[Git][ghc/ghc][wip/supersven/interpreter-flags] ghc: Distinguish between having an interpreter and having an internal one

26 Apr 2026


      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
=====================================
@@ -0,0 +1,17 @@
+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.



View it on GitLab: https://gitlab.haskell.org/ghc/ghc/-/commit/9efefc8c446eff2553330d563945b13c...

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Sven Tennie (＠supersven)

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