Add compiler linting to CI

This commit adds the `lint:compiler` Hadrian target to the CI runner.
It does also fixes hints in the compiler/ and libraries/base/ codebases.

22 files changed, 71 insertions, 84 deletions

diff --git a/compiler/GHC/CmmToAsm.hs b/compiler/GHC/CmmToAsm.hs
index d331d63098..6712db8d05 100644
--- a/compiler/GHC/CmmToAsm.hs
+++ b/compiler/GHC/CmmToAsm.hs
@@ -5,13 +5,16 @@
 --
 -- -----------------------------------------------------------------------------
 
-{-# LANGUAGE BangPatterns, CPP, GADTs, ScopedTypeVariables, PatternSynonyms,
-    DeriveFunctor #-}
-{-# LANGUAGE MultiParamTypeClasses #-}
-{-# LANGUAGE FlexibleInstances #-}
+{-# LANGUAGE BangPatterns #-}
+{-# LANGUAGE CPP #-}
+{-# LANGUAGE DeriveFunctor #-}
 {-# LANGUAGE FlexibleContexts #-}
-{-# LANGUAGE UnboxedTuples #-}
+{-# LANGUAGE FlexibleInstances #-}
+{-# LANGUAGE GADTs #-}
+{-# LANGUAGE MultiParamTypeClasses #-}
+{-# LANGUAGE PatternSynonyms #-}
 {-# LANGUAGE ScopedTypeVariables #-}
+{-# LANGUAGE UnboxedTuples #-}
 
 {-# OPTIONS_GHC -Wno-incomplete-record-updates #-}
 
diff --git a/compiler/GHC/Core/Opt/ConstantFold.hs b/compiler/GHC/Core/Opt/ConstantFold.hs
index c34996b507..3a397330d7 100644
--- a/compiler/GHC/Core/Opt/ConstantFold.hs
+++ b/compiler/GHC/Core/Opt/ConstantFold.hs
@@ -10,8 +10,8 @@ ToDo:
    (i1 + i2) only if it results in a valid Float.
 -}
 
-{-# LANGUAGE CPP #-}
 {-# LANGUAGE AllowAmbiguousTypes #-}
+{-# LANGUAGE CPP #-}
 {-# LANGUAGE DeriveFunctor #-}
 {-# LANGUAGE LambdaCase #-}
 {-# LANGUAGE MultiWayIf #-}
diff --git a/compiler/GHC/Core/Opt/Simplify/Monad.hs b/compiler/GHC/Core/Opt/Simplify/Monad.hs
index 9f95297924..1705cd878f 100644
--- a/compiler/GHC/Core/Opt/Simplify/Monad.hs
+++ b/compiler/GHC/Core/Opt/Simplify/Monad.hs
@@ -5,7 +5,6 @@
 \section[GHC.Core.Opt.Simplify.Monad]{The simplifier Monad}
 -}
 
-{-# LANGUAGE DeriveFunctor #-}
 module GHC.Core.Opt.Simplify.Monad (
         -- The monad
         SimplM,
diff --git a/compiler/GHC/Core/Opt/SpecConstr.hs b/compiler/GHC/Core/Opt/SpecConstr.hs
index 1e00e4cc21..4beed6d061 100644
--- a/compiler/GHC/Core/Opt/SpecConstr.hs
+++ b/compiler/GHC/Core/Opt/SpecConstr.hs
@@ -36,7 +36,7 @@ import GHC.Core.DataCon
 import GHC.Core.Coercion hiding( substCo )
 import GHC.Core.Rules
 import GHC.Core.Type     hiding ( substTy )
-import GHC.Core.TyCon   ( tyConUnique, tyConName )
+import GHC.Core.TyCon   (TyCon, tyConUnique, tyConName )
 import GHC.Core.Multiplicity
 import GHC.Types.Id
 import GHC.Core.Ppr     ( pprParendExpr )
@@ -65,7 +65,6 @@ import Control.Monad    ( zipWithM )
 import Data.List (nubBy, sortBy, partition)
 import GHC.Builtin.Names ( specTyConKey )
 import GHC.Unit.Module
-import GHC.Core.TyCon ( TyCon )
 import GHC.Exts( SpecConstrAnnotation(..) )
 import Data.Ord( comparing )
 
diff --git a/compiler/GHC/Core/TyCo/Rep.hs b/compiler/GHC/Core/TyCo/Rep.hs
index 636dc87405..aa5423d0f6 100644
--- a/compiler/GHC/Core/TyCo/Rep.hs
+++ b/compiler/GHC/Core/TyCo/Rep.hs
@@ -1,6 +1,5 @@
 {-# LANGUAGE CPP                #-}
 {-# LANGUAGE DeriveDataTypeable #-}
-{-# LANGUAGE MultiWayIf         #-}
 
