Fixup #9614: make config file extraction from help text more robust (#9667)

* Fixup #9614: make config file extraction from help text more robust

The previous test (PR #9614) did not work when the config file was
absent, because then the help text would add one more line at the
end (see issue #535).

The new test looks for the exact line printed before the line with the
config file.

We test both scenarios, with config file present or absent.

* Trim lines before searching the marker to work around CRLF issues.

---------

Co-authored-by: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>

Author: andreasabel

cabal-install/src/Distribution/Client/Main.hs

@@ -397,6 +397,10 @@ mainWorker args = do
       pname <- getProgName
       configFile <- defaultConfigFile
       putStr (help pname)
+      -- Andreas Abel, 2024-01-28: https://github.com/haskell/cabal/pull/9614
+      -- See cabal-testsuite/PackageTests/Help/HelpPrintsConfigFile/
+      -- Third-party tools may rely on the specific wording
+      -- to find the config file in the help text, so do not change!
       putStr $
         "\nYou can edit the cabal configuration file to set defaults:\n"
           ++ "  "

cabal-testsuite/PackageTests/Help/HelpPrintsConfigFile/help-prints-config-file.out

@@ -1 +1,2 @@
 # cabal --help
+# cabal --help

cabal-testsuite/PackageTests/Help/HelpPrintsConfigFile/help-prints-config-file.test.hs

@@ -1,25 +1,52 @@
--- Andreas Abel, 2024-01-13
+-- Andreas Abel, 2024-01-13, 2024-01-28
 --
--- Ensure that the last line of the help text is the name of the config file.
+-- Ensure that the help text prints the name of the config file, following a fixed text.
 -- This invariant is used by clients such as the Haskell setup github action.
 -- See: https://github.com/haskell-actions/setup/pull/63
 
+-- The end of the help text should look like:
+--
+-- > You can edit the cabal configuration file to set defaults:
+-- >   <<HOME>>/.cabal/config
+-- > This file will be generated with sensible defaults if you run 'cabal update'.
+--
+-- The last line is only present when the file does *not* exist.
+--
+-- So while usually the last line is the name of the config file,
+-- the correct way is to take the line after the fixed text "You can edit...".
+
 import Distribution.Utils.String (trim)
+import System.Directory (removeFile)
 import Test.Cabal.Prelude
 
 main = cabalTest $ do
   env <- getTestEnv
-  res <- cabal' "--help" []
+  let configFile = testUserCabalConfigFile env
 
-  -- The end of the help text should be something like:
-  --
-  -- > You can edit the cabal configuration file to set defaults:
-  -- >   <<HOME>>/.cabal/config
-  --
-  -- So trimming the last line will give us the name of the config file.
-  let configFile = trim . last . lines . resultOutput $ res
+  -- Test 1: with config file present.
+  test configFile "Case: config file exists."
 
-  -- Verify that this is indeed the config file.
-  assertEqual "Last line of help text should be name of the config file"
-    (testUserCabalConfigFile env)
+  -- Test 2: with config file absent.
+  liftIO $ removeFile configFile
+  test configFile "Case: config file does not exist."
+
+test configFile info = do
+  res <- cabal' "--help" []
+  assertEqual (unwords ["Help text contains name of the config file after the marker.", info])
     configFile
+    (configFileFromHelpText $ resultOutput res)
+
+-- | The config file is the line following the fixed text:
+--   "You can edit the cabal configuration file to set defaults:"
+--
+--   If this marker is not found, return the empty string.
+configFileFromHelpText :: String -> FilePath
+configFileFromHelpText txt =
+    case found of
+      _marker : l : _ -> l
+      _ -> ""
+  where
+    marker = "You can edit the cabal configuration file to set defaults:"
+    (_before, found) = break (marker ==) $ map trim $ lines txt
+       -- Note: 'trim' lines to get rid of CR on Windows;
+       -- 'lines' does not seem to remove it.

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

@@ -330,7 +330,7 @@ runTestM mode m = withSystemTempDirectory "cabal-testsuite" $ \tmp_dir -> do
                         -- Set CABAL_DIR in addition to HOME, since HOME has no
                         -- effect on Windows.
                         , ("CABAL_DIR", Just (testCabalDir env))
-                        , ("CABAL_CONFIG", Just $ testCabalDir env </> "config")
+                        , ("CABAL_CONFIG", Just (testUserCabalConfigFile env))
                         ],
                     testShouldFail = False,
                     testRelativeCurrentDir = ".",