testsuite: Set TMPDIR to a specific folder rather than the test root

If things start getting created in the TMPDIR, then it is better to not
place them directly in the project root next to the source and test
files. This also makes it easier to write tests which are sensitive to
what is created in the CWD.

Author: mpickering

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

@@ -15,7 +15,7 @@ main = cabalTest $ recordMode DoNotRecord $ withProjectFile "cabal.project" $ do
           else "haddock-response*.txt"
 
   -- Check that there is a response file.
-  responseFiles <- assertGlobMatchesTestDir testTmpDir glob
+  responseFiles <- assertGlobMatchesTestDir testSystemTmpDir glob
 
   -- Check that the matched response file is not empty, and is indeed a Haddock
   -- response file.

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

@@ -22,7 +22,7 @@ main =
             else "haddock-response*.txt"
 
     -- Check that there is a response file.
-    responseFiles <- assertGlobMatchesTestDir testTmpDir glob
+    responseFiles <- assertGlobMatchesTestDir testSystemTmpDir glob
 
     -- Check that the matched response file is not empty, and is indeed a Haddock
     -- response file.

cabal-testsuite/src/Test/Cabal/Monad.hs

@@ -34,6 +34,7 @@ module Test.Cabal.Monad (
     testPrefixDir,
     testLibInstallDir,
     testDistDir,
+    testSystemTmpDir,
     testPackageDbDir,
     testRepoDir,
     testKeysDir,
@@ -407,9 +408,9 @@ runTestM mode m =
                         , ("CABAL_DIR", Just (testCabalDir env))
                         , ("CABAL_CONFIG", Just (testUserCabalConfigFile env))
                         -- Set `TMPDIR` so that temporary files aren't created in the global `TMPDIR`.
-                        , ("TMPDIR", Just tmp_dir)
+                        , ("TMPDIR", Just (testSystemTmpDir env))
                         -- Windows uses `TMP` for the `TMPDIR`.
-                        , ("TMP", Just tmp_dir)
+                        , ("TMP", Just (testSystemTmpDir env))
                         ],
                     testShouldFail = False,
                     testRelativeCurrentDir = ".",
@@ -548,6 +549,7 @@ initWorkDir :: TestM ()
 initWorkDir = do
     env <- getTestEnv
     liftIO $ createDirectoryIfMissing True (testWorkDir env)
+    liftIO $ createDirectoryIfMissing True (testSystemTmpDir env)
 
 
 
@@ -824,6 +826,11 @@ testName env = testSubName env <.> testMode env
 testWorkDir :: TestEnv -> FilePath
 testWorkDir env = testTmpDir env </> (testName env <.> "dist")
 
+-- The folder which TMPDIR is set to.
+-- This is different to testTmpDir, which is the folder which is the test is run from.
+testSystemTmpDir :: TestEnv -> FilePath
+testSystemTmpDir env = testWorkDir env </> "tmp"
+
 -- | The absolute prefix where installs go.
 testPrefixDir :: TestEnv -> FilePath
 testPrefixDir env = testWorkDir env </> "usr"