More trait infrastructure

 - make it possible to get parent trait from method
 - add 'obligation' machinery for checking that a type implements a
   trait (and inferring facts about type variables from that)
 - handle type parameters of traits (to a certain degree)
 - improve the hacky implements check to cover enough cases to exercise the
   handling of traits with type parameters
 - basic canonicalization (will probably also be done by Chalk)

1 files changed, 8 insertions, 1 deletions

diff --git a/crates/ra_hir/src/ty/lower.rs b/crates/ra_hir/src/ty/lower.rs
index 4523b3954..ccacb5e73 100644
--- a/crates/ra_hir/src/ty/lower.rs
+++ b/crates/ra_hir/src/ty/lower.rs
@@ -206,6 +206,7 @@ impl TraitRef {
         db: &impl HirDatabase,
         resolver: &Resolver,
         type_ref: &TypeRef,
+        explicit_self_ty: Option<Ty>,
     ) -> Option<Self> {
         let path = match type_ref {
             TypeRef::Path(path) => path,
@@ -215,7 +216,13 @@ impl TraitRef {
             Resolution::Def(ModuleDef::Trait(tr)) => tr,
             _ => return None,
         };
-        let substs = Self::substs_from_path(db, resolver, path, resolved);
+        let mut substs = Self::substs_from_path(db, resolver, path, resolved);
+        if let Some(self_ty) = explicit_self_ty {
+            // FIXME this could be nicer
+            let mut substs_vec = substs.0.to_vec();
+            substs_vec[0] = self_ty;
+            substs.0 = substs_vec.into();
+        }
         Some(TraitRef { trait_: resolved, substs })
     }