Prepare Elm code generator for use of AuthProtect

Using AuthProtect to implement custom authentication for an API won't work with
servant-elm (see haskell-servant/servant-elm#11).

This change is simlilar to the one suggested in that issue, but rather than
doing nothing, it adds an Authorization header to the request (which results
in another parameter being passed into the generated API request functions
to set the header value). Elm doesn't provide a way to modify the request data
once it has been created so without this it would be impossible to set a
header.

code-generator/Main.hs

@@ -1,14 +1,21 @@
-{-# LANGUAGE FlexibleContexts  #-}
+{-# LANGUAGE FlexibleInstances #-}
+{-# LANGUAGE FlexibleContexts #-}
 {-# LANGUAGE OverloadedStrings #-}
-{-# LANGUAGE TypeOperators     #-}
+{-# LANGUAGE MultiParamTypeClasses #-}
+{-# LANGUAGE TypeFamilies #-}
+{-# LANGUAGE TypeOperators #-}
+{-# LANGUAGE ScopedTypeVariables #-}
 
 module Main where
 
 import           Control.Monad (join)
 import           Data.Monoid ((<>))
-import           Data.Proxy  (Proxy (Proxy))
+import           Data.Proxy (Proxy (Proxy))
+import           Data.Text (Text)
 import           Elm (Spec (Spec), specsToDir, toElmTypeSource, toElmDecoderSource, toElmEncoderSource)
+import           GHC.TypeLits (KnownSymbol)
 import           Servant.Elm (ElmOptions (..), defElmImports, defElmOptions, generateElmForAPIWith, UrlPrefix (Static))
+import           Servant.Foreign hiding (Static)
 
 import           Api.Types
 
@@ -44,5 +51,18 @@ specs =
 
     sourceFor t = [ (toElmTypeSource t, [toElmDecoderSource t, toElmEncoderSource t]) ]
 
+-- Add Authorization header argument to APIs with AuthProtect in them
+instance (KnownSymbol sym, HasForeignType lang ftype Text, HasForeign lang ftype sublayout)
+    => HasForeign lang ftype (AuthProtect sym :> sublayout) where
+    type Foreign ftype (AuthProtect sym :> sublayout) = Foreign ftype sublayout
+
+    foreignFor lang ftype Proxy req = foreignFor lang ftype (Proxy :: Proxy sublayout) req'
+      where
+        req' = req { _reqHeaders = HeaderArg arg : _reqHeaders req }
+        arg = Arg
+            { _argName = PathSegment "Authorization"
+            , _argType = typeFor lang (Proxy :: Proxy ftype) (Proxy :: Proxy Text)
+            }
+
 main :: IO ()
 main = specsToDir specs "frontend/src"

my3ml.cabal

@@ -57,6 +57,7 @@ executable code-generator
                      , my3ml
                      , servant-elm >= 0.4
                      , servant-server >= 0.5
+                     , servant-foreign >= 0.9
                      , text
   default-language:    Haskell2010