bugfix release v 0.20.1

Web/Scotty/Internal/Types.hs

@@ -1,7 +1,6 @@
 {-# LANGUAGE CPP #-}
 {-# LANGUAGE DeriveDataTypeable #-}
 {-# LANGUAGE DerivingStrategies #-}
-{-# language DerivingVia #-}
 {-# LANGUAGE FlexibleInstances #-}
 {-# LANGUAGE GeneralizedNewtypeDeriving #-}
 {-# LANGUAGE MultiParamTypeClasses #-}
@@ -20,6 +19,7 @@ import qualified Control.Exception as E
 import           Control.Monad (MonadPlus(..))
 import           Control.Monad.Base (MonadBase)
 import           Control.Monad.Catch (MonadCatch, MonadThrow)
+import           Control.Monad.Error.Class (MonadError(..))
 import           Control.Monad.IO.Class (MonadIO(..))
 import UnliftIO (MonadUnliftIO(..))
 import           Control.Monad.Reader (MonadReader(..), ReaderT, asks)
@@ -207,6 +207,15 @@ defaultScottyResponse = SR status200 [] (ContentBuilder mempty)
 
 newtype ActionT m a = ActionT { runAM :: ReaderT ActionEnv m a }
   deriving newtype (Functor, Applicative, Monad, MonadIO, MonadReader ActionEnv, MonadTrans, MonadThrow, MonadCatch, MonadBase b, MonadBaseControl b, MonadTransControl, MonadUnliftIO)
+
+-- | Models the invariant that only 'StatusError's can be thrown and caught.
+instance (MonadUnliftIO m) => MonadError StatusError (ActionT m) where
+  throwError = E.throw
+  catchError = catch
+-- | Modeled after the behaviour in scotty < 0.20, 'fail' throws a 'StatusError' with code 500 ("Server Error"), which can be caught with 'E.catch' or 'rescue'.
+instance (MonadIO m) => MonadFail (ActionT m) where
+  fail = E.throw . StatusError status500 . pack
+-- | 'empty' throws 'ActionError' 'AENext', whereas '(<|>)' catches any 'ActionError's or 'StatusError's in the first action and proceeds to the second one.
 instance (MonadUnliftIO m) => Alternative (ActionT m) where
   empty = E.throw AENext
   a <|> b = do

changelog.md

@@ -1,6 +1,11 @@
 ## next [????.??.??]
 
+## 0.20.1 [2023.10.03]
+
 * remove dependencies on 'base-compat' and 'base-compat-batteries' (#318)
+* re-add MonadFail (ActionT m) instance (#325)
+* re-add MonadError (ActionT m) instance, but the error type is now specialized to 'StatusError' (#325)
+* raise lower bound on base ( > 4.14 ) to reflect support for GHC >= 8.10 (#325).
 
 ## 0.20 [2023.10.02]
 * Drop support for GHC < 8.10 and modernise the CI pipeline (#300).
@@ -14,8 +19,10 @@
 Breaking:
 
 * (#310) Introduce `unliftio` as a dependency, and base exception handling on `catch`.
-** Clarify the exception handling mechanism of ActionT, ScottyT. `rescue` changes signature to use proper `Exception` types rather than strings.
-** All ActionT methods (`text`, `html` etc.) have now a MonadIO constraint on the base monad rather than Monad because the response is constructed in a TVar inside ActionEnv. `rescue` has a MonadUnliftIO constraint. The Alternative instance of ActionT also is based on MonadUnliftIO because `<|>` is implemented in terms of `catch`. `ScottyT` and `ActionT` do not have an exception type parameter anymore.
+* (#310) Clarify the exception handling mechanism of ActionT, ScottyT. `rescue` changes signature to use proper `Exception` types rather than strings. Remove `ScottyError` typeclass.
+* (#310) All ActionT methods (`text`, `html` etc.) have now a MonadIO constraint on the base monad rather than Monad because the response is constructed in a TVar inside ActionEnv. `rescue` has a MonadUnliftIO constraint. The Alternative instance of ActionT also is based on MonadUnliftIO because `<|>` is implemented in terms of `catch`. `ScottyT` and `ActionT` do not have an exception type parameter anymore.
+* (#310) MonadError e (ActionT m) instance removed
+* (#310) MonadFail (ActionT m) instance is missing by mistake.
 
 ## 0.12.1 [2022.11.17]
 * Fix CPP bug that prevented tests from building on Windows.

scotty.cabal

@@ -1,5 +1,5 @@
 Name:                scotty
-Version:             0.20
+Version:             0.20.1
 Synopsis:            Haskell web framework inspired by Ruby's Sinatra, using WAI and Warp
 Homepage:            https://github.com/scotty-web/scotty
 Bug-reports:         https://github.com/scotty-web/scotty/issues
@@ -69,7 +69,7 @@ Library
                        Web.Scotty.Util
   default-language:    Haskell2010
   build-depends:       aeson                 >= 0.6.2.1  && < 2.3,
-                       base                  >= 4.6      && < 5,
+                       base                  >= 4.14     && < 5,
                        blaze-builder         >= 0.3.3.0  && < 0.5,
                        bytestring            >= 0.10.0.2 && < 0.12,
                        case-insensitive      >= 1.0.0.1  && < 1.3,

test/Web/ScottySpec.hs

@@ -141,6 +141,14 @@ spec = do
           get "/dictionary?word2=y" `shouldRespondWith` "y"
           get "/dictionary?word1=a&word2=b" `shouldRespondWith` "a"
 
+    context "MonadFail instance" $ do
+      withApp (Scotty.get "/" $ fail "boom!") $ do
+        it "returns 500 if not caught" $
+          get "/" `shouldRespondWith` 500
+      withApp (Scotty.get "/" $ (fail "boom!") `rescue` (\(_ :: StatusError) -> text "ok")) $
+        it "can catch the StatusError thrown by fail" $ do
+          get "/" `shouldRespondWith` 200 { matchBody = "ok"}
+
     describe "redirect" $ do
       withApp (
         do