Fix HaddockKeepTmpsCustom test for merge skew

The `HaddockKeepTmpsCustom` test added in haskell#10392 skewed against haskell#10366,
which changes where temporary files are written.

We can work around this by setting `$TMPDIR` and `$TEMP` while running
tests, so that temporary files are written to the test's temporary
directory rather than the system one.

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

@@ -11,11 +11,11 @@ main = cabalTest $ recordMode DoNotRecord $ withProjectFile "cabal.project" $ do
   --   "foobar.ext" will be "fooXXX.ext".
   let glob =
         if isWindows
-          then "**/had*.txt"
-          else "**/haddock-response*.txt"
+          then "had*.txt"
+          else "haddock-response*.txt"
 
   -- Check that there is a response file.
-  responseFiles <- assertGlobMatchesTestDir testDistDir glob
+  responseFiles <- assertGlobMatchesTestDir testTmpDir glob
 
   -- Check that the matched response file is not empty, and is indeed a Haddock
   -- response file.

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

@@ -1,23 +1,29 @@
-{-# LANGUAGE LambdaCase #-}
-import Test.Cabal.Prelude
-import Data.List (sort, isPrefixOf)
-import Distribution.Verbosity
+import Data.List (isPrefixOf, sort)
 import Distribution.Simple.Glob
 import Distribution.Simple.Glob.Internal
 import Distribution.Simple.Utils
+import Distribution.Verbosity
 import System.Directory
+import Test.Cabal.Prelude
 
 -- Test that "cabal haddock" preserves temporary files
 -- We use haddock-keep-temp-file: True in the cabal.project.
 main =
   cabalTest $ recordMode DoNotRecord $ withProjectFile "cabal.project" $ do
-      pwd <- testTmpDir <$> getTestEnv
-      liftIO $ createDirectory (pwd </> "temp")
-      withEnv [(if isWindows then "TMP" else "TMPDIR", Just $ pwd </> "temp")] $
-        cabal "haddock" []
-      files <- liftIO $ listDirectory (pwd </> "temp")
-      case [ pwd </> "temp" </> f | f <- files, takeExtension f == ".txt" ] of
-        [] -> error "Expecting a response file being mentioned in the outcome"
-        files' ->
-          -- Assert the matched response file is not empty, and indeed a haddock rsp
-          assertAnyFileContains files' "--package-name"
+    cabal "haddock" []
+
+    -- From the docs for `System.IO.openTempFile`:
+    --
+    --   On Windows, the template prefix may be truncated to 3 chars, e.g.
+    --   "foobar.ext" will be "fooXXX.ext".
+    let glob =
+          if isWindows
+            then "had*.txt"
+            else "haddock-response*.txt"
+
+    -- Check that there is a response file.
+    responseFiles <- assertGlobMatchesTestDir testTmpDir glob
+
+    -- Check that the matched response file is not empty, and is indeed a Haddock
+    -- response file.
+    assertAnyFileContains responseFiles "--package-name"

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

@@ -410,6 +410,10 @@ runTestM mode m =
                         -- effect on Windows.
                         , ("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)
+                        -- Windows uses `TMP` for the `TMPDIR`.
+                        , ("TMP", Just tmp_dir)
                         ],
                     testShouldFail = False,
                     testRelativeCurrentDir = ".",