Fix --host= triple mangling during cross-compilation

Cabal/src/Distribution/Simple.hs

@@ -135,6 +135,7 @@ import Language.Haskell.Extension
 
 -- Base
 import Data.List (unionBy, (\\))
+import qualified Data.Map as Map
 import System.Directory (removePathForcibly)
 import System.Environment (getArgs, getProgName)
 import System.IO (hPutStr, hPutStrLn)
@@ -981,12 +982,14 @@ autoconfUserHooks =
         let common = configCommonFlags flags
             verbosity = mkVerbosity defaultVerbosityHandles (fromFlag $ setupVerbosity common)
             mbWorkDir = flagToMaybe $ setupWorkingDir common
+            compilerTargetTriple = Map.lookup "Target platform" (compilerProperties (compiler lbi))
         runConfigureScript
           defaultVerbosityHandles
           flags
           (flagAssignment lbi)
           (withPrograms lbi)
           (hostPlatform lbi)
+          compilerTargetTriple
         pbi <- getHookedBuildInfo verbosity mbWorkDir (buildDir lbi)
         sanityCheckHookedBuildInfo verbosity pkg_descr pbi
         let pkg_descr' = updatePackageDescription pbi pkg_descr
@@ -1055,9 +1058,12 @@ autoconfSetupHooks =
               { LBC.configFlags = cfg
               , LBC.flagAssignment = flags
               , LBC.hostPlatform = plat
+              , LBC.compiler = compiler'
               }
           }
-        ) = runConfigureScript defaultVerbosityHandles cfg flags progs plat
+        ) =
+        let compilerTargetTriple = Map.lookup "Target platform" (compilerProperties compiler')
+         in runConfigureScript defaultVerbosityHandles cfg flags progs plat compilerTargetTriple
 
     pre_conf_comp
       :: SetupHooks.PreConfComponentInputs

Cabal/src/Distribution/Simple/ConfigureScript.hs

@@ -23,7 +23,6 @@ import Prelude ()
 
 -- local
 import Distribution.PackageDescription
-import Distribution.Pretty
 import Distribution.Simple.Configure (findDistPrefOrDefault)
 import Distribution.Simple.Errors
 import Distribution.Simple.LocalBuildInfo
@@ -56,8 +55,18 @@ runConfigureScript
   -> ProgramDb
   -> Platform
   -- ^ host platform
+  -> Maybe String
+  -- ^ The GHC target platform triple (e.g. @"x86_64-w64-mingw32"@),
+  -- passed as the autoconf @--host=@ flag.
+  --
+  -- Note: GHC's \"target\" is the platform that compiled Haskell code
+  -- runs on, which corresponds to autoconf's \"host\" (the platform
+  -- where the compiled artifact runs). Autoconf reserves \"target\"
+  -- for compiler toolchains only. See the
+  -- [GHC wiki on cross-compilation](https://gitlab.haskell.org/ghc/ghc/-/wikis/cross-compilation)
+  -- for details on GHC's platform terminology.
   -> IO ()
-runConfigureScript verbHandles cfg flags programDb hp = do
+runConfigureScript verbHandles cfg flags programDb hp targetTriple = do
   let commonCfg = configCommonFlags cfg
       verbosity = mkVerbosity verbHandles (fromFlag $ setupVerbosity commonCfg)
   dist_dir <- findDistPrefOrDefault $ setupDistPref commonCfg
@@ -183,7 +192,15 @@ runConfigureScript verbHandles cfg flags programDb hp = do
           : [("CXXFLAGS", Just (mkFlagsEnv cxxFlags "CXXFLAGS")) | Just cxxFlags <- [mcxxFlags]]
           ++ [("PATH", Just pathEnv) | not (null extraPath)]
           ++ cabalFlagEnv
-      maybeHostFlag = ["--host=" ++ show (pretty hp) | hp /= buildPlatform]
+      maybeHostFlag =
+        case targetTriple of
+          Just host ->
+            [ "--host=" ++ host
+            | -- the hp =/ buildPlatform guard is too restrictive,
+            -- e.g. for glibc -> musl cross-compilation we don't want to omit x86_64-unknown-linux-musl.
+            hp /= buildPlatform
+            ]
+          Nothing -> []
       args' =
         configureFile'
           : args

