Add stubs for FFI functions

Without these stubs HLS wouldn't be able to provide completion in any
module that directly or indirectly includes any of the
'Data.Array.Accelerate.Pattern.*' modules.

haskell/haskell-language-server#365

src/Data/Array/Accelerate/Debug/Internal/Flags.hs

@@ -161,6 +161,12 @@ clearFlags = mapM_ clearFlag
 -- notEnabled = error $ unlines [ "Data.Array.Accelerate: Debugging options are disabled."
 --                              , "Reinstall package 'accelerate' with '-fdebug' to enable them." ]
 
+-- FIXME: HLS requires stubs because it does not process the
+--        'addForeignFilePath' calls when evaluating Template Haskell
+--
+--        https://github.com/haskell/haskell-language-server/issues/365
+#ifndef __GHCIDE__
+
 -- Import the underlying flag variables. These are defined in the file
 -- cbits/flags.h as a bitfield and initialised at program initialisation.
 --
@@ -174,6 +180,19 @@ foreign import ccall "&__cmd_line_flags" __cmd_line_flags :: Ptr Word32
 foreign import ccall "&__unfolding_use_threshold"   unfolding_use_threshold   :: Value  -- the magic cut-off figure for inlining
 foreign import ccall "&__max_simplifier_iterations" max_simplifier_iterations :: Value  -- maximum number of scalar simplification passes
 
+#else
+
+__cmd_line_flags :: Ptr Word32
+__cmd_line_flags = undefined
+
+unfolding_use_threshold   :: Value
+unfolding_use_threshold = undefined
+
+max_simplifier_iterations :: Value
+max_simplifier_iterations = undefined
+
+#endif
+
 -- These @-f<blah>@ flags can be reversed with @-fno-<blah>@
 --
 seq_sharing           = Flag  0 -- recover sharing of sequence expressions

src/Data/Atomic.hs

@@ -1,3 +1,4 @@
+{-# LANGUAGE CPP #-}
 {-# LANGUAGE ForeignFunctionInterface #-}
 {-# LANGUAGE MagicHash                #-}
 {-# LANGUAGE NoImplicitPrelude        #-}
@@ -49,6 +50,12 @@ newtype Atomic = Atomic ( Ptr Int64 )
 --   write a v
 --   return a
 
+-- FIXME: HLS requires stubs because it does not process the
+--        'addForeignFilePath' calls when evaluating Template Haskell
+--
+--        https://github.com/haskell/haskell-language-server/issues/365
+#ifndef __GHCIDE__
+
 -- | Get the current value.
 --
 foreign import ccall unsafe "atomic_read_64" read :: Atomic -> IO Int64
@@ -69,6 +76,25 @@ foreign import ccall unsafe "atomic_fetch_and_and_64" and :: Atomic -> Int64 ->
 --
 foreign import ccall unsafe "atomic_fetch_and_sub_64" subtract :: Atomic -> Int64 -> IO Int64
 
+#else
+
+read :: Atomic -> IO Int64
+read = undefined
+
+write :: Atomic -> Int64 -> IO ()
+write = undefined
+
+add :: Atomic -> Int64 -> IO Int64
+add = undefined
+
+and :: Atomic -> Int64 -> IO Int64
+and = undefined
+
+subtract :: Atomic -> Int64 -> IO Int64
+subtract = undefined
+
+#endif
+
 -- SEE: [linking to .c files]
 --
 runQ $ do