Suggestions due to hlint

It turns out this job hasn't been running for quite a while (perhaps
ever) so there are quite a few failures when running the linter locally.

27 files changed, 19 insertions, 49 deletions

diff --git a/compiler/.hlint.yaml b/compiler/.hlint.yaml
index a3b780ce62..ee4a04a37a 100644
--- a/compiler/.hlint.yaml
+++ b/compiler/.hlint.yaml
@@ -21,3 +21,6 @@
 # below.
 
 - ignore: {name: Redundant do, within: [GHC.SysTools.Terminal, GHC.Utils.Binary]}
+- ignore: {name: Use fewer imports, within: [GHC.Parser, GHC.Cmm.Parser ] }
+- ignore: {name: Redundant return, within: [GHC.Data.FastString] }
+- ignore: {within: [GHC.Parser, GHC.Parser.Lexer] }
diff --git a/compiler/GHC/Cmm/Config.hs b/compiler/GHC/Cmm/Config.hs
index 12eb4e47dc..415becd109 100644
--- a/compiler/GHC/Cmm/Config.hs
+++ b/compiler/GHC/Cmm/Config.hs
@@ -1,7 +1,6 @@
 -- | Cmm compilation configuration
 
 {-# LANGUAGE DerivingStrategies         #-}
-{-# LANGUAGE GeneralizedNewtypeDeriving #-}
 
 module GHC.Cmm.Config
   ( CmmConfig(..)
diff --git a/compiler/GHC/Cmm/Parser.y b/compiler/GHC/Cmm/Parser.y
index 5a855ba069..6e6a130233 100644
--- a/compiler/GHC/Cmm/Parser.y
+++ b/compiler/GHC/Cmm/Parser.y
@@ -214,7 +214,6 @@ import GHC.Platform
 import GHC.Platform.Profile
 
 import GHC.StgToCmm.ExtCode
-import GHC.StgToCmm.Prof
 import GHC.StgToCmm.Heap
 import GHC.StgToCmm.Monad hiding ( getCode, getCodeR, getCodeScoped, emitLabel, emit
                                  , emitStore, emitAssign, emitOutOfLine, withUpdFrameOff
diff --git a/compiler/GHC/Core/LateCC.hs b/compiler/GHC/Core/LateCC.hs
index d7a3b0cd8d..634eabc4f6 100644
--- a/compiler/GHC/Core/LateCC.hs
+++ b/compiler/GHC/Core/LateCC.hs
@@ -1,8 +1,3 @@
-{-# LANGUAGE NamedFieldPuns #-}
-{-# LANGUAGE TypeApplications #-}
-{-# LANGUAGE DeriveGeneric #-}
-{-# LANGUAGE DeriveDataTypeable #-}
-{-# LANGUAGE DeriveAnyClass #-}
 {-# LANGUAGE DerivingStrategies #-}
 {-# LANGUAGE TupleSections #-}
 
diff --git a/compiler/GHC/Core/Opt/DmdAnal.hs b/compiler/GHC/Core/Opt/DmdAnal.hs
index cd58ff89d7..2dafaf8e0b 100644
--- a/compiler/GHC/Core/Opt/DmdAnal.hs
+++ b/compiler/GHC/Core/Opt/DmdAnal.hs
@@ -1946,8 +1946,7 @@ If we make the dictionary strict then WW can fire turning this into:
 Which *usually* performs better. However if the dictionary is known we
 are far more likely to inline a function applied to the dictionary than
 to inline one applied to a function. Sometimes this makes just enough
-of a difference to stop a function from inlining. This is documented in
-#18421.
+of a difference to stop a function from inlining. This is documented in #18421.
 
 It's somewhat similar to Note [Do not unbox class dictionaries] although
 here our problem is with the inliner, not the specializer.
diff --git a/compiler/GHC/Core/Opt/WorkWrap/Utils.hs b/compiler/GHC/Core/Opt/WorkWrap/Utils.hs
index 8936ccdfe5..5f450b9316 100644
--- a/compiler/GHC/Core/Opt/WorkWrap/Utils.hs
+++ b/compiler/GHC/Core/Opt/WorkWrap/Utils.hs
@@ -6,7 +6,6 @@ A library for the ``worker\/wrapper'' back-end to the strictness analyser
 
