driver: Introduce pgmcxx

Here we introduce proper support for compilation of C++ objects. This
includes:

 * logic in `configure` to detect the C++ toolchain and propagating this
   information into the `settings` file
 * logic in the driver to use the C++ toolchain when compiling C++
   sources

17 files changed, 55 insertions, 15 deletions

diff --git a/compiler/GHC/Driver/Session.hs b/compiler/GHC/Driver/Session.hs
index b78d141061..0af3549b7c 100644
--- a/compiler/GHC/Driver/Session.hs
+++ b/compiler/GHC/Driver/Session.hs
@@ -92,6 +92,7 @@ module GHC.Driver.Session (
         sPgm_P,
         sPgm_F,
         sPgm_c,
+        sPgm_cxx,
         sPgm_a,
         sPgm_l,
         sPgm_lm,
@@ -130,7 +131,7 @@ module GHC.Driver.Session (
         ghcUsagePath, ghciUsagePath, topDir,
         versionedAppDir, versionedFilePath,
         extraGccViaCFlags, globalPackageDatabasePath,
-        pgm_L, pgm_P, pgm_F, pgm_c, pgm_a, pgm_l, pgm_lm, pgm_dll, pgm_T,
+        pgm_L, pgm_P, pgm_F, pgm_c, pgm_cxx, pgm_a, pgm_l, pgm_lm, pgm_dll, pgm_T,
         pgm_windres, pgm_ar, pgm_otool, pgm_install_name_tool,
         pgm_ranlib, pgm_lo, pgm_lc, pgm_lcc, pgm_i,
         opt_L, opt_P, opt_F, opt_c, opt_cxx, opt_a, opt_l, opt_lm, opt_i,
@@ -823,6 +824,8 @@ pgm_F                 :: DynFlags -> String
 pgm_F dflags = toolSettings_pgm_F $ toolSettings dflags
 pgm_c                 :: DynFlags -> String
 pgm_c dflags = toolSettings_pgm_c $ toolSettings dflags
+pgm_cxx               :: DynFlags -> String
+pgm_cxx dflags = toolSettings_pgm_cxx $ toolSettings dflags
 pgm_a                 :: DynFlags -> (String,[Option])
 pgm_a dflags = toolSettings_pgm_a $ toolSettings dflags
 pgm_l                 :: DynFlags -> (String,[Option])
@@ -2163,6 +2166,8 @@ dynamic_flags_deps = [
       $ hasArg $ \f -> alterToolSettings $ \s -> s { toolSettings_pgm_F   = f }
   , make_ord_flag defFlag "pgmc"
       $ hasArg $ \f -> alterToolSettings $ \s -> s { toolSettings_pgm_c   = f }
+  , make_ord_flag defFlag "pgmcxx"
+      $ hasArg $ \f -> alterToolSettings $ \s -> s { toolSettings_pgm_cxx = f }
   , (Deprecated, defFlag  "pgmc-supports-no-pie"
       $ noArgM  $ \d -> do
         deprecate $ "use -pgml-supports-no-pie instead"
diff --git a/compiler/GHC/Settings.hs b/compiler/GHC/Settings.hs
index e6226696dc..5f1d97b01d 100644
--- a/compiler/GHC/Settings.hs
+++ b/compiler/GHC/Settings.hs
@@ -28,6 +28,7 @@ module GHC.Settings
   , sPgm_P
   , sPgm_F
   , sPgm_c
+  , sPgm_cxx
   , sPgm_a
   , sPgm_l
   , sPgm_lm
@@ -98,6 +99,7 @@ data ToolSettings = ToolSettings
   , toolSettings_pgm_P       :: (String, [Option])
   , toolSettings_pgm_F       :: String
   , toolSettings_pgm_c       :: String
+  , toolSettings_pgm_cxx     :: String
   , toolSettings_pgm_a       :: (String, [Option])
   , toolSettings_pgm_l       :: (String, [Option])
   , toolSettings_pgm_lm      :: Maybe (String, [Option])
@@ -208,6 +210,8 @@ sPgm_F :: Settings -> String
 sPgm_F = toolSettings_pgm_F . sToolSettings
 sPgm_c :: Settings -> String
 sPgm_c = toolSettings_pgm_c . sToolSettings
+sPgm_cxx :: Settings -> String
+sPgm_cxx = toolSettings_pgm_cxx . sToolSettings
 sPgm_a :: Settings -> (String, [Option])
 sPgm_a = toolSettings_pgm_a . sToolSettings
 sPgm_l :: Settings -> (String, [Option])
diff --git a/compiler/GHC/Settings/IO.hs b/compiler/GHC/Settings/IO.hs
index 308c5447e1..136607df27 100644
--- a/compiler/GHC/Settings/IO.hs
+++ b/compiler/GHC/Settings/IO.hs
@@ -78,6 +78,7 @@ initSettings top_dir = do
   targetPlatformString <- getSetting "target platform string"
   myExtraGccViaCFlags <- getSetting "GCC extra via C opts"
