Don't be so eager to call unresolved inference variables an error. MC

is being used now before the final regionck stage and in some cases SOME
amount of unresolved inference is OK. In fact, we could probably just
allow inference variables as well with only minimal pain.

Author: nikomatsakis

src/librustc/middle/infer/mod.rs

@@ -1162,7 +1162,15 @@ impl<'a, 'tcx> InferCtxt<'a, 'tcx> {
     /// these unconstrained type variables.
     fn resolve_type_vars_or_error(&self, t: &Ty<'tcx>) -> mc::McResult<Ty<'tcx>> {
         let ty = self.resolve_type_vars_if_possible(t);
-        if ty.has_infer_types() || ty.references_error() { Err(()) } else { Ok(ty) }
+        if ty.references_error() {
+            debug!("resolve_type_vars_or_error: error from {:?}", ty);
+            Err(())
+        } else if ty.is_ty_var() {
+            debug!("resolve_type_vars_or_error: error from {:?}", ty);
+            Err(())
+        } else {
+            Ok(ty)
+        }
     }
 
     pub fn fully_resolve<T:TypeFoldable<'tcx>>(&self, value: &T) -> FixupResult<T> {