 {-# OPTIONS_HADDOCK not-home #-}
 
diff --git a/compiler/GHC/Data/IOEnv.hs b/compiler/GHC/Data/IOEnv.hs
index 90a2915eac..5a3c56db3f 100644
--- a/compiler/GHC/Data/IOEnv.hs
+++ b/compiler/GHC/Data/IOEnv.hs
@@ -1,5 +1,4 @@
 {-# LANGUAGE CPP #-}
-{-# LANGUAGE DeriveFunctor #-}
 {-# LANGUAGE DerivingVia #-}
 {-# LANGUAGE PatternSynonyms #-}
 --
diff --git a/compiler/GHC/Data/Stream.hs b/compiler/GHC/Data/Stream.hs
index 4e2bee4311..10f12c4462 100644
--- a/compiler/GHC/Data/Stream.hs
+++ b/compiler/GHC/Data/Stream.hs
@@ -1,6 +1,5 @@
 {-# LANGUAGE FlexibleInstances #-}
 {-# LANGUAGE RankNTypes #-}
-{-# LANGUAGE TupleSections #-}
 -- -----------------------------------------------------------------------------
 --
 -- (c) The University of Glasgow 2012
diff --git a/compiler/GHC/Driver/Main.hs b/compiler/GHC/Driver/Main.hs
index c61ae00b55..c060f69c87 100644
--- a/compiler/GHC/Driver/Main.hs
+++ b/compiler/GHC/Driver/Main.hs
@@ -1,8 +1,7 @@
-{-# LANGUAGE CPP                      #-}
-{-# LANGUAGE BangPatterns             #-}
+{-# LANGUAGE BangPatterns #-}
+{-# LANGUAGE CPP #-}
 {-# LANGUAGE NondecreasingIndentation #-}
-{-# LANGUAGE LambdaCase               #-}
-{-# LANGUAGE ViewPatterns             #-}
+
 {-# OPTIONS_GHC -fprof-auto-top #-}
 
 -------------------------------------------------------------------------------
diff --git a/compiler/GHC/Hs/Binds.hs b/compiler/GHC/Hs/Binds.hs
index 34fc3dc3bb..6383eb01b8 100644
--- a/compiler/GHC/Hs/Binds.hs
+++ b/compiler/GHC/Hs/Binds.hs
@@ -8,7 +8,6 @@
 {-# LANGUAGE TypeFamilies #-}
 {-# LANGUAGE UndecidableInstances #-} -- Wrinkle in Note [Trees That Grow]
                                       -- in module Language.Haskell.Syntax.Extension
-{-# LANGUAGE ViewPatterns #-}
 
 {-# OPTIONS_GHC -Wno-orphans #-} -- Outputable
 
diff --git a/compiler/GHC/Hs/Decls.hs b/compiler/GHC/Hs/Decls.hs
index 7592926f07..e5e64267bf 100644
--- a/compiler/GHC/Hs/Decls.hs
+++ b/compiler/GHC/Hs/Decls.hs
@@ -1,17 +1,15 @@
-{-# LANGUAGE CPP                 #-}
-{-# LANGUAGE ConstraintKinds     #-}
-{-# LANGUAGE DeriveDataTypeable  #-}
-{-# LANGUAGE DeriveTraversable   #-}
-{-# LANGUAGE FlexibleContexts    #-}
-{-# LANGUAGE FlexibleInstances   #-}
+{-# LANGUAGE CPP #-}
+{-# LANGUAGE ConstraintKinds #-}
+{-# LANGUAGE DeriveDataTypeable #-}
+{-# LANGUAGE FlexibleContexts #-}
+{-# LANGUAGE FlexibleInstances #-}
 {-# LANGUAGE ScopedTypeVariables #-}
-{-# LANGUAGE StandaloneDeriving  #-}
-{-# LANGUAGE TypeApplications    #-}
-{-# LANGUAGE TypeFamilies        #-}
+{-# LANGUAGE TypeApplications #-}
+{-# LANGUAGE TypeFamilies #-}
 {-# LANGUAGE UndecidableInstances #-} -- Wrinkle in Note [Trees That Grow]
                                       -- in module Language.Haskell.Syntax.Extension
 
