binders, value }
+    }
 }
 
 impl<T: TypeWalk> Binders<T> {
@@ -906,8 +906,7 @@ impl HirDisplay for ApplicationTy {
                 write!(f, ") -> {}", sig.ret().display(f.db))?;
             }
             TypeCtor::FnDef(def) => {
-                let sig = f.db.callable_item_signature(def)
-                    .subst(&self.parameters);
+                let sig = f.db.callable_item_signature(def).subst(&self.parameters);
                 let name = match def {
                     CallableDef::FunctionId(ff) => f.db.function_data(ff).name.clone(),
                     CallableDef::StructId(s) => f.db.struct_data(s).name.clone(),
@@ -1037,17 +1036,19 @@ impl HirDisplay for Ty {
             Ty::Apply(a_ty) => a_ty.hir_fmt(f)?,
             Ty::Projection(p_ty) => p_ty.hir_fmt(f)?,
             Ty::Param(id) => {
-                let generic_params = f.db.generic_params(id.parent);
-                let param_data = &generic_params.types[id.local_id];
+                let generics = generics(f.db, id.parent);
+                let param_data = &generics.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")?
+                        let bounds = f.db.generic_predicates_for_param(*id);
+                        write!(f, "impl ")?;
+                        write_bounds_like_dyn_trait(&bounds, f)?;
                     }
                 }
-            },
+            }
             Ty::Bound(idx) => write!(f, "?{}", idx)?,
             Ty::Dyn(predicates) | Ty::Opaque(predicates) => {
                 match self {
@@ -1055,66 +1056,7 @@ impl HirDisplay for Ty {
                     Ty::Opaque(_) => write!(f, "impl ")?,
                     _ => unreachable!(),
                 };
-                // Note: This code is written to produce nice results (i.e.
-                // corresponding to surface Rust) for types that can occur in
-                // actual Rust. It will have weird results if the predicates
-                // aren't as expected (i.e. self types = $0, projection
-                // predicates for a certain trait come after the Implemented
-                // predicate for that trait).
-                let mut first = true;
-                let mut angle_open = false;
-                for p in predicates.iter() {
-                    match p {
-                        GenericPredicate::Implemented(trait_ref) => {
-                            if angle_open {
-                                write!(f, ">")?;
-                            }
-                            if !first {
-                                write!(f, " + ")?;
-                            }
-                            // We assume that the self type is $0 (i.e. the
-                            // existential) here, which is the only thing that's
-                            // possible in actual Rust, and hence don't print it
-                            write!(f, "{}", f.db.trait_data(trait_ref.trait_).name.clone())?;
-                            if trait_ref.substs.len() > 1 {
-                                write!(f, "<")?;
-                                f.write_joined(&trait_ref.substs[1..], ", ")?;
-                                // there might be assoc type bindings, so we leave the angle brackets open
-                                angle_open = true;
-                            }
-                        }
-                        GenericPredicate::Projection(projection_pred) => {
-                            // in types in actual Rust, these will always come
-                            // after the corresponding Implemented predicate
-                            if angle_open {
-                                write!(f, ", ")?;
-                            } else {
-                                write!(f, "<")?;
-                                angle_open = true;
-                            }
-                            let name =
-                                f.db.type_alias_data(projection_pred.projection_ty.associated_ty)
-                                    .name
-                                    .clone();
-                            write!(f, "{} = ", name)?;
-                            projection_pred.ty.hir_fmt(f)?;
-                        }
-                        GenericPredicate::Error => {
-                            if angle_open {
-                                // impl Trait<X, {error}>
-                                write!(f, ", ")?;
-                            } else if !first {
-                                // impl Trait + {error}
-                                write!(f, " + ")?;
-                            }
-                            p.hir_fmt(f)?;
-                        }
-                    }
-                    first = false;
-                }
-                if angle_open {
-                    write!(f, ">")?;
-                }
+                write_bounds_like_dyn_trait(&predicates, f)?;
             }
             Ty::Unknown => write!(f, "{{unknown}}")?,
             Ty::Infer(..) => write!(f, "_")?,
@@ -1123,6 +1065,71 @@ impl HirDisplay for Ty {
     }
 }
 
