Set CABAL_DIR in cabal-tests (fixes haskell#5187).

This change gives each test a new cabal directory on Windows and prevents the
tests from accessing the user's cabal directory.

This commit also re-enables
PackageTests/Regression/T4154/install-time-with-constraint.test.hs on Windows.

cabal-testsuite/PackageTests/CustomDep/cabal.test.hs

@@ -8,5 +8,5 @@ main = cabalTest $ do
     -- database, don't record the output
     recordMode DoNotRecord $ do
         -- TODO: Hack, delete me
-        withEnvFilter (/= "HOME") $ do
+        withEnvFilter (`notElem` ["HOME", "CABAL_DIR"]) $ do
             cabal "new-build" ["all"]

cabal-testsuite/PackageTests/CustomPlain/cabal.test.hs

@@ -5,7 +5,7 @@ main = cabalTest $ do
     -- Regression test for #4393
     recordMode DoNotRecord $ do
         -- TODO: Hack; see also CustomDep/cabal.test.hs
-        withEnvFilter (/= "HOME") $ do
+        withEnvFilter (`notElem` ["HOME", "CABAL_DIR"]) $ do
             -- On -v2, we don't have vQuiet set, which suppressed
             -- the error
             cabal "new-build" ["-v1"]

cabal-testsuite/PackageTests/Regression/T4154/install-time-with-constraint.test.hs

@@ -5,9 +5,6 @@ import Test.Cabal.Prelude
 -- building its setup script with the installed Cabal, which depends on the
 -- installed time, even though the installed time doesn't fit the constraint.
 main = cabalTest $ do
-  -- TODO: Run this test on Windows once #5187 is resolved.
-  skipIf =<< isWindows
-
   cabal "new-build" ["time", "--constraint=time==99999", "--dry-run"]
 
   -- Temporarily disabled recording here because output is not stable

cabal-testsuite/Test/Cabal/Monad.hs

@@ -31,12 +31,12 @@ module Test.Cabal.Monad (
     testPrefixDir,
     testDistDir,
     testPackageDbDir,
-    testHomeDir,
     testSandboxDir,
     testSandboxConfigFile,
     testRepoDir,
     testKeysDir,
     testSourceCopyDir,
+    testCabalDir,
     testUserCabalConfigFile,
     testActualFile,
     -- * Skipping tests
@@ -316,7 +316,10 @@ runTestM mode m = do
                         -- Try to avoid Unicode output
                         [ ("LC_ALL", Just "C")
                         -- Hermetic builds (knot-tied)
-                        , ("HOME", Just (testHomeDir env))],
+                        , ("HOME", Just (testHomeDir env))
+                        -- Set CABAL_DIR in addition to HOME, since HOME has no
+                        -- effect on Windows.
+                        , ("CABAL_DIR", Just (testCabalDir env))],
                     testShouldFail = False,
                     testRelativeCurrentDir = ".",
                     testHavePackageDb = False,
@@ -343,7 +346,7 @@ runTestM mode m = do
         -- the default configuration hardcodes Hackage, which we do
         -- NOT want to assume for these tests (no test should
         -- hit Hackage.)
-        liftIO $ createDirectoryIfMissing True (testHomeDir env </> ".cabal")
+        liftIO $ createDirectoryIfMissing True (testCabalDir env)
         ghc_path <- programPathM ghcProgram
         liftIO $ writeFile (testUserCabalConfigFile env)
                $ unlines [ "with-compiler: " ++ ghc_path ]
@@ -637,10 +640,13 @@ testKeysDir env = testWorkDir env </> "keys"
 testSourceCopyDir :: TestEnv -> FilePath
 testSourceCopyDir env = testWorkDir env </> "source"
 
+-- | The user cabal directory
+testCabalDir :: TestEnv -> FilePath
+testCabalDir env = testHomeDir env </> ".cabal"
+
 -- | The user cabal config file
--- TODO: Not obviously working on Windows
 testUserCabalConfigFile :: TestEnv -> FilePath
-testUserCabalConfigFile env = testHomeDir env </> ".cabal" </> "config"
+testUserCabalConfigFile env = testCabalDir env </> "config"
 
 -- | The file where the expected output of the test lives
 testExpectFile :: TestEnv -> FilePath

cabal-testsuite/Test/Cabal/Prelude.hs

@@ -512,7 +512,7 @@ withRepo repo_dir m = do
     hackageRepoTool "bootstrap" ["--keys", testKeysDir env, "--repo", testRepoDir env]
     -- 5. Wire it up in .cabal/config
     -- TODO: libify this
-    let package_cache = testHomeDir env </> ".cabal" </> "packages"
+    let package_cache = testCabalDir env </> "packages"
     liftIO $ appendFile (testUserCabalConfigFile env)
            $ unlines [ "repository test-local-repo"
                      , "  url: file:" ++ testRepoDir env