-{-# OPTIONS_GHC -Wno-orphans     #-} -- Outputable
+{-# OPTIONS_GHC -Wno-orphans #-} -- Outputable
 
 {-
 (c) The University of Glasgow 2006
diff --git a/compiler/GHC/Hs/Pat.hs b/compiler/GHC/Hs/Pat.hs
index f6ae038745..c5cd2ccb78 100644
--- a/compiler/GHC/Hs/Pat.hs
+++ b/compiler/GHC/Hs/Pat.hs
@@ -1,17 +1,14 @@
-
-{-# LANGUAGE CPP                  #-}
-{-# LANGUAGE ConstraintKinds      #-}
-{-# LANGUAGE DeriveDataTypeable   #-}
-{-# LANGUAGE DeriveTraversable    #-}
-{-# LANGUAGE FlexibleContexts     #-}
-{-# LANGUAGE FlexibleInstances    #-}
-{-# LANGUAGE LambdaCase           #-}
-{-# LANGUAGE ScopedTypeVariables  #-}
-{-# LANGUAGE TypeApplications     #-}
-{-# LANGUAGE TypeFamilies         #-}
+{-# LANGUAGE CPP #-}
+{-# LANGUAGE ConstraintKinds #-}
+{-# LANGUAGE DeriveDataTypeable #-}
+{-# LANGUAGE FlexibleContexts #-}
+{-# LANGUAGE FlexibleInstances #-}
+{-# LANGUAGE LambdaCase #-}
+{-# LANGUAGE ScopedTypeVariables #-}
+{-# LANGUAGE TypeApplications #-}
+{-# LANGUAGE TypeFamilies #-}
 {-# LANGUAGE UndecidableInstances #-} -- Wrinkle in Note [Trees That Grow]
                                       -- in module Language.Haskell.Syntax.Extension
-{-# LANGUAGE ViewPatterns         #-}
 
 {-# OPTIONS_GHC -Wno-orphans #-} -- Outputable
 
diff --git a/compiler/GHC/Hs/Type.hs b/compiler/GHC/Hs/Type.hs
index 4409756958..59fcaf9fe1 100644
--- a/compiler/GHC/Hs/Type.hs
+++ b/compiler/GHC/Hs/Type.hs
@@ -1,15 +1,13 @@
-{-# LANGUAGE CPP                   #-}
-{-# LANGUAGE ConstraintKinds       #-}
-{-# LANGUAGE DeriveDataTypeable    #-}
-{-# LANGUAGE FlexibleContexts      #-}
-{-# LANGUAGE FlexibleInstances     #-}
+{-# LANGUAGE CPP #-}
+{-# LANGUAGE ConstraintKinds #-}
+{-# LANGUAGE FlexibleContexts #-}
+{-# LANGUAGE FlexibleInstances #-}
 {-# LANGUAGE MultiParamTypeClasses #-}
-{-# LANGUAGE ScopedTypeVariables   #-}
-{-# LANGUAGE StandaloneDeriving    #-}
-{-# LANGUAGE TypeApplications      #-}
-{-# LANGUAGE TypeFamilies          #-}
-{-# LANGUAGE ViewPatterns          #-}
-{-# LANGUAGE UndecidableInstances  #-} -- Wrinkle in Note [Trees That Grow]
+{-# LANGUAGE ScopedTypeVariables #-}
+{-# LANGUAGE TypeApplications #-}
+{-# LANGUAGE TypeFamilies #-}
+{-# LANGUAGE ViewPatterns #-}
+{-# LANGUAGE UndecidableInstances #-} -- Wrinkle in Note [Trees That Grow]
                                        -- in module Language.Haskell.Syntax.Extension
 
 {-# OPTIONS_GHC -Wno-orphans #-} -- NamedThing, Outputable, OutputableBndrId
diff --git a/compiler/GHC/Parser/PostProcess.hs b/compiler/GHC/Parser/PostProcess.hs
index 9bf87b2e8b..9dde6faeb8 100644
--- a/compiler/GHC/Parser/PostProcess.hs
+++ b/compiler/GHC/Parser/PostProcess.hs
@@ -1,12 +1,12 @@
-{-# LANGUAGE CPP               #-}
-{-# LANGUAGE ConstraintKinds   #-}
-{-# LANGUAGE FlexibleContexts  #-}
+{-# LANGUAGE CPP #-}
+{-# LANGUAGE ConstraintKinds #-}
+{-# LANGUAGE FlexibleContexts #-}
 {-# LANGUAGE FlexibleInstances #-}
-{-# LANGUAGE GADTs             #-}
-{-# LANGUAGE RankNTypes        #-}
-{-# LANGUAGE TypeFamilies      #-}
-{-# LANGUAGE ViewPatterns      #-}
-{-# LANGUAGE LambdaCase        #-}
+{-# LANGUAGE GADTs #-}
+{-# LANGUAGE LambdaCase #-}
+{-# LANGUAGE RankNTypes #-}
+{-# LANGUAGE TypeFamilies #-}
+{-# LANGUAGE ViewPatterns #-}
 
