New -Wx-partial warnings with ghc 9.8

[geekosaur]

Problem Description

ghc 9.8 produces a great many warnings about partial functions, mostly head and tail.

Steps to Reproduce

Build xmonad-contrib with ghc 9.8 alpha3. (I will repeat this with alpha4 when it is available.)
This currently requires a patched setlocale package and an allow-newer on hsc2hs, which I am taking up with the respective upstreams.

A possibly useful cabal.project is:

packages: */*.cabal
-- setlocale and xmonad-contrib packages
with-compiler: ghc-9.8
allow-newer: hsc2hs:base

Configuration File

Please include the smallest full configuration file that reproduces
the problem you are experiencing:

module Main (main) where

import XMonad

main :: IO ()
main = xmonad def

Checklist

• I've read CONTRIBUTING.md

• I tested my configuration

  • With xmonad version 0.17.2
  • With xmonad-contrib version 0.17.1.9 (commit 51ba23b if using git)

[geekosaur]

XMonad/Layout/Grid.hs:64:69: warning: [GHC-63394] [-Wx-partial]
    In the use of ‘tail’
    (imported from Prelude, but defined in GHC.List):
    "This is a partial function, it throws an error on empty lists. Replace it with drop 1, or use pattern matching or Data.List.uncons instead. Consider refactoring to use Data.List.NonEmpty."
   |
64 |     chop n m = ((0, m - k * fromIntegral (pred n)) :) . map (, k) . tail . reverse . take n . tail . iterate (subtract k') $ m'
   |                                                                     ^^^^

XMonad/Layout/Grid.hs:64:95: warning: [GHC-63394] [-Wx-partial]
    In the use of ‘tail’
    (imported from Prelude, but defined in GHC.List):
    "This is a partial function, it throws an error on empty lists. Replace it with drop 1, or use pattern matching or Data.List.uncons instead. Consider refactoring to use Data.List.NonEmpty."
   |
64 |     chop n m = ((0, m - k * fromIntegral (pred n)) :) . map (, k) . tail . reverse . take n . tail . iterate (subtract k') $ m'
   |                                                                                               ^^^^

XMonad/Layout/OneBig.hs:68:22: warning: [GHC-63394] [-Wx-partial]
    In the use of ‘head’
    (imported from Prelude, but defined in GHC.List):
    "This is a partial function, it throws an error on empty lists. Use pattern matching or Data.List.uncons instead. Consider refactoring to use Data.List.NonEmpty."
   |
68 |             master = head ws
   |                      ^^^^

XMonad/Layout/OneBig.hs:69:22: warning: [GHC-63394] [-Wx-partial]
    In the use of ‘tail’
    (imported from Prelude, but defined in GHC.List):
    "This is a partial function, it throws an error on empty lists. Replace it with drop 1, or use pattern matching or Data.List.uncons instead. Consider refactoring to use Data.List.NonEmpty."
   |
69 |             other  = tail ws
   |                      ^^^^

XMonad/Layout/Spiral.hs:48:34: warning: [GHC-63394] [-Wx-partial]
    In the use of ‘tail’
    (imported from Prelude, but defined in GHC.List):
    "This is a partial function, it throws an error on empty lists. Replace it with drop 1, or use pattern matching or Data.List.uncons instead. Consider refactoring to use Data.List.NonEmpty."
   |
48 | fibs = 1 : 1 : zipWith (+) fibs (tail fibs)
   |                                  ^^^^

XMonad/Layout/Spiral.hs:85:82: warning: [GHC-63394] [-Wx-partial]
    In the use of ‘tail’
    (imported from Prelude, but defined in GHC.List):
    "This is a partial function, it throws an error on empty lists. Replace it with drop 1, or use pattern matching or Data.List.uncons instead. Consider refactoring to use Data.List.NonEmpty."
   |
85 |               ratios = blend scale . reverse . take (length ws - 1) . mkRatios $ tail fibs
   |                                                                                  ^^^^

XMonad/Layout/MultiColumns.hs:99:90: warning: [GHC-63394] [-Wx-partial]
    In the use of ‘tail’
    (imported from XMonad.Prelude, but defined in GHC.List):
    "This is a partial function, it throws an error on empty lists. Replace it with drop 1, or use pattern matching or Data.List.uncons instead. Consider refactoring to use Data.List.NonEmpty."
   |
99 |                   incmastern (IncMasterN x) = l { multiColNWin = take a n ++ [newval] ++ tail r }
   |                                                                                          ^^^^

XMonad/Layout/MultiColumns.hs:100:47: warning: [GHC-63394] [-Wx-partial]
    In the use of ‘head’
    (imported from XMonad.Prelude, but defined in GHC.List):
    "This is a partial function, it throws an error on empty lists. Use pattern matching or Data.List.uncons instead. Consider refactoring to use Data.List.NonEmpty."
    |
100 |                       where newval =  max 0 $ head r + x
    |                                               ^^^^

XMonad/Layout/CenteredMaster.hs:86:21: warning: [GHC-63394] [-Wx-partial]
    In the use of ‘head’
    (imported from Prelude, but defined in GHC.List):
    "This is a partial function, it throws an error on empty lists. Use pattern matching or Data.List.uncons instead. Consider refactoring to use Data.List.NonEmpty."
   |
86 |        let firstW = head ws
   |                     ^^^^

