Refine the GHCI macro into HAVE[_{INTERNAL, EXTERNAL}]_INTERPRETER

As discussed in #16331, the GHCI macro, defined through 'ghci' flags
in ghc.cabal.in, ghc-bin.cabal.in and ghci.cabal.in, is supposed to indicate
whether GHC is built with support for an internal interpreter, that runs in
the same process. It is however overloaded in a few places to mean
"there is an interpreter available", regardless of whether it's an internal
or external interpreter.

For the sake of clarity and with the hope of more easily being able to
build stage 1 GHCs with external interpreter support, this patch splits
the previous GHCI macro into 3 different ones:

- HAVE_INTERNAL_INTERPRETER: GHC is built with an internal interpreter
- HAVE_EXTERNAL_INTERPRETER: GHC is built with support for external interpreters
- HAVE_INTERPRETER: HAVE_INTERNAL_INTERPRETER || HAVE_EXTERNAL_INTERPRETER

3 files changed, 19 insertions, 8 deletions

diff --git a/libraries/ghci/GHCi/BreakArray.hs b/libraries/ghci/GHCi/BreakArray.hs
index 8d0e7495ba..41a2ab498f 100644
--- a/libraries/ghci/GHCi/BreakArray.hs
+++ b/libraries/ghci/GHCi/BreakArray.hs
@@ -19,7 +19,7 @@
 module GHCi.BreakArray
     (
       BreakArray
-#ifdef GHCI
+#if defined(HAVE_INTERPRETER)
           (BA) -- constructor is exported only for ByteCodeGen
     , newBreakArray
     , getBreak
@@ -29,7 +29,7 @@ module GHCi.BreakArray
 #endif
     ) where
 
-#ifdef GHCI
+#if defined(HAVE_INTERPRETER)
 import Prelude -- See note [Why do we import Prelude here?]
 import Control.Monad
 import Data.Word
diff --git a/libraries/ghci/GHCi/InfoTable.hsc b/libraries/ghci/GHCi/InfoTable.hsc
index 87d8f8f167..826e3bc2fd 100644
--- a/libraries/ghci/GHCi/InfoTable.hsc
+++ b/libraries/ghci/GHCi/InfoTable.hsc
@@ -10,13 +10,13 @@
 --
 module GHCi.InfoTable
   (
-#ifdef GHCI
+#if defined(HAVE_INTERPRETER)
     mkConInfoTable
 #endif
   ) where
 
 import Prelude -- See note [Why do we import Prelude here?]
-#ifdef GHCI
+#if defined(HAVE_INTERPRETER)
 import Foreign
 import Foreign.C
 import GHC.Ptr
@@ -27,13 +27,13 @@ import qualified Data.ByteString as BS
 #endif
 
 ghciTablesNextToCode :: Bool
-#ifdef TABLES_NEXT_TO_CODE
+#if defined(TABLES_NEXT_TO_CODE)
 ghciTablesNextToCode = True
 #else
 ghciTablesNextToCode = False
 #endif
 
-#ifdef GHCI /* To end */
+#if defined(HAVE_INTERPRETER) /* To end */
 -- NOTE: Must return a pointer acceptable for use in the header of a closure.
 -- If tables_next_to_code is enabled, then it must point the the 'code' field.
 -- Otherwise, it should point to the start of the StgInfoTable.
@@ -387,4 +387,4 @@ wORD_SIZE = (#const SIZEOF_HSINT)
 
 conInfoTableSizeB :: Int
 conInfoTableSizeB = wORD_SIZE + itblSize
-#endif /* GHCI */
+#endif /* HAVE_INTERPRETER */
diff --git a/libraries/ghci/ghci.cabal.in b/libraries/ghci/ghci.cabal.in
index 728927d3ce..f4c49137cc 100644
--- a/libraries/ghci/ghci.cabal.in
+++ b/libraries/ghci/ghci.cabal.in
@@ -22,6 +22,11 @@ Flag ghci
     Default: False
     Manual: True
 
+Flag ext-interp
+    Description: Build external interpreter support
+    Default: True
+    Manual: True
+
 source-repository head
     type:     git
     location: https://gitlab.haskell.org/ghc/ghc.git
@@ -48,7 +53,7 @@ library
         UnboxedTuples
 
     if flag(ghci)
-        CPP-Options: -DGHCI
+        CPP-Options: -DHAVE_INTERNAL_INTERPRETER
         exposed-modules:
             GHCi.Run
             GHCi.CreateBCO
@@ -56,6 +61,12 @@ library
             GHCi.Signals
             GHCi.TH
 
+    if flag(ext-interp)
+        CPP-Options: -DHAVE_EXTERNAL_INTERPRETER
+
+    if flag(ghci) || flag(ext-interp)
+        CPP-Options: -DHAVE_INTERPRETER
+
     include-dirs: @FFIIncludeDir@
 
     exposed-modules: