Fails to build in a nix derivation

[harendra-kumar]

nix-develop fails with this error;

       > [3 of 3] Linking dist/build/FileSystem.Event.Darwin/FileSystem.Event.Darwin
       > Undefined symbols for architecture x86_64:
       >   "_FSEventStreamEventFlagItemCloned", referenced from:
       >       _streamlyzmfseventszm0zi1zi0zm3vXYsi9XG6MJY5kSD8JwQW_StreamlyziInternalziFSziEventziDarwin_isClonedzumask_info in libHSstreamly-fsevents-0.1.0-3vXYsi9XG6MJY5kSD8JwQW.a(Darwin.o)
       > ld: symbol(s) not found for architecture x86_64
       > clang-16: error: linker command failed with exit code 1 (use -v to see invocation)
       > ghc-9.6.6: `cc' failed in phase `Linker'. (Exit code: 1)
       > <<ghc: 78659072 bytes, 1 GCs, 5266776/5266776 avg/max bytes residency (1 samples), 804M in use, 0.016 INIT (0.016 elapsed), 0.237 MUT (3.934 elapsed), 0.010 GC (0.012 elapsed) :ghc>>
       For full logs, run:
         nix-store -l /nix/store/6l2br46v48lkchgnqfscp0hxzwmg958j-streamly-fsevents-0.1.0.drv
error: 1 dependencies of derivation '/nix/store/hr4ja4hi1xny3nqcs17ic1kp6ggzhhmq-ghc-9.6.6-with-packages.drv' failed to build

When using nix-develop what happens is:

1. The SDK is newer (10.15.6 in the log).
2. The deployment target is older (10.12.0).
3. Clang says: “Yes, this symbol exists, but it’s guarded by availability macros.” → configure interprets that as “symbol exists,” so it sets HAVE_DECL_KFSEVENTSTREAMEVENTFLAGITEMCLONED=1.
4. Later, when the code tries to actually use it, the linker fails (because the symbol isn’t exposed at runtime for 10.12).

So configure wrongly sets HAVE_DECL_KFSEVENTSTREAMEVENTFLAGITEMCLONED=1.

In nix-shell somehow the SDK pulled is 10.12 and the deployment target is also 10.12 - therefore, it build correctly.

src/Streamly/Internal/FS/Event/Darwin.c

#include <CoreServices/CoreServices.h>

#if __MAC_OS_X_VERSION_MIN_REQUIRED >= 101300
UInt32 FSEventStreamEventFlagItemCloned () {
  return kFSEventStreamEventFlagItemCloned;
}
#endif

src/Streamly/Internal/FS/Event/Darwin.hs

{-# LANGUAGE CPP #-}

module Streamly.Internal.FS.Event.Darwin
    ( isCloned
    ) where

import Data.Word (Word32)

#if HAVE_DECL_KFSEVENTSTREAMEVENTFLAGITEMCLONED
foreign import ccall safe
    "FSEventStreamEventFlagItemCloned"
    kFSEventStreamEventFlagItemCloned :: Word32

-- | Determine whether the event indicates cloning of an object within the
-- monitored path. The "Duplicate" command in the "File" menu of the "Finder"
-- application generates a "clone" event.
--
-- Applicable only when 'setFileEvents' is 'True'.
--
-- /macOS 10.13+/
--
-- /Pre-release/
--
isCloned :: Event -> Bool
isCloned = getFlag kFSEventStreamEventFlagItemCloned
#endif