Fix #3373

Basically, we need to allow variables in the caller self type to unify with the
impl's declared self type. That requires some more contortions in the variable
handling. I'm looking forward to (hopefully) handling this in a cleaner way when
we switch to Chalk's types and unification code.

1 files changed, 4 insertions, 0 deletions

diff --git a/crates/ra_hir_ty/src/lib.rs b/crates/ra_hir_ty/src/lib.rs
index 0009c426c..ca194f806 100644
--- a/crates/ra_hir_ty/src/lib.rs
+++ b/crates/ra_hir_ty/src/lib.rs
@@ -355,6 +355,10 @@ impl Substs {
         Substs(self.0[..std::cmp::min(self.0.len(), n)].into())
     }
 
+    pub fn suffix(&self, n: usize) -> Substs {
+        Substs(self.0[self.0.len() - std::cmp::min(self.0.len(), n)..].into())
+    }
+
     pub fn as_single(&self) -> &Ty {
         if self.0.len() != 1 {
             panic!("expected substs of len 1, got {:?}", self);