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Sven Tennie pushed to branch wip/supersven/interpreter-flags at Glasgow Haskell Compiler / GHC

Commits:

9efefc8c

by Sven Tennie at 2026-04-26T13:11:24+02:00

ghc: Distinguish between having an interpreter and having an internal one

Actually, these are related but different things:

- ghc can run an interpreter (either internal or external)
- ghc is compiled with an internal interpreter

Splitting the logic solves compiler warnings and expresses the intent
better.

6 changed files:

+ changelog.d/T19174.md
ghc/GHC/Driver/Session/Mode.hs
ghc/GHCi/UI.hs
ghc/Main.hs
ghc/ghc-bin.cabal.in
hadrian/src/Settings/Packages.hs

Changes:

changelog.d/T19174.md

 +section: compiler
 +issues: #19174
 +mrs: !15714
 +synopsis:
 +  Introduce HAVE_INTERPRETER flag separate from HAVE_INTERNAL_INTERPRETER
 +description:
 +  GHC now distinguishes between having any interpreter support (internal or
 +  external) via the `HAVE_INTERPRETER` CPP flag, and having specifically
 +  an internal interpreter via `HAVE_INTERNAL_INTERPRETER`. The `ghc-bin`
 +  package now has separate `interpreter` and `internal-interpreter` cabal
 +  flags. Interactive mode and GHCi UI features now check `HAVE_INTERPRETER`
 +  instead of `HAVE_INTERNAL_INTERPRETER`, while internal interpreter-specific
 +  code (like the directory change handler in GHCi) remains guarded by
 +  `HAVE_INTERNAL_INTERPRETER`. In cross-compilation builds, the
 +  `internal-interpreter` flag is disabled while the `interpreter` flag can
 +  still be enabled for external interpreter support.
 +  This does not change current behaviour, but prevents compiler warnings.

ghc/GHC/Driver/Session/Mode.hs

@@ -132,7 +132,7 @@ isDoEvalMode :: Mode -> Bool
  isDoEvalMode (Right (Right (DoEval _))) = True
  isDoEvalMode _ = False
 -#if defined(HAVE_INTERNAL_INTERPRETER)
 +#if defined(HAVE_INTERPRETER)
  isInteractiveMode :: PostLoadMode -> Bool
  isInteractiveMode DoInteractive = True
  isInteractiveMode _             = False

ghc/GHCi/UI.hs

@@ -1909,7 +1909,9 @@ changeDirectory dir = do
        fhv <- compileGHCiExpr $
          "System.Directory.setCurrentDirectory " ++ show dir'
        liftIO $ evalIO interp fhv
 +#if defined(HAVE_INTERNAL_INTERPRETER)
      _ -> pure ()
 +#endif
  trySuccess :: GhciMonad m => m SuccessFlag -> m SuccessFlag
  trySuccess act =

ghc/Main.hs

@@ -36,7 +36,7 @@ import GHC.Driver.Config.Diagnostic
  import GHC.Platform
  import GHC.Platform.Host
 -#if defined(HAVE_INTERNAL_INTERPRETER)
 +#if defined(HAVE_INTERPRETER)
  import GHCi.UI              ( interactiveUI, ghciWelcomeMsg, defaultGhciSettings, languageEditionMsg )
  #endif
@@ -288,7 +288,7 @@ doRun units srcs args = do
      args' = drop 1 $ dropWhile (/= "--") $ map unLoc args
  ghciUI :: [String] -> [(FilePath, Maybe Phase)] -> Maybe [String] -> Ghc ()
 -#if !defined(HAVE_INTERNAL_INTERPRETER)
 +#if !defined(HAVE_INTERPRETER)
  ghciUI _ _ _ =
    throwGhcException (CmdLineError "not built for interactive use")
  #else
@@ -332,7 +332,7 @@ showBanner :: PostLoadMode -> DynFlags -> IO ()
  showBanner _postLoadMode dflags = do
     let verb = verbosity dflags
 -#if defined(HAVE_INTERNAL_INTERPRETER)
 +#if defined(HAVE_INTERPRETER)
     -- Show the GHCi banner
     when (isInteractiveMode _postLoadMode && verb >= 1) $
      do putStrLn ghciWelcomeMsg

ghc/ghc-bin.cabal.in

@@ -22,6 +22,11 @@ Flag internal-interpreter
      Default: False
      Manual: True
 +Flag interpreter
 +    Description: Build with interpreter support, both internal and external.
 +    Default: False
 +    Manual: True
++
  Flag threaded
      Description: Link the ghc executable against the threaded RTS
      Default: True
@@ -56,7 +61,7 @@ Executable ghc
                   -rtsopts=all
                   "-with-rtsopts=-K512M -H -I5 -T"
 -    if flag(internal-interpreter)
 +    if flag(interpreter)
          -- NB: this is never built by the bootstrapping GHC+libraries
          Build-depends:
              deepseq        >= 1.4 && < 1.6,
@@ -65,7 +70,7 @@ Executable ghc
              haskeline      == 0.8.*,
              exceptions     == 0.10.*,
              time           >= 1.8 && < 1.16
 -        CPP-Options: -DHAVE_INTERNAL_INTERPRETER
 +        CPP-Options: -DHAVE_INTERPRETER
          Other-Modules:
              GHCi.Leak
              GHCi.UI
@@ -82,6 +87,9 @@ Executable ghc
              UnboxedTuples
              ViewPatterns
 +    if flag(internal-interpreter)
 +       CPP-Options: -DHAVE_INTERNAL_INTERPRETER
++
      if flag(threaded)
        ghc-options: -threaded

hadrian/src/Settings/Packages.hs

@@ -114,7 +114,8 @@ packageArgs = do
               , compilerStageOption ghcDebugAssertions ? arg "-DDEBUG" ]
            , builder (Cabal Flags) ? mconcat
 -            [ (expr (ghcWithInterpreter stage)) `cabalFlag` "internal-interpreter"
 +            [ expr (ghcWithInterpreter stage) `cabalFlag` "interpreter"
 +            , andM [expr (ghcWithInterpreter stage), notCross] `cabalFlag` "internal-interpreter"
              , ifM stage0
                    -- We build a threaded stage 1 if the bootstrapping compiler
                    -- supports it.