From f0532b86f6e23f023e626c49f0a1f93c3f4d043c Mon Sep 17 00:00:00 2001
From: Simon Jakobi <simon.jakobi@gmail.com>
Date: Fri, 19 Jun 2020 02:21:06 +0200
Subject: [PATCH] Silence redundant import warnings for Control.Monad.Fail
 (#633)

Also address mysterious redundant import warnings in the testsuite

This allows us to enable `buildStrictly=true` for GHC 8.8.

Fixes #613.
---
 .travis.yml               | 1 +
 src/Nix/Fresh.hs          | 2 ++
 src/Nix/Fresh/Basic.hs    | 3 +++
 src/Nix/Reduce.hs         | 3 +++
 src/Nix/Render.hs         | 3 +++
 src/Nix/Standard.hs       | 2 ++
 src/Nix/Type/Infer.hs     | 3 +++
 src/Nix/Utils/Fix1.hs     | 3 +++
 tests/PrettyParseTests.hs | 5 +----
 9 files changed, 21 insertions(+), 4 deletions(-)

diff --git a/.travis.yml b/.travis.yml
index f1e2dd8..e6d8ca0 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -101,6 +101,7 @@ jobs:
     - name: GHC 8.8.3, macOS
       env:
         - GHCVERSION=ghc883
+        - buildStrictly=true
       os: osx
     - name: GHC 8.10.1, Linux, SDist, Optimize, Benchmark, Haddock, Shell Completions
       env:
diff --git a/src/Nix/Fresh.hs b/src/Nix/Fresh.hs
index 44654eb..a52e115 100644
--- a/src/Nix/Fresh.hs
+++ b/src/Nix/Fresh.hs
@@ -16,7 +16,9 @@ import           Control.Applicative
 import           Control.Monad.Base
 import           Control.Monad.Catch
 import           Control.Monad.Except
+#if !MIN_VERSION_base(4,13,0)
 import           Control.Monad.Fail
+#endif
 import           Control.Monad.Reader
 import           Control.Monad.Ref
 import           Control.Monad.ST
diff --git a/src/Nix/Fresh/Basic.hs b/src/Nix/Fresh/Basic.hs
index 0ead889..2c0e96e 100644
--- a/src/Nix/Fresh/Basic.hs
+++ b/src/Nix/Fresh/Basic.hs
@@ -1,3 +1,4 @@
+{-# LANGUAGE CPP #-}
 {-# LANGUAGE FlexibleInstances #-}
 {-# LANGUAGE MultiParamTypeClasses #-}
 {-# LANGUAGE ScopedTypeVariables #-}
@@ -8,7 +9,9 @@
 
 module Nix.Fresh.Basic where
 
+#if !MIN_VERSION_base(4,13,0)
 import           Control.Monad.Fail ( MonadFail )
+#endif
 import           Control.Monad.Reader
 import           Nix.Effects
 import           Nix.Render
diff --git a/src/Nix/Reduce.hs b/src/Nix/Reduce.hs
index cf96202..d462bdf 100644
--- a/src/Nix/Reduce.hs
+++ b/src/Nix/Reduce.hs
@@ -1,3 +1,4 @@
+{-# LANGUAGE CPP #-}
 {-# LANGUAGE AllowAmbiguousTypes #-}
 {-# LANGUAGE ApplicativeDo #-}
 {-# LANGUAGE ConstraintKinds #-}
@@ -35,7 +36,9 @@ import           Control.Applicative
 import           Control.Arrow                  ( second )
 import           Control.Monad
 import           Control.Monad.Catch
+#if !MIN_VERSION_base(4,13,0)
 import           Control.Monad.Fail
+#endif
 import           Control.Monad.Fix
 import           Control.Monad.IO.Class
 import           Control.Monad.Reader
diff --git a/src/Nix/Render.hs b/src/Nix/Render.hs
index 8597fd0..127ead9 100644
--- a/src/Nix/Render.hs
+++ b/src/Nix/Render.hs
@@ -1,3 +1,4 @@
+{-# LANGUAGE CPP #-}
 {-# LANGUAGE ConstraintKinds #-}
 {-# LANGUAGE DefaultSignatures #-}
 {-# LANGUAGE FlexibleContexts #-}
@@ -12,7 +13,9 @@ module Nix.Render where
 
 import           Prelude                 hiding ( readFile )
 
+#if !MIN_VERSION_base(4,13,0)
 import           Control.Monad.Fail             ( MonadFail )
+#endif
 import           Control.Monad.Trans
 import           Data.ByteString                ( ByteString )
 import qualified Data.ByteString               as BS
diff --git a/src/Nix/Standard.hs b/src/Nix/Standard.hs
index 624b23d..e3ed3d0 100644
--- a/src/Nix/Standard.hs
+++ b/src/Nix/Standard.hs
@@ -22,7 +22,9 @@ import           Control.Applicative
 import           Control.Comonad                ( Comonad )
 import           Control.Comonad.Env            ( ComonadEnv )
 import           Control.Monad.Catch     hiding ( catchJust )
+#if !MIN_VERSION_base(4,13,0)
 import           Control.Monad.Fail             ( MonadFail )
+#endif
 import           Control.Monad.Free
 import           Control.Monad.Reader
 import           Control.Monad.Ref
diff --git a/src/Nix/Type/Infer.hs b/src/Nix/Type/Infer.hs
index ac2d296..39aa63b 100644
--- a/src/Nix/Type/Infer.hs
+++ b/src/Nix/Type/Infer.hs
@@ -1,3 +1,4 @@
+{-# LANGUAGE CPP #-}
 {-# LANGUAGE AllowAmbiguousTypes #-}
 {-# LANGUAGE ConstraintKinds #-}
 {-# LANGUAGE ExistentialQuantification #-}
@@ -30,7 +31,9 @@ import           Control.Applicative
 import           Control.Arrow
 import           Control.Monad.Catch
 import           Control.Monad.Except
+#if !MIN_VERSION_base(4,13,0)
 import           Control.Monad.Fail
+#endif
 import           Control.Monad.Logic
 import           Control.Monad.Reader
 import           Control.Monad.Ref
diff --git a/src/Nix/Utils/Fix1.hs b/src/Nix/Utils/Fix1.hs
index 8b593b9..8116449 100644
--- a/src/Nix/Utils/Fix1.hs
+++ b/src/Nix/Utils/Fix1.hs
@@ -1,3 +1,4 @@
+{-# LANGUAGE CPP #-}
 {-# LANGUAGE FlexibleInstances #-}
 {-# LANGUAGE GeneralizedNewtypeDeriving #-}
 {-# LANGUAGE MultiParamTypeClasses #-}
@@ -11,7 +12,9 @@ module Nix.Utils.Fix1 where
 
 import           Control.Applicative
 import           Control.Monad
+#if !MIN_VERSION_base(4,13,0)
 import           Control.Monad.Fail
+#endif
 import           Control.Monad.Fix
 import           Control.Monad.IO.Class
 import           Control.Monad.Catch
diff --git a/tests/PrettyParseTests.hs b/tests/PrettyParseTests.hs
index cb5c6a5..94d7b2d 100644
--- a/tests/PrettyParseTests.hs
+++ b/tests/PrettyParseTests.hs
@@ -29,10 +29,7 @@ import           Nix.Parser
 import           Nix.Pretty
 import           Test.Tasty
 import           Test.Tasty.Hedgehog
-import           Text.Megaparsec                ( Pos
-                                                , SourcePos
-                                                , mkPos
-                                                )
+import           Text.Megaparsec                ( Pos )
 import qualified Text.Show.Pretty              as PS
 
 asciiString :: MonadGen m => m String