omitNothingFields is broken

[akhra]

data Foo = Foo { bar :: Maybe Int } deriving Show
$(deriveJSON defaultOptions{omitNothingFields=True} ''Foo)

Error: Couldn't match expected type `Text' with actual type `Builder'
In the first argument of `(.=)', namely `text (pack "bar")'
In the first argument of `(<$>)', namely `(text (pack "bar") .=)'

Maybe fallout related to #287? But here's the weird thing, I actually discovered this first:

type Synonym = Maybe Int
data Foo = Foo { bar :: Synonym } deriving Show
$(deriveJSON defaultOptions{omitNothingFields=True} ''Foo)

>>> decode "{}" :: Maybe Foo
Just (Foo {bar = Nothing})
>>> encode $ Foo Nothing
"{\"bar\":null}"

omitNothingFields wasn't omitting them. I removed the type for sanity checking, and it exploded! (I was working with more complex types, but this simple example shows the same behavior.) So this might be two bugs; for some reason a synonym prevents the compile failure, but still has wrong behavior.

Everything works fine when omitNothingFields=False.

[basvandijk]

The Couldn't match expected type 'Text' with actual type 'Builder' error is a duplicate of #293 which is fixed in HEAD.

I will look into why Nothing fields aren't omitted in:

encode $ Foo Nothing
"{\"bar\":null}"

[bergmark]

Nothing fields are omitted on master so I'll close this.

λ> encode $ Foo Nothing
"{}"