Fix #8645: no assertion warning on special modes (help, version, etc.) (#8647)

* Fix #8654: no assertion warning on special modes (help, version, etc.)

This patch moves the `warnIfAssertionsAreEnabled` until after the main
command line argument parsing, and then only prints it on regular
operation, i.e. not when just the help or version of cabal was
demanded, or the command line could not be parsed.

Further, the warning is printed on stderr.  The previous attempt to
use `warn` does not work as expected, as the verbosity aperatshnik
isn't in place yet, so the warning cannot be suppressed by -v0.

Drive-by-shooting: straighten the convoluted control flow involving
`maybeScriptAndArgs`.  This IO computation was invoked "brutto"
before, when it is actually only needed in *one* branch of the case
distinction.

* PR #8647: changelog, fix text of warning

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

Author: andreasabel

cabal-install/main/Main.hs

@@ -1,4 +1,6 @@
-{-# LANGUAGE CPP, ScopedTypeVariables #-}
+{-# LANGUAGE CPP #-}
+{-# LANGUAGE LambdaCase #-}
+{-# LANGUAGE ScopedTypeVariables #-}
 
 -----------------------------------------------------------------------------
 -- |
@@ -149,7 +151,7 @@ import Distribution.Simple.Program.Db (reconfigurePrograms)
 import qualified Distribution.Simple.Setup as Cabal
 import Distribution.Simple.Utils
          ( cabalVersion, die', dieNoVerbosity, info, notice, topHandler
-         , findPackageDesc, tryFindPackageDesc, createDirectoryIfMissingVerbose, warn )
+         , findPackageDesc, tryFindPackageDesc, createDirectoryIfMissingVerbose )
 import Distribution.Text
          ( display )
 import Distribution.Verbosity as Verbosity
@@ -162,7 +164,7 @@ import System.Environment       (getArgs, getProgName)
 import System.FilePath          ( dropExtension, splitExtension
                                 , takeExtension, (</>), (<.>) )
 import System.IO                ( BufferMode(LineBuffering), hSetBuffering
-                                , stderr, stdout )
+                                , hPutStrLn, stderr, stdout )
 import System.Directory         ( doesFileExist, getCurrentDirectory
                                 , withCurrentDirectory)
 import Data.Monoid              (Any(..))
@@ -178,9 +180,6 @@ main = do
   -- This is especially important for CI and build systems.
   hSetBuffering stdout LineBuffering
 
-  -- Check whether assertions are enabled and print a warning in that case.
-  warnIfAssertionsAreEnabled
-
   -- If the locale encoding for CLI doesn't support all Unicode characters,
   -- printing to it may fail unless we relax the handling of encoding errors
   -- when writing to stderr and stdout.
@@ -189,20 +188,20 @@ main = do
   (args0, args1) <- break (== "--") <$> getArgs
   mainWorker =<< (++ args1) <$> expandResponse args0
 
+-- | Check whether assertions are enabled and print a warning in that case.
 warnIfAssertionsAreEnabled :: IO ()
 warnIfAssertionsAreEnabled =
   assert False (return ()) `catch`
-  (\(_e :: AssertionFailed) -> warn normal assertionsEnabledMsg)
+  (\(_e :: AssertionFailed) -> hPutStrLn stderr assertionsEnabledMsg)
+    -- Andreas, 2022-12-30, issue #8654:
+    -- The verbosity machinery is not in place at this point (option -v not parsed),
+    -- so instead of using function @warn@, we print straight to stderr.
   where
     assertionsEnabledMsg =
-      "this is a debug build of cabal-install with assertions enabled."
+      "Warning: this is a debug build of cabal-install with assertions enabled."
 
 mainWorker :: [String] -> IO ()
 mainWorker args = do
-  maybeScriptAndArgs <- case args of
-    []     -> return Nothing
-    (h:tl) -> (\b -> if b then Just (h:|tl) else Nothing) <$> CmdRun.validScript h
-
   topHandler $
     case commandsRun (globalCommand commands) commands args of
       CommandHelp   help                 -> printGlobalHelp help
@@ -216,9 +215,22 @@ mainWorker args = do
               -> printNumericVersion
           CommandHelp     help           -> printCommandHelp help
           CommandList     opts           -> printOptionsList opts
-          CommandErrors   errs           -> maybe (printErrors errs) go maybeScriptAndArgs where
-            go (script:|scriptArgs) = CmdRun.handleShebang script scriptArgs
-          CommandReadyToGo action        -> action globalFlags
+
+          CommandErrors   errs           -> do
+            -- Check whether cabal is called from a script, like #!/path/to/cabal.
+            case args of
+              []      -> printErrors errs
+              script : scriptArgs -> CmdRun.validScript script >>= \case
+                False -> printErrors errs
+                True  -> do
+                  -- In main operation (not help, version etc.) print warning if assertions are on.
+                  warnIfAssertionsAreEnabled
+                  CmdRun.handleShebang script scriptArgs
+
+          CommandReadyToGo action        -> do
+            -- In main operation (not help, version etc.) print warning if assertions are on.
+            warnIfAssertionsAreEnabled
+            action globalFlags
 
   where
     printCommandHelp help = do

changelog.d/pr-8647

@@ -0,0 +1,13 @@
+synopsis: No up-front warning that assertions are on for special commands (help, version, numeric-version)
+packages: cabal-install
+prs: #8647
+issues: #8645
+
+description: {
+
+- When compiled with ghc option `-fno-ignore-assert`, `cabal-install` will issue a generic warning that assertions are on.
+  This warning will no longer be emitted for special modes of operation like `cabal --numeric-version`, `--version` and help,
+  and also not if `cabal` could not parse its command line.
+  Further, the warning now goes to `stderr` rather than `stdout`.
+
+}