Structurally resolve in only_has_type

FIXME: the span is scuffed

compiler/rustc_hir_typeck/src/expectation.rs

@@ -1,5 +1,5 @@
 use rustc_middle::ty::{self, Ty};
-use rustc_span::Span;
+use rustc_span::{DUMMY_SP, Span};
 
 use super::Expectation::*;
 use super::FnCtxt;
@@ -102,7 +102,7 @@ impl<'a, 'tcx> Expectation<'tcx> {
     /// such a constraint, if it exists.
     pub(super) fn only_has_type(self, fcx: &FnCtxt<'a, 'tcx>) -> Option<Ty<'tcx>> {
         match self {
-            ExpectHasType(ty) => Some(fcx.resolve_vars_if_possible(ty)),
+            ExpectHasType(ty) => Some(fcx.try_structurally_resolve_type(DUMMY_SP, ty)),
             NoExpectation | ExpectCastableToType(_) | ExpectRvalueLikeUnsized(_) => None,
         }
     }