 
 {-# LANGUAGE ViewPatterns #-}
-{-# LANGUAGE GeneralizedNewtypeDeriving #-}
 
 module GHC.Core.Opt.WorkWrap.Utils
    ( WwOpts(..), initWwOpts, mkWwBodies, mkWWstr, mkWWstr_one, mkWorkerArgs
diff --git a/compiler/GHC/Core/Subst.hs b/compiler/GHC/Core/Subst.hs
index 5a6beca0f7..172e8ac67d 100644
--- a/compiler/GHC/Core/Subst.hs
+++ b/compiler/GHC/Core/Subst.hs
@@ -748,8 +748,7 @@ This time the call stack looked something like:
 and the rule was
 
 {-# RULES
-"transpose/overlays1" forall xs. transpose (overlays1 xs) = overlays1 (fmap transpose xs)
-#-}
+"transpose/overlays1" forall xs. transpose (overlays1 xs) = overlays1 (fmap transpose xs) #-}
 
 This rule was attached to `transpose`, but also mentions itself in the RHS so we have
 to be careful to not force the `IdInfo` for transpose when dealing with the RHS of the rule.
diff --git a/compiler/GHC/Core/Type.hs b/compiler/GHC/Core/Type.hs
index 4fce8c8a09..2406fc6e7a 100644
--- a/compiler/GHC/Core/Type.hs
+++ b/compiler/GHC/Core/Type.hs
@@ -3,7 +3,7 @@
 --
 -- Type - public interface
 
-{-# LANGUAGE FlexibleContexts, PatternSynonyms, ViewPatterns, MultiWayIf #-}
+{-# LANGUAGE FlexibleContexts, PatternSynonyms, ViewPatterns #-}
 {-# OPTIONS_GHC -fno-warn-orphans #-}
 {-# OPTIONS_GHC -Wno-incomplete-record-updates #-}
 
diff --git a/compiler/GHC/Core/Unify.hs b/compiler/GHC/Core/Unify.hs
index a18899ec09..52e2a97ca2 100644
--- a/compiler/GHC/Core/Unify.hs
+++ b/compiler/GHC/Core/Unify.hs
@@ -2,7 +2,7 @@
 
 {-# LANGUAGE ScopedTypeVariables, PatternSynonyms #-}
 
-{-# LANGUAGE DeriveFunctor, DeriveDataTypeable #-}
+{-# LANGUAGE DeriveFunctor #-}
 
 module GHC.Core.Unify (
         tcMatchTy, tcMatchTyKi,
diff --git a/compiler/GHC/Data/FastString.hs b/compiler/GHC/Data/FastString.hs
index 1d9e419418..131f174c41 100644
--- a/compiler/GHC/Data/FastString.hs
+++ b/compiler/GHC/Data/FastString.hs
@@ -537,8 +537,7 @@ mkFastString str =
 -- The following rule is used to avoid polluting the non-reclaimable FastString
 -- table with transient strings when we only want their encoding.
 {-# RULES
-"bytesFS/mkFastString" forall x. bytesFS (mkFastString x) = utf8EncodeString x
-#-}
+"bytesFS/mkFastString" forall x. bytesFS (mkFastString x) = utf8EncodeString x #-}
 
 -- | Creates a 'FastString' from a UTF-8 encoded @[Word8]@
 mkFastStringByteList :: [Word8] -> FastString
diff --git a/compiler/GHC/Driver/Make.hs b/compiler/GHC/Driver/Make.hs
index 2c0e074216..3059154ff5 100644
--- a/compiler/GHC/Driver/Make.hs
+++ b/compiler/GHC/Driver/Make.hs
@@ -2,8 +2,6 @@
 {-# LANGUAGE DeriveTraversable #-}
 {-# LANGUAGE NamedFieldPuns #-}
 {-# LANGUAGE NondecreasingIndentation #-}
-{-# LANGUAGE LambdaCase #-}
-{-# LANGUAGE RecordWildCards #-}
 {-# LANGUAGE ScopedTypeVariables #-}
 
 {-# OPTIONS_GHC -Wno-incomplete-uni-patterns #-}
@@ -16,9 +14,9 @@
 {-# LANGUAGE GeneralisedNewtypeDeriving #-}
 {-# LANGUAGE TupleSections #-}
 {-# LANGUAGE ApplicativeDo #-}
-{-# LANGUAGE TupleSections #-}
 {-# LANGUAGE MultiWayIf #-}
 {-# LANGUAGE CPP #-}
+{-# LANGUAGE RecordWildCards #-}
 