   cc_prog <- getToolSetting "C compiler command"
+  cxx_prog <- getToolSetting "C++ compiler command"
   cc_args_str <- getSetting "C compiler flags"
   cxx_args_str <- getSetting "C++ compiler flags"
   gccSupportsNoPie <- getBooleanSetting "C compiler supports -no-pie"
@@ -173,6 +174,7 @@ initSettings top_dir = do
       , toolSettings_pgm_P   = (cpp_prog, cpp_args)
       , toolSettings_pgm_F   = ""
       , toolSettings_pgm_c   = cc_prog
+      , toolSettings_pgm_cxx = cxx_prog
       , toolSettings_pgm_a   = (as_prog, as_args)
       , toolSettings_pgm_l   = (ld_prog, ld_args)
       , toolSettings_pgm_lm  = ld_r
diff --git a/compiler/GHC/SysTools/Tasks.hs b/compiler/GHC/SysTools/Tasks.hs
index 9b4400903e..ce741e2c1a 100644
--- a/compiler/GHC/SysTools/Tasks.hs
+++ b/compiler/GHC/SysTools/Tasks.hs
@@ -81,13 +81,13 @@ runPp logger dflags args = traceToolCommand logger "pp" $ do
 -- | Run compiler of C-like languages and raw objects (such as gcc or clang).
 runCc :: Maybe ForeignSrcLang -> Logger -> TmpFs -> DynFlags -> [Option] -> IO ()
 runCc mLanguage logger tmpfs dflags args = traceToolCommand logger "cc" $ do
-  let p = pgm_c dflags
-      args1 = map Option userOpts
+  let args1 = map Option userOpts
       args2 = languageOptions ++ args ++ args1
       -- We take care to pass -optc flags in args1 last to ensure that the
       -- user can override flags passed by GHC. See #14452.
   mb_env <- getGccEnv args2
-  runSomethingResponseFile logger tmpfs dflags cc_filter "C Compiler" p args2 mb_env
+  runSomethingResponseFile logger tmpfs dflags cc_filter dbgstring prog args2
+                           mb_env
  where
   -- discard some harmless warnings from gcc that we can't turn off
   cc_filter = unlines . doFilter . lines
@@ -143,17 +143,23 @@ runCc mLanguage logger tmpfs dflags args = traceToolCommand logger "cc" $ do
   -- compiling .hc files, by adding the -x c option.
   -- Also useful for plain .c files, just in case GHC saw a
   -- -x c option.
-  (languageOptions, userOpts) = case mLanguage of
-    Nothing -> ([], userOpts_c)
-    Just language -> ([Option "-x", Option languageName], opts)
+  (languageOptions, userOpts, prog, dbgstring) = case mLanguage of
+    Nothing -> ([], userOpts_c, pgm_c dflags, "C Compiler")
+    Just language -> ([Option "-x", Option languageName], opts, prog, dbgstr)
       where
-        (languageName, opts) = case language of
-          LangC      -> ("c",             userOpts_c)
-          LangCxx    -> ("c++",           userOpts_cxx)
-          LangObjc   -> ("objective-c",   userOpts_c)
-          LangObjcxx -> ("objective-c++", userOpts_cxx)
-          LangAsm    -> ("assembler",     [])
-          RawObject  -> ("c",             []) -- claim C for lack of a better idea
+        (languageName, opts, prog, dbgstr) = case language of
+          LangC      -> ("c",             userOpts_c
+                        ,pgm_c dflags,    "C Compiler")
+          LangCxx    -> ("c++",           userOpts_cxx
+                        ,pgm_cxx dflags , "C++ Compiler")
+          LangObjc   -> ("objective-c",   userOpts_c
+                        ,pgm_c dflags   , "Objective C Compiler")
+          LangObjcxx -> ("objective-c++", userOpts_cxx
+                        ,pgm_cxx dflags,  "Objective C++ Compiler")
+          LangAsm    -> ("assembler",     []
+                        ,pgm_c dflags,    "Asm Compiler")
+          RawObject  -> ("c",             []
+                        ,pgm_c dflags,    "C Compiler") -- claim C for lack of a better idea
   userOpts_c   = getOpts dflags opt_c
   userOpts_cxx = getOpts dflags opt_cxx
 