+fn write_bounds_like_dyn_trait(
+    predicates: &[GenericPredicate],
+    f: &mut HirFormatter<impl HirDatabase>,
+) -> fmt::Result {
+    // Note: This code is written to produce nice results (i.e.
+    // corresponding to surface Rust) for types that can occur in
+    // actual Rust. It will have weird results if the predicates
+    // aren't as expected (i.e. self types = $0, projection
+    // predicates for a certain trait come after the Implemented
+    // predicate for that trait).
+    let mut first = true;
+    let mut angle_open = false;
+    for p in predicates.iter() {
+        match p {
+            GenericPredicate::Implemented(trait_ref) => {
+                if angle_open {
+                    write!(f, ">")?;
+                }
+                if !first {
+                    write!(f, " + ")?;
+                }
+                // We assume that the self type is $0 (i.e. the
+                // existential) here, which is the only thing that's
+                // possible in actual Rust, and hence don't print it
+                write!(f, "{}", f.db.trait_data(trait_ref.trait_).name.clone())?;
+                if trait_ref.substs.len() > 1 {
+                    write!(f, "<")?;
+                    f.write_joined(&trait_ref.substs[1..], ", ")?;
+                    // there might be assoc type bindings, so we leave the angle brackets open
+                    angle_open = true;
+                }
+            }
+            GenericPredicate::Projection(projection_pred) => {
+                // in types in actual Rust, these will always come
+                // after the corresponding Implemented predicate
+                if angle_open {
+                    write!(f, ", ")?;
+                } else {
+                    write!(f, "<")?;
+                    angle_open = true;
+                }
+                let name =
+                    f.db.type_alias_data(projection_pred.projection_ty.associated_ty).name.clone();
+                write!(f, "{} = ", name)?;
+                projection_pred.ty.hir_fmt(f)?;
+            }
+            GenericPredicate::Error => {
+                if angle_open {
+                    // impl Trait<X, {error}>
+                    write!(f, ", ")?;
+                } else if !first {
+                    // impl Trait + {error}
+                    write!(f, " + ")?;
+                }
+                p.hir_fmt(f)?;
+            }
+        }
+        first = false;
+    }
+    if angle_open {
+        write!(f, ">")?;
+    }
+    Ok(())
+}
+
 impl TraitRef {
     fn hir_fmt_ext(&self, f: &mut HirFormatter<impl HirDatabase>, use_as: bool) -> fmt::Result {
         if f.should_truncate() {
diff --git a/crates/ra_hir_ty/src/lower.rs b/crates/ra_hir_ty/src/lower.rs
index 42367b181..e375c4847 100644
--- a/crates/ra_hir_ty/src/lower.rs
+++ b/crates/ra_hir_ty/src/lower.rs
@@ -10,12 +10,13 @@ use std::sync::Arc;
 
 use hir_def::{
     builtin_type::BuiltinType,
-    generics::{WherePredicate, WherePredicateTarget},
+    generics::{WherePredicate, WherePredicateTarget, TypeParamProvenance},
     path::{GenericArg, Path, PathSegment, PathSegments},
     resolver::{HasResolver, Resolver, TypeNs},
     type_ref::{TypeBound, TypeRef},
     AdtId, ConstId, EnumId, EnumVariantId, FunctionId, GenericDefId, HasModule, ImplId,
     LocalStructFieldId, Lookup, StaticId, StructId, TraitId, TypeAliasId, UnionId, VariantId,
+    TypeParamId
 };
 use ra_arena::map::ArenaMap;
 use ra_db::CrateId;
@@ -30,8 +31,6 @@ use crate::{
     Binders, FnSig, GenericPredicate, PolyFnSig, ProjectionPredicate, ProjectionTy, Substs,
     TraitEnvironment, TraitRef, Ty, TypeCtor,
 };
-use hir_def::TypeParamId;
-use hir_def::generics::TypeParamProvenance;
 
