.github/workflows/ci.yml

-name: CI
-
-# Trigger the workflow on push or pull request, but only for the master branch
-on:
-  pull_request:
-  push:
-    branches: [master]
-
-jobs:
-  cabal:
-    name: ${{ matrix.os }} / ghc ${{ matrix.ghc }}
-    runs-on: ${{ matrix.os }}
-    strategy:
-      fail-fast: false
-      matrix:
-        os: [ubuntu-latest]
-        cabal: ["latest"]
-        ghc: ["8.6", "8.8", "8.10"]
-
-    steps:
-    - uses: actions/checkout@v2
-      if: github.event.action == 'opened' || github.event.action == 'synchronize' || github.event.ref == 'refs/heads/master'
-
-    - uses: actions/setup-haskell@v1.1
-      id: setup-haskell-cabal
-      name: Setup Haskell
-      with:
-        ghc-version: ${{ matrix.ghc }}
-        cabal-version: ${{ matrix.cabal }}
-
-    - name: Build
-      run: |
-        cabal update
-        cabal build all --enable-tests --enable-benchmarks --write-ghc-environment-files=always
-
-    - name: Test
-      run: |
-        cabal test all --enable-tests

test.hs

+{-# LANGUAGE LambdaCase #-}
+{-# LANGUAGE BlockArguments #-}
+
+module Main where
+
+import qualified Data.List as List
+import System.Process
+import Control.Monad
+import Data.Version
+import Text.ParserCombinators.ReadP
+
+main :: IO ()
+main = do
+  callCommand "ghcup upgrade"
+
+  let toVersion x = fst $ head $ filter (null . snd) $ readP_to_S (parseVersion) x
+  let show_versions = concatMap (\v -> "\n  - " ++ showVersion v)
+
+  -- get available GHC versions via ghcup
+  avails <- readCreateProcess (shell "ghcup list -r -t ghc") ""
+  let fix_avail = toVersion . takeWhile (/= ' ') . drop 4
+  let avail_ghc_versions = fmap fix_avail (lines avails)
+  putStrLn $ "Available GHC versions: " ++ show_versions avail_ghc_versions
+
+  let 
+    -- only test the recent ones
+    test_pred = (>= makeVersion [8,8])
+    prefiltered = filter test_pred avail_ghc_versions
+
+    -- take only the latest version per major release
+    major = take 2 . versionBranch
+    same_major x y = major x == major y
+    test_ghc_versions = fmap (last . List.sort) $ List.groupBy same_major prefiltered
+
+  putStrLn $ "We will test the following GHC versions: " ++ show_versions test_ghc_versions
+
+  forM_ test_ghc_versions \version -> do
+    let v   = showVersion version
+    let ghc = "ghc-"++v
+
+    putStrLn "#######################################"
+    putStrLn $ "Testing " ++ ghc
+    putStrLn "#######################################"
+    putStrLn "# Installing GHC..."
+    callCommand $ "ghcup install ghc " ++ v
+
+    putStrLn "# Trying to build with cabal-install..."
+    callCommand "cabal clean"
+    callCommand $ "cabal build -w " ++ ghc
+