 -- -----------------------------------------------------------------------------
 --
@@ -2437,7 +2435,7 @@ R.hs:        module R where
                 g = ...f...
 ```
 
-## Why we need to rehydrate A's ModIface before compiling R.hs
+== Why we need to rehydrate A's ModIface before compiling R.hs
 
 After compiling A.hs we'll have a TypeEnv in which the Id for `f` has a type
 type uses the AbstractTyCon T; and a TyCon for `S` that also mentions that same
@@ -2457,7 +2455,7 @@ Now `S` will be bound to a thunk that, when forced, will "see" the final binding
 for `T`; see [Tying the knot](https://gitlab.haskell.org/ghc/ghc/-/wikis/commentary/compiler/tying-the-knot).
 But note that this must be done *before* compiling R.hs.
 
-## Why we need to rehydrate A's ModIface after compiling R.hs
+== Why we need to rehydrate A's ModIface after compiling R.hs
 
 When compiling R.hs, the knot-tying stuff above will ensure that `f`'s unfolding
 mentions the `LocalId` for `g`.  But when we finish R, we carefully ensure that
@@ -2468,7 +2466,7 @@ subsequent modules that import A will see a crippled unfolding for `f`.
 
 Solution: rehydrate both R and A's ModIface together, right after completing R.hs.
 
-## Which modules to rehydrate
+~~ Which modules to rehydrate
 
 We only need rehydrate modules that are
 * Below R.hs
@@ -2477,7 +2475,7 @@ We only need rehydrate modules that are
 There might be many unrelated modules (in the home package) that don't need to be
 rehydrated.
 
-## Modules "above" the loop
+== Modules "above" the loop
 
 This dark corner is the subject of #14092.
 
diff --git a/compiler/GHC/Parser.y b/compiler/GHC/Parser.y
index 4be8d39c5d..3918c752b9 100644
--- a/compiler/GHC/Parser.y
+++ b/compiler/GHC/Parser.y
@@ -6,11 +6,8 @@
 --
 -- Author(s): Simon Marlow, Sven Panne 1997, 1998, 1999
 -- ---------------------------------------------------------------------------
-
 {
-{-# LANGUAGE ViewPatterns #-}
 {-# LANGUAGE TypeFamilies #-}
-{-# LANGUAGE LambdaCase #-}
 {-# LANGUAGE RankNTypes #-}
 {-# LANGUAGE DataKinds #-}
 {-# LANGUAGE GADTs #-}
@@ -48,8 +45,6 @@ import Data.List.NonEmpty ( NonEmpty(..) )
 import qualified Data.List.NonEmpty as NE
 import qualified Prelude -- for happy-generated code
 
-import GHC.Prelude
-
 import GHC.Hs
 
 import GHC.Driver.Backpack.Syntax
diff --git a/compiler/GHC/Parser/Lexer.x b/compiler/GHC/Parser/Lexer.x
index 7bcff45ed8..7d7d157d2b 100644
--- a/compiler/GHC/Parser/Lexer.x
+++ b/compiler/GHC/Parser/Lexer.x
@@ -42,7 +42,6 @@
 
 {
 {-# LANGUAGE BangPatterns #-}
-{-# LANGUAGE DeriveDataTypeable #-}
 {-# LANGUAGE LambdaCase #-}
 {-# LANGUAGE MultiWayIf #-}
 {-# LANGUAGE UnboxedTuples #-}
@@ -50,6 +49,7 @@
 {-# LANGUAGE UnliftedNewtypes #-}
 {-# LANGUAGE PatternSynonyms #-}
 
+
 {-# OPTIONS_GHC -funbox-strict-fields #-}
 {-# OPTIONS_GHC -Wno-incomplete-uni-patterns #-}
 
diff --git a/compiler/GHC/Parser/PostProcess/Haddock.hs b/compiler/GHC/Parser/PostProcess/Haddock.hs
index 4d85c65ef5..08bebc4683 100644
--- a/compiler/GHC/Parser/PostProcess/Haddock.hs
+++ b/compiler/GHC/Parser/PostProcess/Haddock.hs
@@ -2,7 +2,6 @@
 {-# LANGUAGE DeriveFunctor              #-}
 {-# LANGUAGE DerivingVia                #-}
 {-# LANGUAGE FlexibleInstances          #-}
-{-# LANGUAGE GeneralizedNewtypeDeriving #-}
 {-# LANGUAGE NamedFieldPuns             #-}
