    {-# LANGUAGE CPP #-}

    module GHC.Exts.Heap.FFIClosures (module Reexport) where

    -- NOTE [hsc and CPP workaround]
    --
    -- # Problem
    --
    -- Often, .hsc files are used to get the correct offsets of C struct fields.
    -- Those structs may be affected by CPP directives e.g. profiled vs not profiled
    -- closure headers is affected by the PROFILED cpp define. Since we are building
    -- multiple variants of the RTS, we must support all possible offsets e.g. by
    -- running hsc2hs with cpp defines corresponding to each RTS flavour. The
    -- problem is that GHC's build system runs hsc2hs *only once* per .hsc file
    -- without properly setting cpp defines. This results in the same (probably
    -- incorrect) offsets into our C structs.
    --
    --
    -- # Workaround
    --
    -- To work around this issue, we create multiple .hsc files each manually
    -- defining thir cpp defines (see e.g. FFIClosures_ProfilingDisabled.hsc and
    -- FFIClosures_ProfilingEnabled.hsc). Then we rely on cpp defines working
    -- correctly in .hs files and use CPP to switch on which .hsc module to
    -- re-export (see below). In each case we import the desired .hsc module as
    -- `Reexport` and we import `()` (i.e. nothing) from all other .hsc variants
    -- just so that the build system sees all .hsc file as dependencies.
    --
    --
    -- # Future Work
    --
    -- - Duplication of the code in the .hsc files could be reduced simply by
    --   placing the code in a single .hsc.in file and `#include`ing it from each
    --   .hsc file. The .hsc files would only be responsible for setting the correct
    --   cpp defines. This currently doesn't work as hadrian doesn't know to copy
    --   the .hsc.in file to the build directory.
    -- - The correct solution would be for the build system to run `hsc2hs` with the
    --   correct cpp defines once per RTS flavour.
    --

    #if defined(PROFILING)
    import GHC.Exts.Heap.FFIClosures_ProfilingEnabled as Reexport
    import GHC.Exts.Heap.FFIClosures_ProfilingDisabled ()
      -- See Note [No way-dependent imports] in GHC.Exts.Heap.Closures

    #else
    import GHC.Exts.Heap.FFIClosures_ProfilingDisabled as Reexport
    import GHC.Exts.Heap.FFIClosures_ProfilingEnabled ()
      -- See Note [No way-dependent imports] in GHC.Exts.Heap.Closures

    #endif