XMonad/Layout/CenteredMaster.hs:87:21: warning: [GHC-63394] [-Wx-partial]
    In the use of ‘tail’
    (imported from Prelude, but defined in GHC.List):
    "This is a partial function, it throws an error on empty lists. Replace it with drop 1, or use pattern matching or Data.List.uncons instead. Consider refactoring to use Data.List.NonEmpty."
   |
87 |        let other  = tail ws
   |                     ^^^^

XMonad/Hooks/InsertPosition.hs:86:27: warning: [GHC-63394] [-Wx-partial]
    In the use of ‘tail’
    (imported from Prelude, but defined in GHC.List):
    "This is a partial function, it throws an error on empty lists. Replace it with drop 1, or use pattern matching or Data.List.uncons instead. Consider refactoring to use Data.List.NonEmpty."
   |
86 |     in W.Stack (last ws) (tail $ reverse ws) []
   |                           ^^^^

XMonad/Actions/RotSlaves.hs:47:54: warning: [GHC-63394] [-Wx-partial]
    In the use of ‘tail’
    (imported from XMonad.Prelude, but defined in GHC.List):
    "This is a partial function, it throws an error on empty lists. Replace it with drop 1, or use pattern matching or Data.List.uncons instead. Consider refactoring to use Data.List.NonEmpty."
   |
47 | rotSlavesUp   = windows $ modify' (rotSlaves' (\l -> tail l++[head l]))
   |                                                      ^^^^

XMonad/Actions/RotSlaves.hs:47:63: warning: [GHC-63394] [-Wx-partial]
    In the use of ‘head’
    (imported from XMonad.Prelude, but defined in GHC.List):
    "This is a partial function, it throws an error on empty lists. Use pattern matching or Data.List.uncons instead. Consider refactoring to use Data.List.NonEmpty."
   |
47 | rotSlavesUp   = windows $ modify' (rotSlaves' (\l -> tail l++[head l]))
   |                                                               ^^^^

XMonad/Actions/RotSlaves.hs:60:48: warning: [GHC-63394] [-Wx-partial]
    In the use of ‘tail’
    (imported from XMonad.Prelude, but defined in GHC.List):
    "This is a partial function, it throws an error on empty lists. Replace it with drop 1, or use pattern matching or Data.List.uncons instead. Consider refactoring to use Data.List.NonEmpty."
   |
60 | rotAllUp   = windows $ modify' (rotAll' (\l -> tail l++[head l]))
   |                                                ^^^^

XMonad/Actions/RotSlaves.hs:60:57: warning: [GHC-63394] [-Wx-partial]
    In the use of ‘head’
    (imported from XMonad.Prelude, but defined in GHC.List):
    "This is a partial function, it throws an error on empty lists. Use pattern matching or Data.List.uncons instead. Consider refactoring to use Data.List.NonEmpty."
   |
60 | rotAllUp   = windows $ modify' (rotAll' (\l -> tail l++[head l]))
   |                                                         ^^^^

XMonad/Actions/OnScreen.hs:145:23: warning: [GHC-63394] [-Wx-partial]
    In the use of ‘head’
    (imported from Prelude, but defined in GHC.List):
    "This is a partial function, it throws an error on empty lists. Use pattern matching or Data.List.uncons instead. Consider refactoring to use Data.List.NonEmpty."
    |
145 |     return $ f (tag . head $ st') st
    |                       ^^^^

XMonad/Actions/MessageFeedback.hs:50:39: warning: [GHC-38856] [-Wunused-imports]
    The import of ‘liftA2’ from module ‘XMonad.Prelude’ is redundant
   |
50 | import XMonad.Prelude       ( isJust, liftA2, void )
   |                                       ^^^^^^

XMonad/Actions/CycleSelectedLayouts.hs:45:28: warning: [GHC-63394] [-Wx-partial]
    In the use of ‘head’
    (imported from Prelude, but defined in GHC.List):
    "This is a partial function, it throws an error on empty lists. Use pattern matching or Data.List.uncons instead. Consider refactoring to use Data.List.NonEmpty."
   |
45 |     let newld = fromMaybe (head lst) (cycleToNext lst ld)
   |                            ^^^^

XMonad/Util/DebugWindow.hs:62:64: warning: [GHC-63394] [-Wx-partial]
    In the use of ‘tail’
    (imported from XMonad.Prelude, but defined in GHC.List):
    "This is a partial function, it throws an error on empty lists. Replace it with drop 1, or use pattern matching or Data.List.uncons instead. Consider refactoring to use Data.List.NonEmpty."
   |
62 |                                                           else tail s''
   |                                                                ^^^^

XMonad/Hooks/DebugEvents.hs:36:1: warning: [GHC-66111] [-Wunused-imports]
    The import of ‘Control.Monad.Fail’ is redundant
      except perhaps to import instances from ‘Control.Monad.Fail’
    To import instances alone, use: import Control.Monad.Fail()
   |
36 | import           Control.Monad.Fail
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

XMonad/Hooks/DebugEvents.hs:692:75: warning: [GHC-63394] [-Wx-partial]
    In the use of ‘tail’
    (imported from XMonad.Prelude, but defined in GHC.List):
    "This is a partial function, it throws an error on empty lists. Replace it with drop 1, or use pattern matching or Data.List.uncons instead. Consider refactoring to use Data.List.NonEmpty."
    |
692 |                                                                      else tail s''
    |                                                                           ^^^^

