GHCi.FFI: ignore ffi.h and friends for js-backend

1 files changed, 35 insertions, 4 deletions

diff --git a/libraries/ghci/GHCi/FFI.hsc b/libraries/ghci/GHCi/FFI.hsc
index 74c9e175b1..64cb962325 100644
--- a/libraries/ghci/GHCi/FFI.hsc
+++ b/libraries/ghci/GHCi/FFI.hsc
@@ -6,7 +6,24 @@
 --
 -----------------------------------------------------------------------------
 
+{- Note [FFI for the JS-Backend]
+   ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+
+   The JS-backend does not use GHC's native rts, as such you might think that it
+   doesn't require ghci. However, that is not true, because we need ghci in
+   order to interoperate with iserv even if we do not use any of the FFI stuff
+   in this file. So obviously we do not require libffi, but we still need to be
+   able to build ghci in order for the JS-Backend to supply its own iserv
+   interop solution. Thus we bite the bullet and wrap all the unneeded bits in a
+   CPP conditional compilation blocks that detect the JS-backend. A necessary
+   evil to be sure; notice that the only symbols remaining the JS_HOST_ARCH case
+   are those that are explicitly exported by this module and set to error if
+   they are every used.
+-}
+
+#if !defined(js_HOST_ARCH)
 #include <ffi.h>
+#endif
 
 {-# LANGUAGE CPP, DeriveGeneric, DeriveAnyClass #-}
 module GHCi.FFI
@@ -18,11 +35,13 @@ module GHCi.FFI
   ) where
 
 import Prelude -- See note [Why do we import Prelude here?]
+#if !defined(js_HOST_ARCH)
 import Control.Exception
+import Foreign.C
+#endif
 import Data.Binary
 import GHC.Generics
 import Foreign
-import Foreign.C
 
 data FFIType
   = FFIVoid
@@ -51,6 +70,7 @@ prepForeignCall
     -> FFIType            -- result type
     -> IO (Ptr C_ffi_cif) -- token for making calls (must be freed by caller)
 
+#if !defined(js_HOST_ARCH)
 prepForeignCall cconv arg_types result_type = do
   let n_args = length arg_types
   arg_arr <- mallocArray n_args
@@ -66,12 +86,25 @@ prepForeignCall cconv arg_types result_type = do
         " res ty: ", show result_type, ")" ]
   else
     return (castPtr cif)
+#else
+prepForeignCall _ _ _ =
+  error "GHCi.FFI.prepForeignCall: Called with JS_HOST_ARCH! Perhaps you need to run configure?"
+#endif
+
 
 freeForeignCallInfo :: Ptr C_ffi_cif -> IO ()
 freeForeignCallInfo p = do
+#if !defined(js_HOST_ARCH)
   free ((#ptr ffi_cif, arg_types) p)
   free p
+#else
+  error "GHCi.FFI.freeForeignCallInfo: Called with JS_HOST_ARCH! Perhaps you need to run configure?"
+#endif
 
+data C_ffi_type
+data C_ffi_cif
+
+#if !defined(js_HOST_ARCH)
 strError :: C_ffi_status -> String
 strError r
   | r == fFI_BAD_ABI
@@ -103,9 +136,6 @@ ffiType FFIUInt16   = ffi_type_uint16
 ffiType FFIUInt32   = ffi_type_uint32
 ffiType FFIUInt64   = ffi_type_uint64
 
-data C_ffi_type
-data C_ffi_cif
-
 type C_ffi_status = (#type ffi_status)
 type C_ffi_abi    = (#type ffi_abi)
 
@@ -161,3 +191,4 @@ foreign import ccall "ffi_prep_cif"
 --            -> Ptr ()                    -- put result here
 --            -> Ptr (Ptr ())              -- arg values
 --            -> IO ()
+#endif