Is DeepQuery missing a HasLink instance?

[saurabhnanda]

Upgraded to servant-server-0.20.2 to specifically use the new DeepQuery feature, however, got the following compilation error upon using it:

/home/vl/vacationlabs/haskell/src/Plugin/ItinerarySegments/Links.hs:13:14-38: error:
    * There is no instance for HasLink (DeepQuery
                                          "search" Models.ItinerarySegment.SearchOpts :> ...)
    * In the expression:
          allFieldLinks' linkToText :: Routes (AsLink Text)
      In a pattern binding:
        Routes {..} = allFieldLinks' linkToText :: Routes (AsLink Text)
   |
13 | Routes{..} = allFieldLinks' linkToText :: Routes (AsLink Text)
   |              ^^^^^^^^^^^^^^^^^^^^^^^^^

[tchoutri]

cc @divarvel

[saurabhnanda]

@tchoutri @divarvel does this look good to raise a PR (except the toS stuff, of course):

instance (KnownSymbol sym, ToDeepQuery record, HasLink sub) => HasLink (DeepQuery sym record :> sub) where
  type MkLink (DeepQuery sym record :> sub) a =
    record -> MkLink sub a

  -- toLink :: (Link -> a) -> Proxy endpoint -> Link -> MkLink endpoint a
  toLink toA _ lnk record =
    toLink toA (Proxy @sub) $ addParams lnk
    where
      k :: Text
      k = toS $ symbolVal (Proxy @sym)

      mkSingleParam x = 
        let (a, b) = generateDeepParam k x
        in SingleParam (toS a) (toS $ escapeURIString isUnreserved $ toS $ fromMaybe "" b)

      addParams lnk = 
        DL.foldl' (\memo x -> addQueryParam (mkSingleParam x) memo) lnk $ 
        toDeepQuery record

Also, why does ToDeepQuery deal with Text when inserting the results into the actual Link would force one to convert them to String?