XMonad/Util/Image.hs:45:26: warning: [GHC-63394] [-Wx-partial]
    In the use of ‘head’
    (imported from Prelude, but defined in GHC.List):
    "This is a partial function, it throws an error on empty lists. Use pattern matching or Data.List.uncons instead. Consider refactoring to use Data.List.NonEmpty."
   |
45 | imageDims img = (length (head img), length img)
   |                          ^^^^

XMonad/Hooks/WorkspaceHistory.hs:93:23: warning: [GHC-63394] [-Wx-partial]
    In the use of ‘head’
    (imported from Prelude, but defined in GHC.List):
    "This is a partial function, it throws an error on empty lists. Use pattern matching or Data.List.uncons instead. Consider refactoring to use Data.List.NonEmpty."
   |
93 |   map (\wss -> (fst $ head wss, map snd wss)) .
   |                       ^^^^

XMonad/Hooks/WallpaperSetter.hs:143:42: warning: [GHC-63394] [-Wx-partial]
    In the use of ‘head’
    (imported from XMonad.Prelude, but defined in GHC.List):
    "This is a partial function, it throws an error on empty lists. Use pattern matching or Data.List.uncons instead. Consider refactoring to use Data.List.NonEmpty."
    |
143 |             let files' = filter ((/='.').head) files
    |                                          ^^^^

XMonad/Hooks/CurrentWorkspaceOnTop.hs:67:33: warning: [GHC-63394] [-Wx-partial]
    In the use of ‘head’
    (imported from Prelude, but defined in GHC.List):
    "This is a partial function, it throws an error on empty lists. Use pattern matching or Data.List.uncons instead. Consider refactoring to use Data.List.NonEmpty."
   |
67 |             io $ raiseWindow d (head wins)  -- raise first window of current workspace to the very top,
   |                                 ^^^^

XMonad/Actions/Workscreen.hs:112:40: warning: [GHC-63394] [-Wx-partial]
    In the use of ‘head’
    (imported from XMonad.Prelude, but defined in GHC.List):
    "This is a partial function, it throws an error on empty lists. Use pattern matching or Data.List.uncons instead. Consider refactoring to use Data.List.NonEmpty."
    |
112 |                               let ws = head . workspaces $ a !! wscrId
    |                                        ^^^^

XMonad/Actions/SwapPromote.hs:243:30: warning: [GHC-63394] [-Wx-partial]
    In the use of ‘head’
    (imported from XMonad.Prelude, but defined in GHC.List):
    "This is a partial function, it throws an error on empty lists. Use pattern matching or Data.List.uncons instead. Consider refactoring to use Data.List.NonEmpty."
    |
243 |                 mh = let w = head . W.integrate $ s3
    |                              ^^^^

XMonad/Actions/MostRecentlyUsed.hs:40:1: warning: [GHC-66111] [-Wunused-imports]
    The import of ‘Control.Applicative’ is redundant
      except perhaps to import instances from ‘Control.Applicative’
    To import instances alone, use: import Control.Applicative()
   |
40 | import Control.Applicative (liftA2)
   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

XMonad/Hooks/ServerMode.hs:95:35: warning: [GHC-63394] [-Wx-partial]
    In the use of ‘head’
    (imported from XMonad.Prelude, but defined in GHC.List):
    "This is a partial function, it throws an error on empty lists. Use pattern matching or Data.List.uncons instead. Consider refactoring to use Data.List.NonEmpty."
   |
95 |          let atom = fromIntegral (head dt)
   |                                   ^^^^

XMonad/Util/Stack.hs:165:66: warning: [GHC-63394] [-Wx-partial]
    In the use of ‘tail’
    (imported from Prelude, but defined in GHC.List):
    "This is a partial function, it throws an error on empty lists. Replace it with drop 1, or use pattern matching or Data.List.uncons instead. Consider refactoring to use Data.List.NonEmpty."
    |
165 | focusUpZ (Just (W.Stack f _ down)) = Just $ W.Stack (last down) (tail (reverse down) ++ [f]) []
    |                                                                  ^^^^

XMonad/Util/Stack.hs:172:67: warning: [GHC-63394] [-Wx-partial]
    In the use of ‘tail’
    (imported from Prelude, but defined in GHC.List):
    "This is a partial function, it throws an error on empty lists. Replace it with drop 1, or use pattern matching or Data.List.uncons instead. Consider refactoring to use Data.List.NonEmpty."
    |
172 | focusDownZ (Just (W.Stack f up _)) = Just $ W.Stack (last up) [] (tail (reverse up) ++ [f])
    |                                                                   ^^^^

XMonad/Util/Stack.hs:178:36: warning: [GHC-63394] [-Wx-partial]
    In the use of ‘tail’
    (imported from Prelude, but defined in GHC.List):
    "This is a partial function, it throws an error on empty lists. Replace it with drop 1, or use pattern matching or Data.List.uncons instead. Consider refactoring to use Data.List.NonEmpty."
    |
178 |     = Just $ W.Stack (last up) [] (tail (reverse up) ++ [f] ++ down)
    |                                    ^^^^

XMonad/Layout/Groups.hs:201:71: warning: [GHC-63394] [-Wx-partial]
    In the use of ‘head’
    (imported from XMonad.Prelude, but defined in GHC.List):
    "This is a partial function, it throws an error on empty lists. Use pattern matching or Data.List.uncons instead. Consider refactoring to use Data.List.NonEmpty."
    |
201 |                        defaultGroups = fromJust $ singletonZ $ G (ID (head ids) $ baseLayout g) emptyZ
    |                                                                       ^^^^

