Code generation with generateLambdaDispatcher leads to warnings (Update: Addressed by upcoming 4.0.0)

[andys8]

With

generateLambdaDispatcher UseWithAPIGateway defaultDispatcherOptions

I'm currently seeing these warnings:

/app/Main.hs:58:1: warning: [-Wunused-matches]
    Defined but not used: ‘executionUuid’
   |
58 | generateLambdaDispatcher UseWithAPIGateway defaultDispatcherOptions
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

/app/Main.hs:58:1: warning: [-Wunused-matches]
    Defined but not used: ‘eventObject’
   |
58 | generateLambdaDispatcher UseWithAPIGateway defaultDispatcherOptions
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

/app/Main.hs:58:1: warning: [-Wunused-matches]
    Defined but not used: ‘contextObject’
   |
58 | generateLambdaDispatcher UseWithAPIGateway defaultDispatcherOptions
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

/app/Main.hs:58:1: warning: [-Wmissing-signatures]
    Top-level binding with no type signature:
      run :: Applicative f =>
             LambdaOptions context
             -> f (Either
                     aws-lambda-haskell-runtime-3.0.1:Aws.Lambda.Runtime.Common.LambdaError
                     b)
   |
58 | generateLambdaDispatcher UseWithAPIGateway defaultDispatcherOptions
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

/app/Main.hs:58:1: warning: [-Wmissing-signatures]
    Top-level binding with no type signature: main :: IO ()
   |
58 | generateLambdaDispatcher UseWithAPIGateway defaultDispatcherOptions
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Is it possible to get rid of them?

Version 3.0.1

[andys8]

Okay, I think the actual issue, is that the handler function is not picked up and the generated code looks like tihs:

app/Main.hs:62:1-67: Splicing declarations
    generateLambdaDispatcher UseWithAPIGateway defaultDispatcherOptions
  ======>
    main = (runLambda initializeContext) run
    run
      LambdaOptions {functionHandler = functionHandler,
                     contextObject = contextObject, eventObject = eventObject,
                     executionUuid = executionUuid}
      = case functionHandler of {
          _ -> ((pure
                   . (Left
                        . (aws-lambda-haskell-runtime-3.0.1:Aws.Lambda.Runtime.Common.ApiGatewayLambdaError
                             . (mkApiGatewayResponse 500 . toApiGatewayResponseBody))))
                  $ ("Handler "
                       <> (functionHandler <> " does not exist on project"))) }

Will look into it

[andys8]

I tried to inline the generated code, but it looks like that's not possible because ApiGatewayLambdaError is not exposed.

aws-lambda-haskell-runtime/src/Aws/Lambda/Runtime/Common.hs

Line 77 in 8aea720

ApiGatewayLambdaError (ApiGatewayResponse ApiGatewayResponseBody)

[andys8]

This (minimal) apigateway example:

initializeContext :: IO ()
initializeContext = return ()

handler
  :: ApiGatewayRequest Text
  -> Context ()
  -> IO (Either (ApiGatewayResponse Text) (ApiGatewayResponse Text))
handler request context = return $ Right $ mkApiGatewayResponse 200 "OK"

generateLambdaDispatcher UseWithAPIGateway defaultDispatcherOptions

results in:

    main = (runLambda initializeContext) run
    run
      LambdaOptions {functionHandler = functionHandler,
                     contextObject = contextObject, eventObject = eventObject,
                     executionUuid = executionUuid}
      = case functionHandler of {
          _ -> ((pure
                   . (Left
                        . (aws-lambda-haskell-runtime-3.0.1:Aws.Lambda.Runtime.Common.ApiGatewayLambdaError
                             . (mkApiGatewayResponse 500 . toApiGatewayResponseBody))))
                  $ ("Handler "
                       <> (functionHandler <> " does not exist on project"))) }

[andys8]

Okay, I think the issue might actually be, that the formatting of the type signature is in multiple lines. The project is formatted with brittany and :: is not in the same line as handler. Because of this, it won't be picked up!

aws-lambda-haskell-runtime/src/Aws/Lambda/Meta/Discover.hs

Line 65 in 1eda275

& filter (Text.isPrefixOf "handler :: " . Text.pack)

Formatting it like this, is working.

type Req = ApiGatewayRequest Text
type Res = ApiGatewayResponse Text

handler :: Req -> Context () -> IO (Either Res Res)
handler request context = return $ Right $ mkApiGatewayResponse 200 "OK"

[andys8]

With the handler being recognized there are less warnings:

/app/app/Main.hs:68:1: error: [-Wunused-matches, -Werror=unused-matches]
    Defined but not used: ‘executionUuid’
   |
68 | generateLambdaDispatcher UseWithAPIGateway defaultDispatcherOptions
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

/app/app/Main.hs:68:1: error: [-Wmissing-signatures, -Werror=missing-signatures]
    Top-level binding with no type signature:
      run :: LambdaOptions Token.Handle
             -> IO
                  (Either
                     aws-lambda-haskell-runtime-3.0.1:Aws.Lambda.Runtime.Common.LambdaError
                     LambdaResult)
   |
68 | generateLambdaDispatcher UseWithAPIGateway defaultDispatcherOptions
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

/app/app/Main.hs:68:1: error: [-Wmissing-signatures, -Werror=missing-signatures]
    Top-level binding with no type signature: main :: IO ()
   |
68 | generateLambdaDispatcher UseWithAPIGateway defaultDispatcherOptions
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Sorry for spamming comments :)

[NickSeagull]

Hey! Thanks so much for writing such a detailed issue!

I'm currently working on #81 so all Template Haskell code will go away, and with it, all the warnings :)

[andys8]

Nice. I had a look at the changes, and it looks like the search for "handler ::" will also be removed, and therefore a fix is probably not necessary.

I'd leave this issue open for documentation and close it with the rel are of 4.0.0. Looking forward to it.