 #[derive(Debug)]
 pub struct TyLoweringContext<'a, DB: HirDatabase> {
diff --git a/crates/ra_hir_ty/src/tests/traits.rs b/crates/ra_hir_ty/src/tests/traits.rs
index e6f697fa3..bae5eae07 100644
--- a/crates/ra_hir_ty/src/tests/traits.rs
+++ b/crates/ra_hir_ty/src/tests/traits.rs
@@ -856,11 +856,11 @@ trait Trait<T> {
     fn foo(&self) -> T;
     fn foo2(&self) -> i64;
 }
-fn bar(impl Trait<u64>) {}
+fn bar(x: impl Trait<u16>) {}
 struct S<T>(T);
 impl<T> Trait<T> for S<T> {}
 
-fn test(x: impl Trait<u64>, y: &impl Trait<u64>) {
+fn test(x: impl Trait<u64>, y: &impl Trait<u32>) {
     x;
     y;
     let z = S(1);
@@ -876,27 +876,32 @@ fn test(x: impl Trait<u64>, y: &impl Trait<u64>) {
         @r###"
     [30; 34) 'self': &Self
     [55; 59) 'self': &Self
-    [99; 101) '{}': ()
-    [111; 112) 'x': impl Trait<u64>
-    [131; 132) 'y': &impl Trait<u64>
-    [152; 269) '{     ...2(); }': ()
-    [158; 159) 'x': impl Trait<u64>
-    [165; 166) 'y': &impl Trait<u64>
-    [176; 177) 'z': impl Trait<u64>
-    [180; 183) 'bar': fn bar() -> impl Trait<u64>
-    [180; 185) 'bar()': impl Trait<u64>
-    [191; 192) 'x': impl Trait<u64>
-    [191; 198) 'x.foo()': u64
-    [204; 205) 'y': &impl Trait<u64>
-    [204; 211) 'y.foo()': u64
-    [217; 218) 'z': impl Trait<u64>
-    [217; 224) 'z.foo()': u64
-    [230; 231) 'x': impl Trait<u64>
-    [230; 238) 'x.foo2()': i64
-    [244; 245) 'y': &impl Trait<u64>
-    [244; 252) 'y.foo2()': i64
-    [258; 259) 'z': impl Trait<u64>
-    [258; 266) 'z.foo2()': i64
+    [78; 79) 'x': impl Trait<u16>
+    [98; 100) '{}': ()
+    [155; 156) 'x': impl Trait<u64>
+    [175; 176) 'y': &impl Trait<u32>
+    [196; 324) '{     ...2(); }': ()
+    [202; 203) 'x': impl Trait<u64>
+    [209; 210) 'y': &impl Trait<u32>
+    [220; 221) 'z': S<u16>
+    [224; 225) 'S': S<u16>(u16) -> S<u16>
+    [224; 228) 'S(1)': S<u16>
+    [226; 227) '1': u16
+    [234; 237) 'bar': fn bar<S<u16>>(S<u16>) -> ()
+    [234; 240) 'bar(z)': ()
+    [238; 239) 'z': S<u16>
+    [246; 247) 'x': impl Trait<u64>
+    [246; 253) 'x.foo()': u64
+    [259; 260) 'y': &impl Trait<u32>
+    [259; 266) 'y.foo()': u32
+    [272; 273) 'z': S<u16>
+    [272; 279) 'z.foo()': u16
+    [285; 286) 'x': impl Trait<u64>
+    [285; 293) 'x.foo2()': i64
+    [299; 300) 'y': &impl Trait<u32>
+    [299; 307) 'y.foo2()': i64
+    [313; 314) 'z': S<u16>
+    [313; 321) 'z.foo2()': i64
     "###
     );
 }