From 9bdecdcb1949b728818cc0312d625f17c8588b0a Mon Sep 17 00:00:00 2001
From: Rodrigo Mesquita <rodrigo.m.mesquita@gmail.com>
Date: Tue, 16 Jan 2024 12:50:03 +0000
Subject: [PATCH] Use ReaderT instead of DerivingVia because of ghc 8.4

---
 Cabal/src/Distribution/Simple/Build/Monad.hs | 15 +++++++++++----
 1 file changed, 11 insertions(+), 4 deletions(-)

diff --git a/Cabal/src/Distribution/Simple/Build/Monad.hs b/Cabal/src/Distribution/Simple/Build/Monad.hs
index 7aab514dfdf..e40232b689a 100644
--- a/Cabal/src/Distribution/Simple/Build/Monad.hs
+++ b/Cabal/src/Distribution/Simple/Build/Monad.hs
@@ -1,8 +1,9 @@
-{-# LANGUAGE DerivingVia #-}
 {-# LANGUAGE NamedFieldPuns #-}
+{-# LANGUAGE PatternSynonyms #-}
+{-# LANGUAGE GeneralizedNewtypeDeriving #-}
 
 module Distribution.Simple.Build.Monad
-  ( BuildM (..)
+  ( BuildM (BuildM)
   , runBuildM
   , PreBuildComponentInputs (..)
 
@@ -49,8 +50,14 @@ data PreBuildComponentInputs = PreBuildComponentInputs
   }
 
 -- | Computations carried out in the context of building a component (e.g. @'buildAllExtraSources'@)
-newtype BuildM a = BuildM (PreBuildComponentInputs -> IO a)
-  deriving (Functor, Applicative, Monad, MonadReader PreBuildComponentInputs, MonadIO) via ReaderT PreBuildComponentInputs IO
+newtype BuildM a = BuildM' (ReaderT PreBuildComponentInputs IO a)
+  deriving (Functor, Applicative, Monad, MonadReader PreBuildComponentInputs, MonadIO)
+-- Ideally we'd use deriving via ReaderT PreBuildComponentInputs IO, but ghc 8.4 doesn't support it.
+
+-- | Construct a t'BuildM' action from an IO function on 'PreBuildComponentInputs'.
+pattern BuildM :: (PreBuildComponentInputs -> IO a) -> BuildM a
+pattern BuildM f = BuildM' (ReaderT f)
+{-# COMPLETE BuildM #-}
 
 -- | Run a 'BuildM' action, i.e. a computation in the context of building a component.
 runBuildM :: BuildingWhat -> LocalBuildInfo -> TargetInfo -> BuildM a -> IO a