ci: Drop support for GHC 8.4

Debian stable is not on 8.6, which was always our guide as to which GHC
versions we want to support.

In particular, this lets us get rid of all the quickcheck-classes
special treatment.

Related: 400730fe3b

.github/workflows/haskell-ci.yml

@@ -66,11 +66,6 @@ jobs:
             compilerVersion: 8.6.5
             setup-method: hvr-ppa
             allow-failure: false
-          - compiler: ghc-8.4.4
-            compilerKind: ghc
-            compilerVersion: 8.4.4
-            setup-method: hvr-ppa
-            allow-failure: false
       fail-fast: false
     steps:
       - name: apt

.github/workflows/stack.yml

@@ -12,7 +12,6 @@ jobs:
       fail-fast: false
       matrix:
         include:
-          - resolver: lts-12  # GHC 8.4
           - resolver: lts-14  # GHC 8.6
           - resolver: lts-16  # GHC 8.8
           - resolver: lts-18  # GHC 8.10

stack.yaml

@@ -6,13 +6,6 @@ packages:
 extra-deps:
 - X11-1.10
 
-flags:
-  xmonad:
-    # stack doesn't support automatic flags
-    # https://cabal.readthedocs.io/en/latest/cabal-package.html#resolution-of-conditions-and-flags
-    # https://github.com/commercialhaskell/stack/issues/1313#issuecomment-157259270
-    quickcheck-classes: false
-
 nix:
   packages:
     - zlib

tests/Properties/Stack.hs

@@ -1,9 +1,5 @@
-{-# LANGUAGE CPP #-}
 {-# LANGUAGE ScopedTypeVariables #-}
-
-#ifdef VERSION_quickcheck_classes
 {-# LANGUAGE GeneralizedNewtypeDeriving #-}
-#endif
 
 module Properties.Stack where
 
@@ -15,13 +11,11 @@ import qualified XMonad.StackSet as S (filter)
 
 import Data.Maybe
 
-#ifdef VERSION_quickcheck_classes
 import Data.Proxy
 import Test.QuickCheck.Classes (
     Laws (lawsTypeclass, lawsProperties), Proxy1 (Proxy1),
     foldableLaws, traversableLaws,
     )
-#endif
 
 
 -- The list returned by index should be the same length as the actual
@@ -65,7 +59,6 @@ prop_differentiate xs =
     where _ = xs :: [Int]
 
 
-#ifdef VERSION_quickcheck_classes
 -- Check type class laws of 'Data.Foldable.Foldable' and 'Data.Traversable.Traversable'.
 newtype TestStack a = TestStack (Stack a)
     deriving (Eq, Read, Show, Foldable, Functor)
@@ -82,6 +75,3 @@ prop_laws_Stack = format (foldableLaws p) <> format (traversableLaws p)
     p = Proxy :: Proxy TestStack
     format laws = [ ("Stack: " <> lawsTypeclass laws <> ": " <> name, prop)
                   | (name, prop) <- lawsProperties laws ]
-#else
-prop_laws_Stack = []
-#endif

xmonad.cabal

@@ -27,7 +27,7 @@ author:             Spencer Janssen, Don Stewart, Adam Vogt, David Roundy, Jason
                     Ondřej Súkup, Paul Hebble, Shachaf Ben-Kiki, Siim Põder, Tim McIver,
                     Trevor Elliott, Wouter Swierstra, Conrad Irwin, Tim Thelion, Tony Zorman
 maintainer:         xmonad@haskell.org
-tested-with:        GHC == 8.4.4 || == 8.6.5 || == 8.8.4 || == 8.10.7 || == 9.0.2 || == 9.2.5 || == 9.4.2
+tested-with:        GHC == 8.6.5 || == 8.8.4 || == 8.10.7 || == 9.0.2 || == 9.2.5 || == 9.4.2
 category:           System
 homepage:           http://xmonad.org
 bug-reports:        https://github.com/xmonad/xmonad/issues
@@ -54,8 +54,6 @@ flag pedantic
   default:     False
   manual:      True
 
-flag quickcheck-classes
-
 library
   exposed-modules: XMonad
                    XMonad.Config
@@ -83,7 +81,7 @@ library
   default-language: Haskell2010
 
   -- Keep this in sync with the oldest version in 'tested-with'
-  if impl(ghc > 8.4.4)
+  if impl(ghc > 8.6.5)
     ghc-options:   -Wno-unused-imports
 
   if flag(pedantic)
@@ -96,7 +94,7 @@ executable xmonad
   default-language: Haskell2010
 
   -- Keep this in sync with the oldest version in 'tested-with'
-  if impl(ghc > 8.4.4)
+  if impl(ghc > 8.6.5)
     ghc-options:   -Wno-unused-imports
 
   if flag(pedantic)
@@ -125,15 +123,11 @@ test-suite properties
   hs-source-dirs: tests
   build-depends:  base
                 , QuickCheck >= 2
+                , quickcheck-classes >= 0.4.3
                 , X11
                 , containers
                 , xmonad
   default-language: Haskell2010
 
-  if flag(quickcheck-classes) && impl(ghc > 8.5)
-    -- no quickcheck-classes in LTS-12
-    -- GHC 8.4 and lower needs too much boilerplate (Eq1, Show1, …)
-    build-depends: quickcheck-classes >= 0.4.3
-
   if flag(pedantic)
     ghc-options:   -Werror