diff --git a/configure.ac b/configure.ac
index 6456721d2b..f9e64c3383 100644
--- a/configure.ac
+++ b/configure.ac
@@ -354,6 +354,7 @@ else
     # are screwed up. Configure doesn't think they're ever equal and
     # so never tried without the prefix.
     AC_PATH_PROG([CC],[gcc], [clang])
+    AC_PATH_PROG([CXX],[g++], [clang++])
     AC_PATH_PROG([NM],[nm])
     AC_PATH_PROG([LD],[ld])
     AC_PATH_PROG([AR],[ar])
@@ -472,6 +473,7 @@ AC_ARG_WITH([clang],
 dnl detect compiler (prefer gcc over clang) and set $CC (unless CC already set),
 dnl later CC is copied to CC_STAGE{1,2,3}
 AC_PROG_CC([cc gcc clang])
+AC_PROG_CXX([g++ clang++ c++])
 
 MAYBE_OVERRIDE_STAGE0([ar],[AR_STAGE0])
 
diff --git a/distrib/configure.ac.in b/distrib/configure.ac.in
index d5b99cbb8a..07e0687a9d 100644
--- a/distrib/configure.ac.in
+++ b/distrib/configure.ac.in
@@ -92,6 +92,7 @@ AC_ARG_ENABLE(distro-toolchain,
 dnl ** Which gcc to use?
 dnl --------------------------------------------------------------
 AC_PROG_CC([gcc clang])
+AC_PROG_CXX([g++ clang++ c++])
 
 dnl ** figure out how to invoke the C preprocessor (i.e. `gcc -E`)
 AC_PROG_CPP
diff --git a/docs/users_guide/phases.rst b/docs/users_guide/phases.rst
index 54ed63a06c..b784fa7662 100644
--- a/docs/users_guide/phases.rst
+++ b/docs/users_guide/phases.rst
@@ -38,6 +38,13 @@ given compilation phase:
 
     Use ⟨cmd⟩ as the C compiler.
 
+.. ghc-flag:: -pgmcxx ⟨cmd⟩
+    :shortdesc: Use ⟨cmd⟩ as the C++ compiler
+    :type: dynamic
+    :category: phase-programs
+
+    Use ⟨cmd⟩ as the C++ compiler.
+
 .. ghc-flag:: -pgmlo ⟨cmd⟩
     :shortdesc: Use ⟨cmd⟩ as the LLVM optimiser
     :type: dynamic
diff --git a/hadrian/bindist/Makefile b/hadrian/bindist/Makefile
index dbed7a0502..6b2e1f8754 100644
--- a/hadrian/bindist/Makefile
+++ b/hadrian/bindist/Makefile
@@ -105,6 +105,7 @@ lib/settings :
 	@echo '[("GCC extra via C opts", "$(GccExtraViaCOpts)")' >> $@
 	@echo ',("C compiler command", "$(SettingsCCompilerCommand)")' >> $@
 	@echo ',("C compiler flags", "$(SettingsCCompilerFlags)")' >> $@
+	@echo ',("C++ compiler command", "$(SettingsCxxCompilerCommand)")' >> $@
 	@echo ',("C++ compiler flags", "$(SettingsCxxCompilerFlags)")' >> $@
 	@echo ',("C compiler link flags", "$(SettingsCCompilerLinkFlags)")' >> $@
 	@echo ',("C compiler supports -no-pie", "$(SettingsCCompilerSupportsNoPie)")' >> $@
diff --git a/hadrian/cfg/system.config.in b/hadrian/cfg/system.config.in
index ae70823202..385279a435 100644
--- a/hadrian/cfg/system.config.in
+++ b/hadrian/cfg/system.config.in
@@ -142,6 +142,7 @@ ld-is-gnu-ld = @LdIsGNULd@
 ar-args = @ArArgs@
 
 settings-c-compiler-command = @SettingsCCompilerCommand@
+settings-cxx-compiler-command = @SettingsCxxCompilerCommand@
 settings-haskell-cpp-command = @SettingsHaskellCPPCommand@
 settings-haskell-cpp-flags = @SettingsHaskellCPPFlags@
 settings-c-compiler-flags = @SettingsCCompilerFlags@
diff --git a/hadrian/doc/user-settings.md b/hadrian/doc/user-settings.md
index 82f9964ac6..7b304ec0f3 100644
--- a/hadrian/doc/user-settings.md
+++ b/hadrian/doc/user-settings.md
@@ -369,6 +369,7 @@ the right names for them:
 	    argument for `hadrian/ghci` to work
 
