From 3f679480d356be30c912f3b971f3034e2cd9cb95 Mon Sep 17 00:00:00 2001
From: Samuel Pilz <samuel.pilz@posteo.net>
Date: Fri, 26 Jul 2019 11:22:43 +0200
Subject: [PATCH 1/2] fail installation if cabal-version is too low

---
 install/src/Cabal.hs | 13 ++++++-------
 1 file changed, 6 insertions(+), 7 deletions(-)

diff --git a/install/src/Cabal.hs b/install/src/Cabal.hs
index c09527505..f92fc7d89 100644
--- a/install/src/Cabal.hs
+++ b/install/src/Cabal.hs
@@ -56,15 +56,14 @@ cabalInstallHie versionNumber = do
 installCabal :: Action ()
 installCabal = do
   -- try to find existing `cabal` executable with appropriate version
-  cabalExe <- liftIO (findExecutable "cabal") >>= \case
-    Nothing       -> return Nothing
-    Just cabalExe -> do
-      cabalVersion <- trimmedStdout <$> execCabal ["--numeric-version"]
-      whenMaybe (checkVersion requiredCabalVersion cabalVersion)
-        $ return cabalExe
+  cabalExeOk <- liftIO (findExecutable "cabal") >>= \case
+    Nothing -> return False
+    Just _  -> do
+      checkCabal
+      return True
 
   -- install `cabal-install` if not already installed
-  when (isNothing cabalExe) $ execStackShake_ ["install", "cabal-install"]
+  unless cabalExeOk $ execStackShake_ ["install", "cabal-install"]
 
 -- | check `stack` has the required version
 checkCabal :: Action ()

From 6b5776e79a17a31334750097e7d53bb135b78466 Mon Sep 17 00:00:00 2001
From: Samuel Pilz <samuel.pilz@posteo.net>
Date: Fri, 26 Jul 2019 11:40:08 +0200
Subject: [PATCH 2/2] reafactor cabal-version-check in install script

---
 install/src/Cabal.hs | 15 ++++++++-------
 1 file changed, 8 insertions(+), 7 deletions(-)

diff --git a/install/src/Cabal.hs b/install/src/Cabal.hs
index f92fc7d89..ee79a9de8 100644
--- a/install/src/Cabal.hs
+++ b/install/src/Cabal.hs
@@ -4,7 +4,9 @@ import           Development.Shake
 import           Development.Shake.Command
 import           Development.Shake.FilePath
 import           Control.Monad
-import           Data.Maybe                               ( isNothing )
+import           Data.Maybe                               ( isNothing
+                                                          , isJust
+                                                          )
 import           Control.Monad.Extra                      ( whenMaybe )
 import           System.Directory                         ( findExecutable
                                                           , copyFile
@@ -56,11 +58,10 @@ cabalInstallHie versionNumber = do
 installCabal :: Action ()
 installCabal = do
   -- try to find existing `cabal` executable with appropriate version
-  cabalExeOk <- liftIO (findExecutable "cabal") >>= \case
-    Nothing -> return False
-    Just _  -> do
-      checkCabal
-      return True
+  cabalExeOk <- do
+    c <- liftIO (findExecutable "cabal")
+    when (isJust c) checkCabal
+    return $ isJust c
 
   -- install `cabal-install` if not already installed
   unless cabalExeOk $ execStackShake_ ["install", "cabal-install"]
@@ -68,7 +69,7 @@ installCabal = do
 -- | check `stack` has the required version
 checkCabal :: Action ()
 checkCabal = do
-  cabalVersion <- trimmedStdout <$> execCabal ["--numeric-version"]
+  cabalVersion <- getCabalVersion
   unless (checkVersion requiredCabalVersion cabalVersion) $ do
     printInStars $ cabalInstallIsOldFailMsg cabalVersion
     error $ stackExeIsOldFailMsg cabalVersion