XMonad/Layout/Groups.hs:209:54: warning: [GHC-63394] [-Wx-partial]
    In the use of ‘head’
    (imported from XMonad.Prelude, but defined in GHC.List):
    "This is a partial function, it throws an error on empty lists. Use pattern matching or Data.List.uncons instead. Consider refactoring to use Data.List.NonEmpty."
    |
209 |       defaultGroups = fromJust $ singletonZ $ G (ID (head ids) $ baseLayout g) emptyZ
    |                                                      ^^^^

XMonad/Layout/Groups.hs:226:61: warning: [GHC-63394] [-Wx-partial]
    In the use of ‘head’
    (imported from XMonad.Prelude, but defined in GHC.List):
    "This is a partial function, it throws an error on empty lists. Use pattern matching or Data.List.uncons instead. Consider refactoring to use Data.List.NonEmpty."
    |
226 |                                         >>> addWindows (ID (head ids) $ baseLayout g)
    |                                                             ^^^^

XMonad/Layout/Groups.hs:383:43: warning: [GHC-63394] [-Wx-partial]
    In the use of ‘head’
    (imported from XMonad.Prelude, but defined in GHC.List):
    "This is a partial function, it throws an error on empty lists. Use pattern matching or Data.List.uncons instead. Consider refactoring to use Data.List.NonEmpty."
    |
383 |         g' = flip modifyGroups g $ f (ID (head ids) $ baseLayout g)
    |                                           ^^^^

XMonad/Layout/Groups.hs:385:57: warning: [GHC-63394] [-Wx-partial]
    In the use of ‘tail’
    (imported from XMonad.Prelude, but defined in GHC.List):
    "This is a partial function, it throws an error on empty lists. Replace it with drop 1, or use pattern matching or Data.List.uncons instead. Consider refactoring to use Data.List.NonEmpty."
    |
385 |                                    >>> foldr (reID g) ((tail ids, []), [])
    |                                                         ^^^^

XMonad/Layout/Groups.hs:395:41: warning: [GHC-63394] [-Wx-partial]
    In the use of ‘head’
    (imported from XMonad.Prelude, but defined in GHC.List):
    "This is a partial function, it throws an error on empty lists. Use pattern matching or Data.List.uncons instead. Consider refactoring to use Data.List.NonEmpty."
    |
395 |     g' <- flip modifyGroupsX g $ f (ID (head ids) $ baseLayout g)
    |                                         ^^^^

XMonad/Layout/Groups.hs:397:60: warning: [GHC-63394] [-Wx-partial]
    In the use of ‘tail’
    (imported from XMonad.Prelude, but defined in GHC.List):
    "This is a partial function, it throws an error on empty lists. Replace it with drop 1, or use pattern matching or Data.List.uncons instead. Consider refactoring to use Data.List.NonEmpty."
    |
397 |                                 >>> fmap (foldr (reID g) ((tail ids, []), []))
    |                                                            ^^^^

XMonad/Layout/Groups/Helpers.hs:158:31: warning: [GHC-63394] [-Wx-partial]
    In the use of ‘tail’
    (imported from Prelude, but defined in GHC.List):
    "This is a partial function, it throws an error on empty lists. Replace it with drop 1, or use pattern matching or Data.List.uncons instead. Consider refactoring to use Data.List.NonEmpty."
    |
158 |                  let (before, tail -> after) = span (/=w) ws
    |                               ^^^^

XMonad/Actions/WorkspaceCursors.hs:53:47: warning: [GHC-38856] [-Wunused-imports]
    The import of ‘liftA2’ from module ‘XMonad.Prelude’ is redundant
   |
53 | import XMonad.Prelude (find, fromJust, guard, liftA2, toList, when, (<=<))
   |                                               ^^^^^^

XMonad/Actions/WorkspaceCursors.hs:100:34: warning: [GHC-63394] [-Wx-partial]
    In the use of ‘head’
    (imported from Prelude, but defined in GHC.List):
    "This is a partial function, it throws an error on empty lists. Use pattern matching or Data.List.uncons instead. Consider refactoring to use Data.List.NonEmpty."
    |
100 |     where x = end $ map return $ head a
    |                                  ^^^^

XMonad/Actions/WorkspaceCursors.hs:101:35: warning: [GHC-63394] [-Wx-partial]
    In the use of ‘tail’
    (imported from Prelude, but defined in GHC.List):
    "This is a partial function, it throws an error on empty lists. Replace it with drop 1, or use pattern matching or Data.List.uncons instead. Consider refactoring to use Data.List.NonEmpty."
    |
101 |           xs = map (map return) $ tail a
    |                                   ^^^^

XMonad/Util/Timer.hs:56:43: warning: [GHC-63394] [-Wx-partial]
    In the use of ‘head’
    (imported from Prelude, but defined in GHC.List):
    "This is a partial function, it throws an error on empty lists. Use pattern matching or Data.List.uncons instead. Consider refactoring to use Data.List.NonEmpty."
   |
56 |   if mt == a && dt /= [] && fromIntegral (head dt) == ti
   |                                           ^^^^

XMonad/Layout/Dwindle.hs:162:19: warning: [GHC-63394] [-Wx-partial]
    In the use of ‘tail’
    (imported from Prelude, but defined in GHC.List):
    "This is a partial function, it throws an error on empty lists. Replace it with drop 1, or use pattern matching or Data.List.uncons instead. Consider refactoring to use Data.List.NonEmpty."
    |
162 |         totals  = tail totals'
    |                   ^^^^