 {-# OPTIONS_GHC -Wno-incomplete-record-updates #-}
 
diff --git a/compiler/GHC/Rename/Env.hs b/compiler/GHC/Rename/Env.hs
index 68c299a3b0..893e4ed60b 100644
--- a/compiler/GHC/Rename/Env.hs
+++ b/compiler/GHC/Rename/Env.hs
@@ -1,6 +1,4 @@
-{-# LANGUAGE CPP            #-}
-{-# LANGUAGE DeriveFunctor  #-}
-{-# LANGUAGE MultiWayIf #-}
+{-# LANGUAGE CPP #-}
 {-# LANGUAGE NamedFieldPuns #-}
 {-# LANGUAGE TypeApplications #-}
 
diff --git a/compiler/GHC/Runtime/Eval.hs b/compiler/GHC/Runtime/Eval.hs
index b90bb044c4..d8c8c781da 100644
--- a/compiler/GHC/Runtime/Eval.hs
+++ b/compiler/GHC/Runtime/Eval.hs
@@ -1,6 +1,5 @@
 {-# LANGUAGE BangPatterns #-}
 {-# LANGUAGE CPP #-}
-{-# LANGUAGE LambdaCase #-}
 {-# LANGUAGE RecordWildCards #-}
 
 {-# OPTIONS_GHC -Wno-incomplete-uni-patterns #-}
diff --git a/compiler/GHC/Runtime/Interpreter.hs b/compiler/GHC/Runtime/Interpreter.hs
index c4b266a534..d6f2979848 100644
--- a/compiler/GHC/Runtime/Interpreter.hs
+++ b/compiler/GHC/Runtime/Interpreter.hs
@@ -1,5 +1,7 @@
-{-# LANGUAGE RecordWildCards, ScopedTypeVariables, BangPatterns, CPP #-}
-{-# LANGUAGE LambdaCase #-}
+{-# LANGUAGE BangPatterns #-}
+{-# LANGUAGE CPP #-}
+{-# LANGUAGE RecordWildCards #-}
+{-# LANGUAGE ScopedTypeVariables #-}
 {-# LANGUAGE TupleSections #-}
 
 -- | Interacting with the iserv interpreter, whether it is running on an
diff --git a/compiler/GHC/StgToCmm/DataCon.hs b/compiler/GHC/StgToCmm/DataCon.hs
index 95e975fd0a..fbf7a01399 100644
--- a/compiler/GHC/StgToCmm/DataCon.hs
+++ b/compiler/GHC/StgToCmm/DataCon.hs
@@ -1,4 +1,3 @@
-{-# LANGUAGE TupleSections #-}
 {-# LANGUAGE CPP #-}
 
 -----------------------------------------------------------------------------
diff --git a/compiler/GHC/StgToCmm/Monad.hs b/compiler/GHC/StgToCmm/Monad.hs
index fec12e16c7..98720a2f50 100644
--- a/compiler/GHC/StgToCmm/Monad.hs
+++ b/compiler/GHC/StgToCmm/Monad.hs
@@ -1,10 +1,8 @@
-{-# LANGUAGE DeriveFunctor #-}
+{-# LANGUAGE FlexibleInstances #-}
 {-# LANGUAGE GADTs #-}
 {-# LANGUAGE MultiParamTypeClasses #-}
-{-# LANGUAGE FlexibleInstances #-}
 {-# LANGUAGE PatternSynonyms #-}
 
-
 -----------------------------------------------------------------------------
 --
 -- Monad for Stg to C-- code generation
diff --git a/compiler/GHC/Tc/Instance/Typeable.hs b/compiler/GHC/Tc/Instance/Typeable.hs
index 6c4aeaeb49..0de6ec4e78 100644
--- a/compiler/GHC/Tc/Instance/Typeable.hs
+++ b/compiler/GHC/Tc/Instance/Typeable.hs
@@ -4,10 +4,9 @@
 -}
 
