3 files changed, 64 insertions, 1 deletions

diff --git a/crates/ra_hir_ty/src/infer.rs b/crates/ra_hir_ty/src/infer.rs
index f7ef09f0e..0d65984ee 100644
--- a/crates/ra_hir_ty/src/infer.rs
+++ b/crates/ra_hir_ty/src/infer.rs
@@ -480,7 +480,7 @@ 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::Opaque);
+            let ty = self.make_ty_with_mode(type_ref, ImplTraitLoweringMode::Param);
 
             self.infer_pat(*pat, &ty, BindingMode::default());
         }
diff --git a/crates/ra_hir_ty/src/lower.rs b/crates/ra_hir_ty/src/lower.rs
index 5138019c7..88d962b47 100644
--- a/crates/ra_hir_ty/src/lower.rs
+++ b/crates/ra_hir_ty/src/lower.rs
@@ -30,6 +30,7 @@ use crate::{
     Binders, FnSig, GenericPredicate, PolyFnSig, ProjectionPredicate, ProjectionTy, Substs,
     TraitEnvironment, TraitRef, Ty, TypeCtor,
 };
+use hir_expand::name::Name;
 
 #[derive(Debug)]
 pub struct TyLoweringContext<'a, DB: HirDatabase> {
@@ -69,6 +70,10 @@ pub enum ImplTraitLoweringMode {
     /// i.e. for arguments of the function we're currently checking, and return
     /// types of functions we're calling.
     Opaque,
+    /// `impl Trait` gets lowered into a type variable. Used for argument
+    /// position impl Trait currently, since it allows us to support that
+    /// without Chalk.
+    Param,
     /// `impl Trait` gets lowered into a variable that can unify with some
     /// type. This is used in places where values flow 'in', i.e. for arguments
     /// of functions we're calling, and the return type of the function we're
@@ -137,6 +142,11 @@ impl Ty {
                             .collect();
                         Ty::Opaque(predicates)
                     }
+                    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() }
+                    }
                     ImplTraitLoweringMode::Variable => {
                         let idx = ctx.impl_trait_counter.get();
                         ctx.impl_trait_counter.set(idx + 1);
diff --git a/crates/ra_hir_ty/src/tests/traits.rs b/crates/ra_hir_ty/src/tests/traits.rs
index e2351ca98..dc78e83cd 100644
--- a/crates/ra_hir_ty/src/tests/traits.rs
+++ b/crates/ra_hir_ty/src/tests/traits.rs
@@ -850,6 +850,59 @@ fn test<T: ApplyL>(t: T) {
 }
 
 #[test]
+fn argument_impl_trait() {
+    assert_snapshot!(
+        infer_with_mismatches(r#"
+trait Trait<T> {
+    fn foo(&self) -> T;
+    fn foo2(&self) -> i64;
+}
+fn bar(impl Trait<u64>) {}
+struct S<T>(T);
+impl<T> Trait<T> for S<T> {}
+
+fn test(x: impl Trait<u64>, y: &impl Trait<u64>) {
+    x;
+    y;
+    let z = S(1);
+    bar(z);
+    x.foo();
+    y.foo();
+    z.foo();
+    x.foo2();
+    y.foo2();
+    z.foo2();
+}
+"#, true),
+        @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
+    "###
+    );
+}
+
+#[test]
 #[ignore]
 fn impl_trait() {
     assert_snapshot!(