XMonad/Layout/Dwindle.hs:163:24: warning: [GHC-63394] [-Wx-partial]
    In the use of ‘tail’
    (imported from Prelude, but defined in GHC.List):
    "This is a partial function, it throws an error on empty lists. Replace it with drop 1, or use pattern matching or Data.List.uncons instead. Consider refactoring to use Data.List.NonEmpty."
    |
163 |         splits  = zip (tail sizes) totals
    |                        ^^^^

XMonad/Hooks/Place.hs:196:49: warning: [GHC-63394] [-Wx-partial]
    In the use of ‘head’
    (imported from XMonad.Prelude, but defined in GHC.List):
    "This is a partial function, it throws an error on empty lists. Use pattern matching or Data.List.uncons instead. Consider refactoring to use Data.List.NonEmpty."
    |
196 |                       let (workspace, screen) = head infos
    |                                                 ^^^^

XMonad/Prompt.hs:537:21: warning: [GHC-63394] [-Wx-partial]
    In the use of ‘head’
    (imported from XMonad.Prelude, but defined in GHC.List):
    "This is a partial function, it throws an error on empty lists. Use pattern matching or Data.List.uncons instead. Consider refactoring to use Data.List.NonEmpty."
    |
537 |   let defaultMode = head modes
    |                     ^^^^

XMonad/Prompt.hs:540:38: warning: [GHC-63394] [-Wx-partial]
    In the use of ‘tail’
    (imported from XMonad.Prelude, but defined in GHC.List):
    "This is a partial function, it throws an error on empty lists. Replace it with drop 1, or use pattern matching or Data.List.uncons instead. Consider refactoring to use Data.List.NonEmpty."
    |
540 |                           , W.down = tail modes -- Other modes
    |                                      ^^^^

XMonad/Prompt.hs:646:50: warning: [GHC-63394] [-Wx-partial]
    In the use of ‘tail’
    (imported from XMonad.Prelude, but defined in GHC.List):
    "This is a partial function, it throws an error on empty lists. Replace it with drop 1, or use pattern matching or Data.List.uncons instead. Consider refactoring to use Data.List.NonEmpty."
    |
646 |                 modify $ \s -> s { eventBuffer = tail l }
    |                                                  ^^^^

XMonad/Prompt.hs:647:26: warning: [GHC-63394] [-Wx-partial]
    In the use of ‘head’
    (imported from XMonad.Prelude, but defined in GHC.List):
    "This is a partial function, it throws an error on empty lists. Use pattern matching or Data.List.uncons instead. Consider refactoring to use Data.List.NonEmpty."
    |
647 |                 return $ head l
    |                          ^^^^

XMonad/Prompt.hs:779:76: warning: [GHC-63394] [-Wx-partial]
    In the use of ‘head’
    (imported from XMonad.Prelude, but defined in GHC.List):
    "This is a partial function, it throws an error on empty lists. Use pattern matching or Data.List.uncons instead. Consider refactoring to use Data.List.NonEmpty."
    |
779 |               if command st == hlCompl then put st else replaceCompletion (head cs)
    |                                                                            ^^^^

XMonad/Prompt.hs:1302:51: warning: [GHC-63394] [-Wx-partial]
    In the use of ‘tail’
    (imported from XMonad.Prelude, but defined in GHC.List):
    "This is a partial function, it throws an error on empty lists. Replace it with drop 1, or use pattern matching or Data.List.uncons instead. Consider refactoring to use Data.List.NonEmpty."
     |
1302 |             | oo <  length oc && d == Next = f ++ tail ss
     |                                                   ^^^^

XMonad/Prompt.hs:1386:13: warning: [GHC-63394] [-Wx-partial]
    In the use of ‘head’
    (imported from XMonad.Prelude, but defined in GHC.List):
    "This is a partial function, it throws an error on empty lists. Use pattern matching or Data.List.uncons instead. Consider refactoring to use Data.List.NonEmpty."
     |
1386 |     let c = head s
     |             ^^^^

XMonad/Prompt.hs:1510:38: warning: [GHC-63394] [-Wx-partial]
    In the use of ‘head’
    (imported from XMonad.Prelude, but defined in GHC.List):
    "This is a partial function, it throws an error on empty lists. Use pattern matching or Data.List.uncons instead. Consider refactoring to use Data.List.NonEmpty."
     |
1510 |                       in (prt ++ a, [head b], tail b)
     |                                      ^^^^

XMonad/Prompt.hs:1510:47: warning: [GHC-63394] [-Wx-partial]
    In the use of ‘tail’
    (imported from XMonad.Prelude, but defined in GHC.List):
    "This is a partial function, it throws an error on empty lists. Replace it with drop 1, or use pattern matching or Data.List.uncons instead. Consider refactoring to use Data.List.NonEmpty."
     |
1510 |                       in (prt ++ a, [head b], tail b)
     |                                               ^^^^

XMonad/Prompt.hs:1594:43: warning: [GHC-63394] [-Wx-partial]
    In the use of ‘head’
    (imported from XMonad.Prelude, but defined in GHC.List):
    "This is a partial function, it throws an error on empty lists. Use pattern matching or Data.List.uncons instead. Consider refactoring to use Data.List.NonEmpty."
     |
1594 |   (asc, desc) <- io $ textExtentsXMF fs $ head compl
     |                                           ^^^^

