Do not lose selected value in selectFieldHelper when validation fails

yesod-form/ChangeLog.md

@@ -1,5 +1,10 @@
 # ChangeLog for yesod-form
 
+## Unreleased
+
+* make sure a select field does not lose the selected value even if a validation on the
+  field fails
+
 ## 1.6.2
 
 * Move `addClass` from private/undocumented in `Yesod.Form.Bootstrap3` to `Yesod.Form.Functions` [#1510](https://github.com/yesodweb/yesod/pull/1510)

yesod-form/Yesod/Form/Fields.hs

@@ -759,7 +759,7 @@ selectFieldHelper outside onOpt inside opts' = Field
     , fieldEnctype = UrlEncoded
     }
   where
-    render _ (Left _) = ""
+    render _ (Left x) = x
     render opts (Right a) = maybe "" optionExternalValue $ listToMaybe $ filter ((== a) . optionInternalValue) opts
     selectParser _ [] = Right Nothing
     selectParser opts (s:_) = case s of