ci: Test with older GHC versions

This should give us a warning that we need to bump the base lower bounds
if we ever break old GHCs again.

Related: #80

Author: liskin

.github/workflows/haskell-ci.yml

@@ -46,6 +46,12 @@ jobs:
             allow-failure: false
           - compiler: ghc-8.4.4
             allow-failure: false
+          - compiler: ghc-8.2.2
+            allow-failure: false
+          - compiler: ghc-8.0.2
+            allow-failure: false
+          - compiler: ghc-7.10.3
+            allow-failure: false
       fail-fast: false
     steps:
       - name: apt
@@ -146,8 +152,8 @@ jobs:
           touch cabal.project
           touch cabal.project.local
           echo "packages: ${PKGDIR_X11}" >> cabal.project
-          echo "package X11" >> cabal.project
-          echo "    ghc-options: -Werror=missing-methods" >> cabal.project
+          if [ $((HCNUMVER >= 80200)) -ne 0 ] ; then echo "package X11" >> cabal.project ; fi
+          if [ $((HCNUMVER >= 80200)) -ne 0 ] ; then echo "    ghc-options: -Werror=missing-methods" >> cabal.project ; fi
           cat >> cabal.project <<EOF
           package X11
             flags: +pedantic

X11.cabal

@@ -10,7 +10,7 @@ license-file:       LICENSE
 copyright:          Alastair Reid, 1999-2003, libraries@haskell.org 2003-2007,
                     Don Stewart 2007-2009, Spencer Janssen 2007-2009, Daniel Wagner 2009-2011.
 maintainer:         Daniel Wagner <daniel@wagner-home.com>
-tested-with:        GHC == 8.4.4 || == 8.6.5 || == 8.8.4 || == 8.10.4 || == 9.0.1
+tested-with:        GHC == 7.10.3 || == 8.0.2 || == 8.2.2 || == 8.4.4 || == 8.6.5 || == 8.8.4 || == 8.10.4 || == 9.0.1
 category:           Graphics
 homepage:           https://github.com/xmonad/X11
 bug-reports:        https://github.com/xmonad/X11/issues