XMonad/Prompt.hs:1767:40: warning: [GHC-63394] [-Wx-partial]
    In the use of ‘tail’
    (imported from XMonad.Prelude, but defined in GHC.List):
    "This is a partial function, it throws an error on empty lists. Replace it with drop 1, or use pattern matching or Data.List.uncons instead. Consider refactoring to use Data.List.NonEmpty."
     |
1767 |             (s1',s2') = breakAtSpace $ tail s2
     |                                        ^^^^

XMonad/Prompt.hs:1795:25: warning: [GHC-63394] [-Wx-partial]
    In the use of ‘head’
    (imported from XMonad.Prelude, but defined in GHC.List):
    "This is a partial function, it throws an error on empty lists. Use pattern matching or Data.List.uncons instead. Consider refactoring to use Data.List.NonEmpty."
     |
1795 | deleteConsecutive = map head . group
     |                         ^^^^

XMonad/Prompt/Shell.hs:200:44: warning: [GHC-63394] [-Wx-partial]
    In the use of ‘head’
    (imported from XMonad.Prelude, but defined in GHC.List):
    "This is a partial function, it throws an error on empty lists. Use pattern matching or Data.List.uncons instead. Consider refactoring to use Data.List.NonEmpty."
    |
200 |     return . uniqSort . filter ((/= '.') . head) . concat $ es
    |                                            ^^^^

XMonad/Actions/WindowGo.hs:93:70: warning: [GHC-63394] [-Wx-partial]
    In the use of ‘head’
    (imported from XMonad.Prelude, but defined in GHC.List):
    "This is a partial function, it throws an error on empty lists. Use pattern matching or Data.List.uncons instead. Consider refactoring to use Data.List.NonEmpty."
   |
93 | ifWindow qry mh = ifWindows qry (windows . appEndo <=< runQuery mh . head)
   |                                                                      ^^^^

XMonad/Actions/WindowGo.hs:168:30: warning: [GHC-63394] [-Wx-partial]
    In the use of ‘head’
    (imported from XMonad.Prelude, but defined in GHC.List):
    "This is a partial function, it throws an error on empty lists. Use pattern matching or Data.List.uncons instead. Consider refactoring to use Data.List.NonEmpty."
    |
168 |     _ -> windows . focusFn . head $ ws
    |                              ^^^^

XMonad/Prompt/RunOrRaise.hs:25:47: warning: [GHC-38856] [-Wunused-imports]
    The import of ‘liftA2’ from module ‘XMonad.Prelude’ is redundant
   |
25 | import XMonad.Prelude (isNothing, isSuffixOf, liftA2)
   |                                               ^^^^^^

XMonad/Prompt/OrgMode.hs:528:26: warning: [GHC-63394] [-Wx-partial]
    In the use of ‘head’
    (imported from XMonad.Prelude, but defined in GHC.List):
    "This is a partial function, it throws an error on empty lists. Use pattern matching or Data.List.uncons instead. Consider refactoring to use Data.List.NonEmpty."
    |
528 |       str  <- munch  (/= head ptn)
    |                          ^^^^

XMonad/Layout/LayoutBuilder.hs:460:45: warning: [GHC-63394] [-Wx-partial]
    In the use of ‘tail’
    (imported from Prelude, but defined in GHC.List):
    "This is a partial function, it throws an error on empty lists. Replace it with drop 1, or use pattern matching or Data.List.uncons instead. Consider refactoring to use Data.List.NonEmpty."
    |
460 |                                 , W.down  = tail $ dropWhile (/=f) w
    |                                             ^^^^

XMonad/Hooks/StatusBar/PP.hs:404:16: warning: [GHC-63394] [-Wx-partial]
    In the use of ‘head’
    (imported from XMonad.Prelude, but defined in GHC.List):
    "This is a partial function, it throws an error on empty lists. Use pattern matching or Data.List.uncons instead. Consider refactoring to use Data.List.NonEmpty."
    |
404 |       | '^' == head x       = strip keep (drop 1 . dropWhile (/= ')') $ x)
    |                ^^^^

XMonad/Hooks/StatusBar/PP.hs:467:14: warning: [GHC-63394] [-Wx-partial]
    In the use of ‘head’
    (imported from XMonad.Prelude, but defined in GHC.List):
    "This is a partial function, it throws an error on empty lists. Use pattern matching or Data.List.uncons instead. Consider refactoring to use Data.List.NonEmpty."
    |
467 |     in fst $ head $ dropWhile (uncurry (/=)) $ zip xs $ tail xs
    |              ^^^^

XMonad/Hooks/StatusBar/PP.hs:467:57: warning: [GHC-63394] [-Wx-partial]
    In the use of ‘tail’
    (imported from XMonad.Prelude, but defined in GHC.List):
    "This is a partial function, it throws an error on empty lists. Replace it with drop 1, or use pattern matching or Data.List.uncons instead. Consider refactoring to use Data.List.NonEmpty."
    |
467 |     in fst $ head $ dropWhile (uncurry (/=)) $ zip xs $ tail xs
    |                                                         ^^^^

XMonad/Hooks/Minimize.hs:47:36: warning: [GHC-63394] [-Wx-partial]
    In the use of ‘head’
    (imported from XMonad.Prelude, but defined in GHC.List):
    "This is a partial function, it throws an error on empty lists. Use pattern matching or Data.List.uncons instead. Consider refactoring to use Data.List.NonEmpty."
   |
47 |       let message = fromIntegral . head $ dt
   |                                    ^^^^

