From 7f389f1d67f7cc9b0c634290dea8570f1f62c7d0 Mon Sep 17 00:00:00 2001
From: Moritz Angermann <moritz@stable-haskell.org>
Date: Fri, 5 Sep 2025 10:43:55 +0900
Subject: [PATCH] Conditionalize the ghc-internal dependency on the ghc
 version.

This change reverts part of !14544, which forces the bootstrap
compiler to have ghc-internal.  As such it breaks booting with
ghc 9.8.4. A better solution would be to make this conditional
on the ghc version in the cabal file!
---
 libraries/ghci/GHCi/CreateBCO.hs | 11 ++++++++++-
 libraries/ghci/GHCi/TH.hs        | 10 ++++++++++
 libraries/ghci/ghci.cabal.in     | 15 ++++++++++++++-
 3 files changed, 34 insertions(+), 2 deletions(-)

diff --git a/libraries/ghci/GHCi/CreateBCO.hs b/libraries/ghci/GHCi/CreateBCO.hs
index c1275a9b024e..847583e94969 100644
--- a/libraries/ghci/GHCi/CreateBCO.hs
+++ b/libraries/ghci/GHCi/CreateBCO.hs
@@ -6,6 +6,10 @@
 {-# LANGUAGE UnboxedTuples #-}
 {-# LANGUAGE RecordWildCards #-}
 {-# LANGUAGE CPP #-}
+-- Only needed when we don't have ghc-internal (and must import deprecated names)
+#ifndef HAVE_GHC_INTERNAL
+{-# OPTIONS_GHC -Wno-warnings-deprecations #-}
+#endif
 
 --
 --  (c) The University of Glasgow 2002-2006
@@ -26,8 +30,13 @@ import Data.Array.Base
 import Foreign hiding (newArray)
 import Unsafe.Coerce (unsafeCoerce)
 import GHC.Arr          ( Array(..) )
-import GHC.Exts   hiding ( BCO, mkApUpd0#, newBCO# )
+-- When ghc-internal is available prefer the non-deprecated exports.
+#ifdef HAVE_GHC_INTERNAL
+import GHC.Exts hiding ( BCO, mkApUpd0#, newBCO# )
 import GHC.Internal.Base ( BCO, mkApUpd0#, newBCO# )
+#else
+import GHC.Exts
+#endif
 import GHC.IO
 import Control.Exception ( ErrorCall(..) )
 
diff --git a/libraries/ghci/GHCi/TH.hs b/libraries/ghci/GHCi/TH.hs
index ace5382f7b6b..d409f4b5e971 100644
--- a/libraries/ghci/GHCi/TH.hs
+++ b/libraries/ghci/GHCi/TH.hs
@@ -1,6 +1,11 @@
 {-# LANGUAGE ScopedTypeVariables, StandaloneDeriving, DeriveGeneric,
     TupleSections, RecordWildCards, InstanceSigs, CPP #-}
 {-# OPTIONS_GHC -fno-warn-name-shadowing #-}
+-- Suppress deprecation warnings only when we must import deprecated symbols
+-- (i.e. when ghc-internal isn't available yet).
+#ifndef HAVE_GHC_INTERNAL
+{-# OPTIONS_GHC -Wno-warnings-deprecations #-}
+#endif
 
 -- |
 -- Running TH splices
@@ -109,7 +114,12 @@ import Data.IORef
 import Data.Map (Map)
 import qualified Data.Map as M
 import Data.Maybe
+-- Prefer the non-deprecated internal path when available.
+#ifdef HAVE_GHC_INTERNAL
 import GHC.Internal.Desugar (AnnotationWrapper(..))
+#else
+import GHC.Desugar (AnnotationWrapper(..))
+#endif
 import qualified GHC.Boot.TH.Syntax as TH
 import qualified GHC.Boot.TH.Monad as TH
 import Unsafe.Coerce
diff --git a/libraries/ghci/ghci.cabal.in b/libraries/ghci/ghci.cabal.in
index f64365545a3f..2daaeb50a5fc 100644
--- a/libraries/ghci/ghci.cabal.in
+++ b/libraries/ghci/ghci.cabal.in
@@ -86,7 +86,6 @@ library
         rts,
         array            == 0.5.*,
         base             >= 4.8 && < 4.23,
-        ghc-internal     >= 9.1001.0 && <=@ProjectVersionForLib@.0,
         ghc-prim         >= 0.5.0 && < 0.14,
         binary           == 0.8.*,
         bytestring       >= 0.10 && < 0.13,
@@ -97,6 +96,20 @@ library
         ghc-heap         >= 9.10.1 && <=@ProjectVersionMunged@,
         transformers     >= 0.5 && < 0.7
 
+    if impl(ghc > 9.10)
+        -- ghc-internal is only available (and required) when building
+        -- with a compiler that itself provides the ghc-internal
+        -- library.  Older bootstrap compilers (<= 9.10) don't ship it,
+        -- so we must not depend on it in that case.
+        --
+        -- When available we depend on the in-tree version (matching
+        -- @ProjectVersionForLib@) and define HAVE_GHC_INTERNAL so that
+        -- sources can import the non-deprecated modules from
+        -- GHC.Internal.* instead of the legacy (deprecated) locations.
+        Build-Depends:
+            ghc-internal      >= 9.1001.0 && <=@ProjectVersionForLib@.0
+        CPP-Options:          -DHAVE_GHC_INTERNAL
+
     if flag(bootstrap)
       build-depends:
             ghc-boot-th-next  == @ProjectVersionMunged@