cabal-testsuite/PackageTests/ConfigureHostTriple/A.hs

@@ -0,0 +1 @@
+module A where

cabal-testsuite/PackageTests/ConfigureHostTriple/Setup.hs

@@ -0,0 +1,6 @@
+module Main (main) where
+
+import Distribution.Simple
+
+main :: IO ()
+main = defaultMainWithHooks autoconfUserHooks

cabal-testsuite/PackageTests/ConfigureHostTriple/configure

@@ -0,0 +1,4 @@
+#!/bin/sh
+# Minimal configure script that records its arguments.
+# We write all args to configure-args.txt so the test can inspect them.
+echo "$@" > configure-args.txt

cabal-testsuite/PackageTests/ConfigureHostTriple/scripts/fake-ghc.sh

@@ -0,0 +1,14 @@
+#!/bin/sh
+
+# A fake GHC that proxies the real GHC but overrides
+# "Target platform" to simulate cross-compilation
+# to x86_64-w64-mingw32.
+
+case "$*" in
+    *--info*)
+        ghc "$@" | sed 's/("Target platform","[^"]*")/("Target platform","x86_64-w64-mingw32")/'
+        ;;
+    *)
+        exec ghc "$@"
+        ;;
+esac

cabal-testsuite/PackageTests/ConfigureHostTriple/setup.test.hs

@@ -0,0 +1,42 @@
+import Test.Cabal.Prelude
+import Test.Cabal.Script (runghc)
+import Control.Monad.IO.Class
+import Data.List (isInfixOf)
+
+-- When cross-compiling, Cabal passes a --host= flag to configure scripts.
+-- The value should be the original GNU triple (e.g. x86_64-w64-mingw32),
+-- not Cabal's canonical platform string (e.g. x86_64-windows).
+--
+-- This test uses a fake GHC wrapper that reports "x86_64-w64-mingw32"
+-- as its Target platform (simulating a cross-compiler), then checks
+-- that the configure script receives --host=x86_64-w64-mingw32
+-- rather than the mangled --host=x86_64-windows.
+main = do
+    skipIfWindows "uses sh script as fake ghc"
+    setupTest $ recordMode DoNotRecord $ do
+        env <- getTestEnv
+        let cwd = testCurrentDir env
+            fakeGhc = cwd </> "scripts" </> "fake-ghc.sh"
+        -- Run Setup.hs configure with our fake cross-compiler.
+        -- We call runghc ourselves to bypass the test framework's
+        -- --with-ghc which would override ours.
+        _ <- liftIO $ runghc
+            (testScriptEnv env)
+            (Just $ testTmpDir env)
+            (testEnvironment env)
+            ("." </> "Setup.hs")
+            [ "configure"
+            , "--distdir", testDistDir env
+            , "--with-compiler", fakeGhc
+            ]
+        -- The configure script writes its arguments to configure-args.txt
+        -- in its working directory (dist/build/).
+        let argsFile = testDistDir env </> "build" </> "configure-args.txt"
+        args <- liftIO $ readFile argsFile
+        -- The configure script should receive --host=x86_64-w64-mingw32
+        -- (the original GNU triple), not --host=x86_64-windows.
+        unless ("--host=x86_64-w64-mingw32" `isInfixOf` args) $
+            error $ unlines
+                [ "Expected --host=x86_64-w64-mingw32 in configure arguments"
+                , "but got: " ++ args
+                ]

cabal-testsuite/PackageTests/ConfigureHostTriple/test.cabal

@@ -0,0 +1,9 @@
+cabal-version: 2.2
+name: test
+version: 0
+build-type: Configure
+
+library
+  exposed-modules: A
+  build-depends: base
+  default-language: Haskell2010

changelog.d/pr-11718.md

@@ -0,0 +1,15 @@
+---
+synopsis: Fix --host= triple mangling during cross-compilation
+packages: [cabal-install]
+prs: 11718
+issues: 5887
+---
+
+repairs (hopefully): https://github.com/haskell/cabal/issues/5887
+
+Cabal now passes the unchanged GHC target platform triple as the autoconf --host, instead of a simplified version.
+
+For example, Cabal now passes the full `--host=x86_64-w64-mingw32` instead of the incorrect `--host=x86_64-windows`.
+
+Adds an integration test which fails on master
+and now succeeds.