 {-# LANGUAGE RankNTypes                 #-}
 {-# LANGUAGE ScopedTypeVariables        #-}
diff --git a/compiler/GHC/Stg/InferTags/Rewrite.hs b/compiler/GHC/Stg/InferTags/Rewrite.hs
index 8b2c24cbdb..099fbc54d5 100644
--- a/compiler/GHC/Stg/InferTags/Rewrite.hs
+++ b/compiler/GHC/Stg/InferTags/Rewrite.hs
@@ -420,7 +420,6 @@ rewriteApp True (StgApp f []) = do
                 then setIdTagSig f (TagSig TagProper)
                 else f
     return $! StgApp f' []
-  where
 rewriteApp _ (StgApp f args)
     -- | pprTrace "rewriteAppOther" (ppr f <+> ppr args) False
     -- = undefined
diff --git a/compiler/GHC/Stg/Lift/Config.hs b/compiler/GHC/Stg/Lift/Config.hs
index 1413bd5edc..544c23f6a4 100644
--- a/compiler/GHC/Stg/Lift/Config.hs
+++ b/compiler/GHC/Stg/Lift/Config.hs
@@ -1,4 +1,3 @@
-{-# LANGUAGE GeneralizedNewtypeDeriving #-}
 {-# LANGUAGE TypeFamilies #-}
 
 -- | Configuration options for Lift the lambda lifter.
diff --git a/compiler/GHC/Stg/Utils.hs b/compiler/GHC/Stg/Utils.hs
index 4561e25765..62aa89f0ff 100644
--- a/compiler/GHC/Stg/Utils.hs
+++ b/compiler/GHC/Stg/Utils.hs
@@ -1,5 +1,4 @@
 {-# LANGUAGE CPP, ScopedTypeVariables, TypeFamilies #-}
-{-# LANGUAGE BangPatterns #-}
 {-# LANGUAGE DataKinds #-}
 
 module GHC.Stg.Utils
diff --git a/compiler/GHC/Tc/Deriv/Generate.hs b/compiler/GHC/Tc/Deriv/Generate.hs
index 7d5ae9d763..7c03f52bd0 100644
--- a/compiler/GHC/Tc/Deriv/Generate.hs
+++ b/compiler/GHC/Tc/Deriv/Generate.hs
@@ -70,11 +70,10 @@ import GHC.Builtin.Types.Prim
 import GHC.Builtin.Types
 import GHC.Core.Type
 import GHC.Core.Class
-import GHC.Types.Unique.FM ( lookupUFM )
+import GHC.Types.Unique.FM ( lookupUFM, listToUFM )
 import GHC.Types.Var.Set
 import GHC.Types.Var.Env
 import GHC.Utils.Misc
-import GHC.Types.Unique.FM ( listToUFM )
 import GHC.Types.Var
 import GHC.Utils.Outputable
 import GHC.Utils.Panic
diff --git a/compiler/GHC/Tc/Errors.hs b/compiler/GHC/Tc/Errors.hs
index b71a6b1dd4..596271b065 100644
--- a/compiler/GHC/Tc/Errors.hs
+++ b/compiler/GHC/Tc/Errors.hs
@@ -1,13 +1,11 @@
 
 {-# LANGUAGE LambdaCase          #-}
 {-# LANGUAGE NamedFieldPuns      #-}
-{-# LANGUAGE RecordWildCards     #-}
 {-# LANGUAGE ScopedTypeVariables #-}
 {-# LANGUAGE TupleSections       #-}
 
 {-# OPTIONS_GHC -Wno-incomplete-uni-patterns   #-}
 {-# OPTIONS_GHC -Wno-incomplete-record-updates #-}
-{-# LANGUAGE TupleSections #-}
 {-# LANGUAGE ParallelListComp #-}
 
 module GHC.Tc.Errors(
@@ -86,10 +84,9 @@ import Control.Monad    ( unless, when, foldM, forM_ )
 import Data.Foldable    ( toList )
 import Data.Functor     ( (<&>) )
 import Data.Function    ( on )
-import Data.List        ( partition, sort )
+import Data.List        ( partition, sort, sortBy )
 import Data.List.NonEmpty ( NonEmpty(..), (<|) )
 import qualified Data.List.NonEmpty as NE ( map, reverse )
-import Data.List        ( sortBy )
 import Data.Ord         ( comparing )
 import qualified Data.Semigroup as S
 
diff --git a/compiler/GHC/Tc/Utils/TcMType.hs b/compiler/GHC/Tc/Utils/TcMType.hs
index 3c978b511c..cbbdcdfb47 100644
--- a/compiler/GHC/Tc/Utils/TcMType.hs
+++ b/compiler/GHC/Tc/Utils/TcMType.hs
@@ -3,7 +3,6 @@
 {-# LANGUAGE TupleSections   #-}
 
 {-# OPTIONS_GHC -Wno-incomplete-record-updates #-}
-{-# LANGUAGE LambdaCase #-}
 {-
 (c) The University of Glasgow 2006
