This was first reported on the Stack issue tracker at https://github.com/commercialhaskell/stack/issues/1161, but I've traced it to the fact that GHC uses shell script wrappers for many common commands, including ghc, ghci, and hsc2hs.

Background: Mac OS X 10.11 introduced System Integrity Protection, which treats parts of the filesystem specially to prevent tampering with the system. Among those protections is that executables in /bin, such as /bin/sh, have the DYLD_LIBRARY_PATH variable stripped from the environment before being invoked.

Since ghc, hsc2hs, and others are shell scripts that use #!/bin/sh, it means DYLD_LIBRARY_PATH is stripped from the environment when invoking them. I was able to work around this issue by copying /bin/sh to my home directory and then modifying the #! path in the hsc2hs to use the copy.

I'm not sure what the best way to move forward is. Some possibilities I can think of:

• Have installer tools for OS X (such as Stack, ghcformacosx, and Homebrew) apply the workaround themselves, although that leaves out anyone who installs directly from an official bindist or builds from source, and is a duplication of effort.
• Have make install on OS X copy /bin/sh and "fix" the wrappers itself.
• Replace the shell script wrappers with something written in Haskell that reads the paths from a configuration file.

Note: I set the component to hsc2hs since that's where I encountered the problem, but I wouldn't be surprised if it also effected other cases (like ghci, and ghc with Template Haskell). I also hesitated to categorize this a "bug" since it's OS X's weird behaviour, and not actually something I feel GHC is doing wrong, causing this problem. But I doubt OS X is going to change, although it is possible (but not recommended) to disable SIP by booting into recovery mode and running csrutil disable, after which these protections are no longer in place.