XMonad/Util/ExclusiveScratchpads.hs:42:42: warning: [GHC-38856] [-Wunused-imports]
    The import of ‘liftA2’ from module ‘XMonad.Prelude’ is redundant
   |
42 | import XMonad.Prelude (appEndo, filterM, liftA2, (<=<))
   |                                          ^^^^^^

XMonad/Util/ExclusiveScratchpads.hs:177:11: warning: [GHC-63394] [-Wx-partial]
    In the use of ‘head’
    (imported from Prelude, but defined in GHC.List):
    "This is a partial function, it throws an error on empty lists. Use pattern matching or Data.List.uncons instead. Consider refactoring to use Data.List.NonEmpty."
    |
177 |     mh <- head . map hook <$> ys  -- ys /= [], so `head` is fine
    |           ^^^^

XMonad/Util/ExclusiveScratchpads.hs:178:11: warning: [GHC-63394] [-Wx-partial]
    In the use of ‘head’
    (imported from Prelude, but defined in GHC.List):
    "This is a partial function, it throws an error on empty lists. Use pattern matching or Data.List.uncons instead. Consider refactoring to use Data.List.NonEmpty."
    |
178 |     n  <- head . map name <$> ys  -- same
    |           ^^^^

XMonad/Layout/ComboP.hs:187:63: warning: [GHC-63394] [-Wx-partial]
    In the use of ‘tail’
    (imported from XMonad.Prelude, but defined in GHC.List):
    "This is a partial function, it throws an error on empty lists. Replace it with drop 1, or use pattern matching or Data.List.uncons instead. Consider refactoring to use Data.List.NonEmpty."
    |
187 |                                                      , down = tail $ dropWhile (/=z) xs }
    |                                                               ^^^^

XMonad/Layout/Combo.hs:91:69: warning: [GHC-63394] [-Wx-partial]
    In the use of ‘head’
    (imported from Prelude, but defined in GHC.List):
    "This is a partial function, it throws an error on empty lists. Use pattern matching or Data.List.uncons instead. Consider refactoring to use Data.List.NonEmpty."
   |
91 |                   do let w2' = case origws `intersect` w2 of [] -> [head origws]
   |                                                                     ^^^^

XMonad/Layout/Combo.hs:124:63: warning: [GHC-63394] [-Wx-partial]
    In the use of ‘head’
    (imported from Prelude, but defined in GHC.List):
    "This is a partial function, it throws an error on empty lists. Use pattern matching or Data.List.uncons instead. Consider refactoring to use Data.List.NonEmpty."
    |
124 |                                                  (maybe super head msuper')
    |                                                               ^^^^

XMonad/Layout/Combo.hs:125:60: warning: [GHC-63394] [-Wx-partial]
    In the use of ‘head’
    (imported from Prelude, but defined in GHC.List):
    "This is a partial function, it throws an error on empty lists. Use pattern matching or Data.List.uncons instead. Consider refactoring to use Data.List.NonEmpty."
    |
125 |                                                  (maybe l1 head ml1')
    |                                                            ^^^^

XMonad/Layout/Combo.hs:126:60: warning: [GHC-63394] [-Wx-partial]
    In the use of ‘head’
    (imported from Prelude, but defined in GHC.List):
    "This is a partial function, it throws an error on empty lists. Use pattern matching or Data.List.uncons instead. Consider refactoring to use Data.List.NonEmpty."
    |
126 |                                                  (maybe l2 head ml2')
    |                                                            ^^^^

XMonad/Layout/Combo.hs:135:63: warning: [GHC-63394] [-Wx-partial]
    In the use of ‘tail’
    (imported from Prelude, but defined in GHC.List):
    "This is a partial function, it throws an error on empty lists. Replace it with drop 1, or use pattern matching or Data.List.uncons instead. Consider refactoring to use Data.List.NonEmpty."
    |
135 |                                                      , down = tail $ dropWhile (/=z) xs }
    |                                                               ^^^^

XMonad/Layout/TallMastersCombo.hs:247:61: warning: [GHC-63394] [-Wx-partial]
    In the use of ‘head’
    (imported from Prelude, but defined in GHC.List):
    "This is a partial function, it throws an error on empty lists. Use pattern matching or Data.List.uncons instead. Consider refactoring to use Data.List.NonEmpty."
    |
247 |         let subMaster = if null w2 then Nothing else Just $ head w2
    |                                                             ^^^^

XMonad/Layout/TallMastersCombo.hs:254:61: warning: [GHC-63394] [-Wx-partial]
    In the use of ‘head’
    (imported from Prelude, but defined in GHC.List):
    "This is a partial function, it throws an error on empty lists. Use pattern matching or Data.List.uncons instead. Consider refactoring to use Data.List.NonEmpty."
    |
254 |         let subMaster = if null w2 then Nothing else Just $ head w2
    |                                                             ^^^^

XMonad/Layout/TallMastersCombo.hs:314:63: warning: [GHC-63394] [-Wx-partial]
    In the use of ‘tail’
    (imported from Prelude, but defined in GHC.List):
    "This is a partial function, it throws an error on empty lists. Replace it with drop 1, or use pattern matching or Data.List.uncons instead. Consider refactoring to use Data.List.NonEmpty."
    |
314 |                                                      , down = tail $ dropWhile (/=z) xs }
    |                                                               ^^^^

