3 files changed, 65 insertions, 5 deletions

diff --git a/crates/ra_hir_ty/src/infer/coerce.rs b/crates/ra_hir_ty/src/infer/coerce.rs
index 959b1e212..89200255a 100644
--- a/crates/ra_hir_ty/src/infer/coerce.rs
+++ b/crates/ra_hir_ty/src/infer/coerce.rs
@@ -51,7 +51,7 @@ impl<'a> InferenceContext<'a> {
             // Trivial cases, this should go after `never` check to
             // avoid infer result type to be never
             _ => {
-                if self.table.unify_inner_trivial(&from_ty, &to_ty) {
+                if self.table.unify_inner_trivial(&from_ty, &to_ty, 0) {
                     return true;
                 }
             }
@@ -175,7 +175,7 @@ impl<'a> InferenceContext<'a> {
                     return self.table.unify_substs(st1, st2, 0);
                 }
                 _ => {
-                    if self.table.unify_inner_trivial(&derefed_ty, &to_ty) {
+                    if self.table.unify_inner_trivial(&derefed_ty, &to_ty, 0) {
                         return true;
                     }
                 }
diff --git a/crates/ra_hir_ty/src/infer/unify.rs b/crates/ra_hir_ty/src/infer/unify.rs
index 5f6cea8d3..ab0bc8b70 100644
--- a/crates/ra_hir_ty/src/infer/unify.rs
+++ b/crates/ra_hir_ty/src/infer/unify.rs
@@ -8,7 +8,8 @@ use test_utils::tested_by;
 
 use super::{InferenceContext, Obligation};
 use crate::{
-    BoundVar, Canonical, DebruijnIndex, InEnvironment, InferTy, Substs, Ty, TypeCtor, TypeWalk,
+    BoundVar, Canonical, DebruijnIndex, GenericPredicate, InEnvironment, InferTy, Substs, Ty,
+    TypeCtor, TypeWalk,
 };
 
 impl<'a> InferenceContext<'a> {
@@ -226,16 +227,26 @@ impl InferenceTable {
             (Ty::Apply(a_ty1), Ty::Apply(a_ty2)) if a_ty1.ctor == a_ty2.ctor => {
                 self.unify_substs(&a_ty1.parameters, &a_ty2.parameters, depth + 1)
             }
-            _ => self.unify_inner_trivial(&ty1, &ty2),
+
+            _ => self.unify_inner_trivial(&ty1, &ty2, depth),
         }
     }
 
-    pub(super) fn unify_inner_trivial(&mut self, ty1: &Ty, ty2: &Ty) -> bool {
+    pub(super) fn unify_inner_trivial(&mut self, ty1: &Ty, ty2: &Ty, depth: usize) -> bool {
         match (ty1, ty2) {
             (Ty::Unknown, _) | (_, Ty::Unknown) => true,
 
             (Ty::Placeholder(p1), Ty::Placeholder(p2)) if *p1 == *p2 => true,
 
+            (Ty::Dyn(dyn1), Ty::Dyn(dyn2)) if dyn1.len() == dyn2.len() => {
+                for (pred1, pred2) in dyn1.iter().zip(dyn2.iter()) {
+                    if !self.unify_preds(pred1, pred2, depth + 1) {
+                        return false;
+                    }
+                }
+                true
+            }
+
             (Ty::Infer(InferTy::TypeVar(tv1)), Ty::Infer(InferTy::TypeVar(tv2)))
             | (Ty::Infer(InferTy::IntVar(tv1)), Ty::Infer(InferTy::IntVar(tv2)))
             | (Ty::Infer(InferTy::FloatVar(tv1)), Ty::Infer(InferTy::FloatVar(tv2)))
@@ -268,6 +279,31 @@ impl InferenceTable {
         }
     }
 
+    fn unify_preds(
+        &mut self,
+        pred1: &GenericPredicate,
+        pred2: &GenericPredicate,
+        depth: usize,
+    ) -> bool {
+        match (pred1, pred2) {
+            (GenericPredicate::Implemented(tr1), GenericPredicate::Implemented(tr2))
+                if tr1.trait_ == tr2.trait_ =>
+            {
+                self.unify_substs(&tr1.substs, &tr2.substs, depth + 1)
+            }
+            (GenericPredicate::Projection(proj1), GenericPredicate::Projection(proj2))
+                if proj1.projection_ty.associated_ty == proj2.projection_ty.associated_ty =>
+            {
+                self.unify_substs(
+                    &proj1.projection_ty.parameters,
+                    &proj2.projection_ty.parameters,
+                    depth + 1,
+                ) && self.unify_inner(&proj1.ty, &proj2.ty, depth + 1)
+            }
+            _ => false,
+        }
+    }
+
     /// If `ty` is a type variable with known type, returns that type;
     /// otherwise, return ty.
     pub fn resolve_ty_shallow<'b>(&mut self, ty: &'b Ty) -> Cow<'b, Ty> {
diff --git a/crates/ra_hir_ty/src/tests/traits.rs b/crates/ra_hir_ty/src/tests/traits.rs
index dc517fc4a..f6e3e07cd 100644
--- a/crates/ra_hir_ty/src/tests/traits.rs
+++ b/crates/ra_hir_ty/src/tests/traits.rs
@@ -2378,3 +2378,27 @@ fn main() {
     );
     assert_eq!(t, "Foo");
 }
+
+#[test]
+fn trait_object_no_coercion() {
+    assert_snapshot!(
+        infer_with_mismatches(r#"
+trait Foo {}
+
+fn foo(x: &dyn Foo) {}
+
+fn test(x: &dyn Foo) {
+    foo(x);
+}
+"#, true),
+        @r###"
+    [22; 23) 'x': &dyn Foo
+    [35; 37) '{}': ()
+    [47; 48) 'x': &dyn Foo
+    [60; 75) '{     foo(x); }': ()
+    [66; 69) 'foo': fn foo(&dyn Foo)
+    [66; 72) 'foo(x)': ()
+    [70; 71) 'x': &dyn Foo
+    "###
+    );
+}