 {-# LANGUAGE CPP #-}
-{-# LANGUAGE RecordWildCards #-}
 {-# LANGUAGE GeneralizedNewtypeDeriving #-}
+{-# LANGUAGE RecordWildCards #-}
 {-# LANGUAGE TypeFamilies #-}
-{-# LANGUAGE MultiWayIf #-}
 
 module GHC.Tc.Instance.Typeable(mkTypeableBinds, tyConIsTypeable) where
 
diff --git a/compiler/GHC/Tc/Solver/Monad.hs b/compiler/GHC/Tc/Solver/Monad.hs
index 063f409041..438339fcfd 100644
--- a/compiler/GHC/Tc/Solver/Monad.hs
+++ b/compiler/GHC/Tc/Solver/Monad.hs
@@ -1,5 +1,10 @@
-{-# LANGUAGE CPP, DeriveFunctor, TypeFamilies, ScopedTypeVariables, TypeApplications,
-             DerivingStrategies, GeneralizedNewtypeDeriving, ScopedTypeVariables #-}
+{-# LANGUAGE CPP #-}
+{-# LANGUAGE DeriveFunctor #-}
+{-# LANGUAGE DerivingStrategies #-}
+{-# LANGUAGE GeneralizedNewtypeDeriving #-}
+{-# LANGUAGE ScopedTypeVariables #-}
+{-# LANGUAGE TypeApplications #-}
+{-# LANGUAGE TypeFamilies #-}
 
 {-# OPTIONS_GHC -Wno-incomplete-record-updates -Wno-incomplete-uni-patterns #-}
 
diff --git a/compiler/GHC/ThToHs.hs b/compiler/GHC/ThToHs.hs
index 1009ea72f0..63055bbd48 100644
--- a/compiler/GHC/ThToHs.hs
+++ b/compiler/GHC/ThToHs.hs
@@ -1,12 +1,12 @@
-{-# LANGUAGE BangPatterns            #-}
-{-# LANGUAGE DeriveFunctor           #-}
-{-# LANGUAGE FlexibleContexts        #-}
-{-# LANGUAGE FunctionalDependencies  #-}
-{-# LANGUAGE LambdaCase              #-}
+{-# LANGUAGE BangPatterns #-}
 {-# LANGUAGE ConstrainedClassMethods #-}
-{-# LANGUAGE ScopedTypeVariables     #-}
-{-# LANGUAGE TypeFamilies            #-}
-{-# LANGUAGE ViewPatterns            #-}
+{-# LANGUAGE DeriveFunctor #-}
+{-# LANGUAGE FlexibleContexts #-}
+{-# LANGUAGE FunctionalDependencies #-}
+{-# LANGUAGE LambdaCase #-}
+{-# LANGUAGE ScopedTypeVariables #-}
+{-# LANGUAGE TypeFamilies #-}
+{-# LANGUAGE ViewPatterns #-}
 
 {-# OPTIONS_GHC -Wno-incomplete-record-updates #-}
 {-# OPTIONS_GHC -Wno-incomplete-uni-patterns   #-}
@@ -702,8 +702,7 @@ cvt_id_arg (i, str, ty)
                           , cd_fld_doc = Nothing}) }
 
 cvtDerivs :: [TH.DerivClause] -> CvtM (HsDeriving GhcPs)
-cvtDerivs cs = do { cs' <- mapM cvtDerivClause cs
-                  ; return cs' }
+cvtDerivs cs = do { mapM cvtDerivClause cs }
 
 cvt_fundep :: TH.FunDep -> CvtM (LHsFunDep GhcPs)
 cvt_fundep (TH.FunDep xs ys) = do { xs' <- mapM tNameN xs
diff --git a/compiler/GHC/Types/Unique/Supply.hs b/compiler/GHC/Types/Unique/Supply.hs
index 9f4d6744c9..0d27bb6ceb 100644
--- a/compiler/GHC/Types/Unique/Supply.hs
+++ b/compiler/GHC/Types/Unique/Supply.hs
@@ -3,11 +3,10 @@
 (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
 -}
 
+{-# LANGUAGE BangPatterns #-}
 {-# LANGUAGE CPP #-}
 {-# LANGUAGE MagicHash #-}
-{-# LANGUAGE DeriveFunctor #-}
 {-# LANGUAGE PatternSynonyms #-}
-{-# LANGUAGE BangPatterns #-}
 {-# LANGUAGE UnboxedTuples #-}
 
 module GHC.Types.Unique.Supply (