XMonad/Actions/GridSelect.hs:661:61: warning: [GHC-63394] [-Wx-partial]
    In the use of ‘head’
    (imported from XMonad.Prelude, but defined in GHC.List):
    "This is a partial function, it throws an error on empty lists. Use pattern matching or Data.List.uncons instead. Consider refactoring to use Data.List.NonEmpty."
    |
661 |                                 s = TwoDState { td_curpos = head coords,
    |                                                             ^^^^

XMonad/Util/EZConfig.hs:441:23: warning: [GHC-63394] [-Wx-partial]
    In the use of ‘head’
    (imported from XMonad.Prelude, but defined in GHC.List):
    "This is a partial function, it throws an error on empty lists. Use pattern matching or Data.List.uncons instead. Consider refactoring to use Data.List.NonEmpty."
    |
441 |         combine ks = (head . fst . head $ ks,
    |                       ^^^^

XMonad/Util/EZConfig.hs:441:36: warning: [GHC-63394] [-Wx-partial]
    In the use of ‘head’
    (imported from XMonad.Prelude, but defined in GHC.List):
    "This is a partial function, it throws an error on empty lists. Use pattern matching or Data.List.uncons instead. Consider refactoring to use Data.List.NonEmpty."
    |
441 |         combine ks = (head . fst . head $ ks,
    |                                    ^^^^

XMonad/Util/EZConfig.hs:442:59: warning: [GHC-63394] [-Wx-partial]
    In the use of ‘tail’
    (imported from XMonad.Prelude, but defined in GHC.List):
    "This is a partial function, it throws an error on empty lists. Replace it with drop 1, or use pattern matching or Data.List.uncons instead. Consider refactoring to use Data.List.NonEmpty."
    |
442 |                       subm . mkSubmaps' subm $ map (first tail) ks)
    |                                                           ^^^^

XMonad/Util/EZConfig.hs:443:29: warning: [GHC-63394] [-Wx-partial]
    In the use of ‘head’
    (imported from XMonad.Prelude, but defined in GHC.List):
    "This is a partial function, it throws an error on empty lists. Use pattern matching or Data.List.uncons instead. Consider refactoring to use Data.List.NonEmpty."
    |
443 |         fstKey = (==) `on` (head . fst)
    |                             ^^^^

XMonad/Util/EZConfig.hs:547:27: warning: [GHC-63394] [-Wx-partial]
    In the use of ‘head’
    (imported from XMonad.Prelude, but defined in GHC.List):
    "This is a partial function, it throws an error on empty lists. Use pattern matching or Data.List.uncons instead. Consider refactoring to use Data.List.NonEmpty."
    |
547 |         dups = map (snd . head)
    |                           ^^^^

XMonad/Actions/Navigation2D.hs:786:14: warning: [GHC-63394] [-Wx-partial]
    In the use of ‘tail’
    (imported from Data.List, but defined in GHC.List):
    "This is a partial function, it throws an error on empty lists. Replace it with drop 1, or use pattern matching or Data.List.uncons instead. Consider refactoring to use Data.List.NonEmpty."
    |
786 |     onCtr' = L.tail $ L.dropWhile ((cur /=) . fst) onCtr
    |              ^^^^^^

XMonad/Actions/Navigation2D.hs:887:38: warning: [GHC-63394] [-Wx-partial]
    In the use of ‘head’
    (imported from XMonad.Prelude, but defined in GHC.List):
    "This is a partial function, it throws an error on empty lists. Use pattern matching or Data.List.uncons instead. Consider refactoring to use Data.List.NonEmpty."
    |
887 |     newwinset = winset { W.current = head newscrs
    |                                      ^^^^

XMonad/Actions/Navigation2D.hs:888:38: warning: [GHC-63394] [-Wx-partial]
    In the use of ‘tail’
    (imported from XMonad.Prelude, but defined in GHC.List):
    "This is a partial function, it throws an error on empty lists. Replace it with drop 1, or use pattern matching or Data.List.uncons instead. Consider refactoring to use Data.List.NonEmpty."
    |
888 |                        , W.visible = tail newscrs
    |                                      ^^^^

XMonad/Actions/Prefix.hs:169:37: warning: [GHC-63394] [-Wx-partial]
    In the use of ‘head’
    (imported from XMonad.Prelude, but defined in GHC.List):
    "This is a partial function, it throws an error on empty lists. Use pattern matching or Data.List.uncons instead. Consider refactoring to use Data.List.NonEmpty."
    |
169 |               Raw a -> replicate a (head events) ++ [key]
    |                                     ^^^^

XMonad/Actions/ShowText.hs:91:44: warning: [GHC-63394] [-Wx-partial]
    In the use of ‘head’
    (imported from Prelude, but defined in GHC.List):
    "This is a partial function, it throws an error on empty lists. Use pattern matching or Data.List.uncons instead. Consider refactoring to use Data.List.NonEmpty."
   |
91 |          (whenJust (lookup (fromIntegral $ head d) m) deleteWindow)
   |                                            ^^^^

XMonad/Actions/EasyMotion.hs:390:35: warning: [GHC-63394] [-Wx-partial]
    In the use of ‘tail’
    (imported from XMonad.Prelude, but defined in GHC.List):
    "This is a partial function, it throws an error on empty lists. Replace it with drop 1, or use pattern matching or Data.List.uncons instead. Consider refactoring to use Data.List.NonEmpty."
    |
390 |     trim = map (\o -> o { chord = tail $ chord o })
    |                                   ^^^^

[geekosaur]

There turn out to be a few in the core as well, I'll create an issue for that.