   * `cc` refers to C compiler commands
+  * `cxx` refers to C++ compiler commands
 
     * `c.opts` for commands that call the C compiler on some C files
 	  * `deps.opts` for commands that call the C compiler for figuring out
diff --git a/hadrian/src/Oracles/Setting.hs b/hadrian/src/Oracles/Setting.hs
index 6ce01327c5..62a1ebcd67 100644
--- a/hadrian/src/Oracles/Setting.hs
+++ b/hadrian/src/Oracles/Setting.hs
@@ -106,6 +106,7 @@ data SettingList = ConfCcArgs Stage
 -- Eventually much of that local can probably be computed just in Hadrian.
 data SettingsFileSetting
     = SettingsFileSetting_CCompilerCommand
+    | SettingsFileSetting_CxxCompilerCommand
     | SettingsFileSetting_HaskellCPPCommand
     | SettingsFileSetting_HaskellCPPFlags
     | SettingsFileSetting_CCompilerFlags
@@ -198,6 +199,7 @@ settingList key = fmap words $ lookupSystemConfig $ case key of
 settingsFileSetting :: SettingsFileSetting -> Action String
 settingsFileSetting key = lookupSystemConfig $ case key of
     SettingsFileSetting_CCompilerCommand -> "settings-c-compiler-command"
+    SettingsFileSetting_CxxCompilerCommand -> "settings-cxx-compiler-command"
     SettingsFileSetting_HaskellCPPCommand -> "settings-haskell-cpp-command"
     SettingsFileSetting_HaskellCPPFlags -> "settings-haskell-cpp-flags"
     SettingsFileSetting_CCompilerFlags -> "settings-c-compiler-flags"
diff --git a/hadrian/src/Rules/Generate.hs b/hadrian/src/Rules/Generate.hs
index 5653bd1d25..1cd95d7961 100644
--- a/hadrian/src/Rules/Generate.hs
+++ b/hadrian/src/Rules/Generate.hs
@@ -298,6 +298,7 @@ generateSettings = do
         [ ("GCC extra via C opts", expr $ lookupSystemConfig "gcc-extra-via-c-opts")
         , ("C compiler command", expr $ settingsFileSetting SettingsFileSetting_CCompilerCommand)
         , ("C compiler flags", expr $ settingsFileSetting SettingsFileSetting_CCompilerFlags)
+        , ("C++ compiler command", expr $ settingsFileSetting SettingsFileSetting_CxxCompilerCommand)
         , ("C++ compiler flags", expr $ settingsFileSetting SettingsFileSetting_CxxCompilerFlags)
         , ("C compiler link flags", expr $ settingsFileSetting SettingsFileSetting_CCompilerLinkFlags)
         , ("C compiler supports -no-pie", expr $ settingsFileSetting SettingsFileSetting_CCompilerSupportsNoPie)
diff --git a/m4/fp_settings.m4 b/m4/fp_settings.m4
index dbacd3a816..0b75cf8d35 100644
--- a/m4/fp_settings.m4
+++ b/m4/fp_settings.m4
@@ -11,6 +11,7 @@ AC_DEFUN([FP_SETTINGS],
         mingw_bin_prefix='$$tooldir/mingw/bin/'
         SettingsCCompilerCommand="${mingw_bin_prefix}clang.exe"
         SettingsCCompilerFlags="$CONF_CC_OPTS_STAGE2"
+        SettingsCxxCompilerCommand="${mingw_bin_prefix}clang++.exe"
         SettingsCxxCompilerFlags="$CONF_CXX_OPTS_STAGE2"
         SettingsCCompilerLinkFlags="$CONF_GCC_LINKER_OPTS_STAGE2"
         SettingsHaskellCPPCommand="${mingw_bin_prefix}clang.exe"
@@ -32,6 +33,7 @@ AC_DEFUN([FP_SETTINGS],
 
         SettingsCCompilerCommand="$CC"
         SettingsCCompilerFlags="$CONF_CC_OPTS_STAGE2"
+        SettingsCxxCompilerCommand="$CXX"
         SettingsCxxCompilerFlags="$CONF_CXX_OPTS_STAGE2"
         SettingsHaskellCPPCommand="$HaskellCPPCmd"
         SettingsHaskellCPPFlags="$HaskellCPPArgs"
@@ -104,6 +106,7 @@ AC_DEFUN([FP_SETTINGS],
     SettingsCCompilerSupportsNoPie="$CONF_GCC_SUPPORTS_NO_PIE"
 
