Handle impl/dyn Trait in method resolution

When we have one of these, the `Trait` doesn't need to be in scope to call its
methods. So we need to consider this when looking for method
candidates. (Actually I think the same is true when we have a bound `T:
some::Trait`, but we don't handle that yet).

At the same time, since Chalk doesn't handle these types yet, add a small hack
to skip Chalk in method resolution and just consider `impl Trait: Trait` always
true. This is enough to e.g. get completions for `impl Trait`, but since we
don't do any unification we won't infer the return type of e.g. `impl
Into<i64>::into()`.

1 files changed, 13 insertions, 0 deletions

diff --git a/crates/ra_hir/src/ty.rs b/crates/ra_hir/src/ty.rs
index 4e5bdbae4..b54c80318 100644
--- a/crates/ra_hir/src/ty.rs
+++ b/crates/ra_hir/src/ty.rs
@@ -583,6 +583,19 @@ impl Ty {
             ty => ty,
         })
     }
+
+    /// If this is an `impl Trait` or `dyn Trait`, returns that trait.
+    pub fn inherent_trait(&self) -> Option<Trait> {
+        match self {
+            Ty::Dyn(predicates) | Ty::Opaque(predicates) => {
+                predicates.iter().find_map(|pred| match pred {
+                    GenericPredicate::Implemented(tr) => Some(tr.trait_),
+                    _ => None,
+                })
+            }
+            _ => None,
+        }
+    }
 }
 
 impl HirDisplay for &Ty {