hadrian: Don't depend upon bash from PATH

Previously Hadrian depended implicitly upon whatever `bash` it found in
`PATH`, offerring no way for the user to override. Fix this by detecting
`sh` in `configure` and passing the result to Hadrian.

Fixes #19797.

configure.ac

@@ -255,6 +255,8 @@ AC_CANONICAL_TARGET
 
 FPTOOLS_SET_PLATFORM_VARS
 
+FP_PROG_SH
+
 # Verify that the installed (bootstrap) GHC is capable of generating
 # code for the requested build platform.
 if test "$BuildPlatform" != "$bootstrap_target"

hadrian/cfg/system.config.in

@@ -28,6 +28,7 @@ patch          = @PatchCmd@
 xelatex        = @XELATEX@
 makeindex      = @MAKEINDEX@
 makeinfo       = @MAKEINFO@
+bourne-shell   = @SH@
 
 # Python 3 is required to run test driver.
 # See: https://github.com/ghc/ghc/blob/master/testsuite/mk/boilerplate.mk#L220

hadrian/src/Builder.hs

@@ -27,6 +27,7 @@ import Hadrian.Builder.Tar
 import Hadrian.Oracles.Path
 import Hadrian.Oracles.TextFile
 import Hadrian.Utilities
+import Oracles.Setting (bashPath)
 import System.Exit
 import System.IO (stderr)
 
@@ -254,7 +255,9 @@ instance H.Builder Builder where
 
                 Ar Unpack _ -> cmd' echo [Cwd output] [path] buildArgs
 
-                Autoreconf dir -> cmd' echo [Cwd dir] ["sh", path] buildArgs
+                Autoreconf dir -> do
+                  bash <- bashPath
+                  cmd' echo [Cwd dir] [bash, path] buildArgs
 
                 Configure  dir -> do
                     -- Inject /bin/bash into `libtool`, instead of /bin/sh,

hadrian/src/Hadrian/Oracles/Path.hs

 {-# LANGUAGE TypeFamilies #-}
 module Hadrian.Oracles.Path (
-    lookupInPath, bashPath, fixAbsolutePathOnWindows, pathOracle
+    lookupInPath, fixAbsolutePathOnWindows, pathOracle
     ) where
 
 import Control.Monad
@@ -20,10 +20,6 @@ lookupInPath name
     | name == takeFileName name = askOracle $ LookupInPath name
     | otherwise                 = return name
 
--- | Lookup the path to the @bash@ interpreter.
-bashPath :: Action FilePath
-bashPath = lookupInPath "bash"
-
 -- | Fix an absolute path on Windows:
 -- * "/c/" => "C:/"
 -- * "/usr/bin/tar.exe" => "C:/msys/usr/bin/tar.exe"

hadrian/src/Oracles/Setting.hs

@@ -7,7 +7,7 @@ module Oracles.Setting (
 
     -- * Helpers
     ghcCanonVersion, cmdLineLengthLimit, hostSupportsRPaths, topDirectory,
-    libsuf, ghcVersionStage,
+    libsuf, ghcVersionStage, bashPath,
 
     -- ** Target platform things
     anyTargetPlatform, anyTargetOs, anyTargetArch, anyHostOs,
@@ -76,6 +76,7 @@ data Setting = BuildArch
              | TargetArchHaskell
              | TargetOsHaskell
              | TargetArmVersion
+             | BourneShell
 
 -- TODO: Reduce the variety of similar flags (e.g. CPP and non-CPP versions).
 -- | Each 'SettingList' comes from the file @hadrian/cfg/system.config@,
@@ -172,6 +173,7 @@ setting key = lookupValueOrError configFile $ case key of
     TargetVendor       -> "target-vendor"
     TargetArchHaskell  -> "target-arch-haskell"
     TargetOsHaskell    -> "target-os-haskell"
+    BourneShell        -> "bourne-shell"
 
 -- | Look up the value of a 'SettingList' in @cfg/system.config@, tracking the
 -- result.
@@ -217,6 +219,10 @@ settingsFileSetting key = lookupValueOrError configFile $ case key of
 getSetting :: Setting -> Expr c b String
 getSetting = expr . setting
 
+-- | The path to a Bourne shell interpreter.
+bashPath :: Action FilePath
+bashPath = setting BourneShell
+
 -- | An expression that looks up the value of a 'SettingList' in
 -- @cfg/system.config@, tracking the result.
 getSettingList :: SettingList -> Args c b

m4/fp_prog_sh.m4

+# FP_PROG_SH
+# ------------
+# Find a functional Bourne shell
+AC_DEFUN([FP_PROG_SH],
+[
+ AC_REQUIRE([FPTOOLS_SET_PLATFORM_VARS]) dnl for $windows
+ AC_ARG_VAR(SH,[Use as the full path to a Bourne shell. [default=autodetect]])
+ AC_PATH_PROGS([SH], [sh bash])
+ if test "$windows" = "YES"; then
+   dnl use mixed (-m) mode to get C:/mingw64/... with forward slashes.
+   dnl     windows (-w) mode will give us C:\... and mess with escaping.
+   SH=`cygpath -m "$SH"`
+ fi
+ AC_SUBST([SH])[]dnl
+])# FP_PROG_SH