Suggest dereferencing boolean reference when used in 'if' or 'while'

Change-Id: I0c5c4d767be2647e6f017ae7bf83558c56dbca97

Author: XiangQingW

src/librustc_typeck/check/demand.rs

@@ -349,7 +349,11 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
 
         // If the span is from a macro, then it's hard to extract the text
         // and make a good suggestion, so don't bother.
-        let is_macro = sp.from_expansion();
+        let is_desugaring = match sp.desugaring_kind() {
+            Some(k) => sp.is_desugaring(k),
+            None => false
+        };
+        let is_macro = sp.from_expansion() && !is_desugaring;
 
         match (&expr.kind, &expected.kind, &checked_ty.kind) {
             (_, &ty::Ref(_, exp, _), &ty::Ref(_, check, _)) => match (&exp.kind, &check.kind) {

src/librustc_typeck/check/expr.rs

@@ -87,6 +87,8 @@ impl<'a, 'tcx> FnCtxt<'a, 'tcx> {
         }
 
         if let Some(mut err) = self.demand_suptype_diag(expr.span, expected_ty, ty) {
+            self.suggest_ref_or_into(&mut err, expr, expected_ty, ty);
+
             let expr = match &expr.kind {
                 ExprKind::DropTemps(expr) => expr,
                 _ => expr,