     AC_SUBST(SettingsCCompilerCommand)
+    AC_SUBST(SettingsCxxCompilerCommand)
     AC_SUBST(SettingsHaskellCPPCommand)
     AC_SUBST(SettingsHaskellCPPFlags)
     AC_SUBST(SettingsCCompilerFlags)
diff --git a/m4/fp_setup_windows_toolchain.m4 b/m4/fp_setup_windows_toolchain.m4
index 35e322c8a0..79a6ac6531 100644
--- a/m4/fp_setup_windows_toolchain.m4
+++ b/m4/fp_setup_windows_toolchain.m4
@@ -80,6 +80,7 @@ AC_DEFUN([FP_SETUP_WINDOWS_TOOLCHAIN],[
     mingwbin="$hardtop/inplace/mingw/bin/"
 
     CC="${mingwbin}clang.exe"
+    CXX="${mingwbin}clang++.exe"
     cflags="--rtlib=compiler-rt"
     CFLAGS="$cflags"
     CONF_CC_OPTS_STAGE1="$cflags"
diff --git a/mk/config.mk.in b/mk/config.mk.in
index 10ba35b79b..fdbaab58b9 100644
--- a/mk/config.mk.in
+++ b/mk/config.mk.in
@@ -358,7 +358,7 @@ BIN_DIST_TAR_COMP       = $(BIN_DIST_NAME)-$(TARGETPLATFORM).tar.$(TAR_COMP_EXT)
 # SRC_HC_OPTS is *not* for adding flags that are required to make your
 # build work.  Examples:
 #
-#  - instead of using -pgmc/-pgma-/-pgml, use the --with-gcc option to configure
+#  - instead of using -pgmc/-pgmcxx/-pgma-/-pgml, use the --with-gcc option to configure
 #
 #  - if you need -optc, -opta, or -optl flags, the CONF_CC_* and CONF_LD_*
 #    variables are more appropriate (set via configure)
@@ -457,6 +457,7 @@ TargetHasLibm = @TargetHasLibm@
 TablesNextToCode = @TablesNextToCode@
 
 SettingsCCompilerCommand = @SettingsCCompilerCommand@
+SettingsCxxCompilerCommand = @SettingsCxxCompilerCommand@
 SettingsHaskellCPPCommand = @SettingsHaskellCPPCommand@
 SettingsHaskellCPPFlags = @SettingsHaskellCPPFlags@
 SettingsCCompilerFlags = @SettingsCCompilerFlags@
diff --git a/rts/include/ghc.mk b/rts/include/ghc.mk
index b8b74f4a89..92a70538d1 100644
--- a/rts/include/ghc.mk
+++ b/rts/include/ghc.mk
@@ -193,6 +193,7 @@ $(includes_SETTINGS) : rts/include/Makefile | $$(dir $$@)/.
 	@echo '[("GCC extra via C opts", "$(GccExtraViaCOpts)")' >> $@
 	@echo ',("C compiler command", "$(SettingsCCompilerCommand)")' >> $@
 	@echo ',("C compiler flags", "$(SettingsCCompilerFlags)")' >> $@
+	@echo ',("C++ compiler command", "$(SettingsCxxCompilerCommand)")' >> $@
 	@echo ',("C++ compiler flags", "$(SettingsCxxCompilerFlags)")' >> $@
 	@echo ',("C compiler link flags", "$(SettingsCCompilerLinkFlags)")' >> $@
 	@echo ',("C compiler supports -no-pie", "$(SettingsCCompilerSupportsNoPie)")' >> $@
diff --git a/testsuite/ghc-config/ghc-config.hs b/testsuite/ghc-config/ghc-config.hs
index efb88f81f2..b38401b433 100644
--- a/testsuite/ghc-config/ghc-config.hs
+++ b/testsuite/ghc-config/ghc-config.hs
@@ -35,6 +35,7 @@ main = do
   getGhcFieldProgWithDefault fields "LLC" "LLVM llc command" "llc"
   getGhcFieldProgWithDefault fields "TEST_CC" "C compiler command" "gcc"
   getGhcFieldProgWithDefault fields "TEST_CC_OPTS" "C compiler flags" ""
+  getGhcFieldProgWithDefault fields "TEST_CXX" "C++ compiler command" "g++"
 
 getGhcFieldOrFail :: [(String,String)] -> String -> String -> IO ()
 getGhcFieldOrFail fields mkvar key