 (c) The GRASP/AQUA Project, Glasgow University, 1992-1998
diff --git a/compiler/GHC/Types/Demand.hs b/compiler/GHC/Types/Demand.hs
index 7376a610d4..0cfb0dae29 100644
--- a/compiler/GHC/Types/Demand.hs
+++ b/compiler/GHC/Types/Demand.hs
@@ -215,8 +215,7 @@ Here are reasons for too much optimism:
  * Note [lubBoxity and plusBoxity] describes why we optimistically let Unboxed
    win when combining different case alternatives.
 
-Boxity analysis fixes a number of issues:
-#19871, #19407, #4267, #16859, #18907, #13331
+Boxity analysis fixes a number of issues: #19871, #19407, #4267, #16859, #18907, #13331
 
 Note [Function body boxity and call sites]
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
diff --git a/compiler/GHC/Unit/Finder.hs b/compiler/GHC/Unit/Finder.hs
index c7b6a2eb65..c3c517cb18 100644
--- a/compiler/GHC/Unit/Finder.hs
+++ b/compiler/GHC/Unit/Finder.hs
@@ -5,7 +5,6 @@
 
 
 {-# LANGUAGE FlexibleContexts #-}
-{-# LANGUAGE MultiWayIf #-}
 
 -- | Module finder
 module GHC.Unit.Finder (
diff --git a/compiler/GHC/Unit/Module/Deps.hs b/compiler/GHC/Unit/Module/Deps.hs
index 0da8a06979..c654940730 100644
--- a/compiler/GHC/Unit/Module/Deps.hs
+++ b/compiler/GHC/Unit/Module/Deps.hs
@@ -400,13 +400,13 @@ it would recompile nearly every module in your project, just to update this info
 Now, we are a bit more careful about what we store and
 explicitly store transitive information only if it is really needed.
 
-# Direct Information
+~ Direct Information
 
 * dep_direct_mods - Directly imported home package modules
 * dep_direct_pkgs - Directly imported packages
 * dep_plgins      - Directly used plugins
 
-# Transitive Information
+~ Transitive Information
 
 Some features of the compiler require transitive information about what is currently
 being compiled, so that is explicitly stored separately in the form they need.
diff --git a/compiler/GHC/Unit/Module/Env.hs b/compiler/GHC/Unit/Module/Env.hs
index 0c8016e17e..e8307229f7 100644
--- a/compiler/GHC/Unit/Module/Env.hs
+++ b/compiler/GHC/Unit/Module/Env.hs
@@ -1,4 +1,3 @@
-{-# LANGUAGE GeneralizedNewtypeDeriving #-}
 -- | Module environment
 module GHC.Unit.Module.Env
    ( -- * Module mappings
diff --git a/compiler/GHC/Unit/Module/Graph.hs b/compiler/GHC/Unit/Module/Graph.hs
index 2a791b42b5..f71c71347f 100644
--- a/compiler/GHC/Unit/Module/Graph.hs
+++ b/compiler/GHC/Unit/Module/Graph.hs
@@ -1,6 +1,5 @@
 {-# LANGUAGE LambdaCase      #-}
 {-# LANGUAGE RecordWildCards #-}
-{-# LANGUAGE DeriveFunctor #-}
 {-# LANGUAGE DeriveTraversable #-}
 
 module GHC.Unit.Module.Graph
diff --git a/compiler/GHC/Unit/Module/ModSummary.hs b/compiler/GHC/Unit/Module/ModSummary.hs
index 3fd972632f..6c0ff55627 100644
--- a/compiler/GHC/Unit/Module/ModSummary.hs
+++ b/compiler/GHC/Unit/Module/ModSummary.hs
@@ -1,4 +1,3 @@
-{-# LANGUAGE LambdaCase #-}
 {-# LANGUAGE TupleSections #-}
 
 -- | A ModSummary is a node in the compilation manager's dependency graph
diff --git a/compiler/GHC/Utils/Monad/State/Strict.hs b/compiler/GHC/Utils/Monad/State/Strict.hs
index b7cafb7f52..9778d1af80 100644
--- a/compiler/GHC/Utils/Monad/State/Strict.hs
+++ b/compiler/GHC/Utils/Monad/State/Strict.hs
@@ -1,4 +1,3 @@
-{-# LANGUAGE DeriveFunctor #-}
 {-# LANGUAGE UnboxedTuples #-}
 {-# LANGUAGE PatternSynonyms #-}