Remove redundant calls to resolve_vars_with_obligations

compiler/rustc_hir_typeck/src/coercion.rs

@@ -1037,6 +1037,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
     /// Returns false if the coercion creates any obligations that result in
     /// errors.
     pub fn can_coerce(&self, expr_ty: Ty<'tcx>, target: Ty<'tcx>) -> bool {
+        // FIXME(-Ztrait-solver=next): We need to structurally resolve both types here.
         let source = self.resolve_vars_with_obligations(expr_ty);
         debug!("coercion::can_with_predicates({:?} -> {:?})", source, target);
 

compiler/rustc_hir_typeck/src/demand.rs

@@ -260,7 +260,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         ));
         let expr = expr.peel_drop_temps();
         let cause = self.misc(expr.span);
-        let expr_ty = self.resolve_vars_with_obligations(checked_ty);
+        let expr_ty = self.resolve_vars_if_possible(checked_ty);
         let mut err = self.err_ctxt().report_mismatched_types(&cause, expected, expr_ty, e);
 
         let is_insufficiently_polymorphic =

compiler/rustc_hir_typeck/src/fn_ctxt/suggestions.rs

@@ -950,7 +950,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         if !expected.is_unit() {
             return;
         }
-        let found = self.resolve_vars_with_obligations(found);
+        let found = self.resolve_vars_if_possible(found);
 
         let in_loop = self.is_loop(id)
             || self

compiler/rustc_hir_typeck/src/method/suggest.rs

@@ -2994,7 +2994,7 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         // This occurs for UFCS desugaring of `T::method`, where there is no
         // receiver expression for the method call, and thus no autoderef.
         if let SelfSource::QPath(_) = source {
-            return is_local(self.resolve_vars_with_obligations(rcvr_ty));
+            return is_local(rcvr_ty);
         }
 
         self.autoderef(span, rcvr_ty).any(|(ty, _)| is_local(ty))