GHC Panic on OS X: Data.Binary.Get.runGet: Invalid magic number "INPUT(-l"

When building the latest opencv-extra library on OS X I'm getting a GHC panic. To reproduce git clone https://github.com/LumiGuide/haskell-opencv, make sure Nix is installed and execute:

> nix-build -A haskellPackages.opencv-extra
...
[11 of 11] Compiling OpenCV.Extra     ( src/OpenCV/Extra.hs, dist/build/OpenCV/Extra.p_o )
ghc: panic! (the 'impossible' happened)
  (GHC version 8.6.3 for x86_64-apple-darwin):
        Data.Binary.Get.runGet at position 8: Invalid magic number "INPUT(-l"
CallStack (from HasCallStack):
  error, called at libraries/binary/src/Data/Binary/Get.hs:351:5 in binary-0.8.6.0:Data.Binary.Get

The library builds successfully on Linux.

Minimal test case: https://github.com/basvandijk/macos-ghc863-panic

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Upstream issue: https://gitlab.com/twittner/bytestring-conversion/issues/2

Looks like a darwin specific issue, perhaps even a nix on darwin specific issue. I can't reproduce this on NixOS.

I an reproduce this with nix on darwin though.

I was able to create a minimal test-case for this. Please have a look at:

https://github.com/basvandijk/macos-ghc863-panic

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As I just mentioned in the README I discovered that the panic is caused by a ghc -staticlib invocation. When I disable building a static library the build succeeds.

Corresponding NixOS issue #55848.

As I just discovered, apparently my libc++.a in my Nix store contains the following:

> cat /nix/store/jv40yw2ny28nnpbf860aaqq1dhga0f0r-libc++-5.0.2/lib/libc++.a
INPUT(-lc++_static -lc++abi)

Note that the first 8 bytes of this file are INPUT(- which is exactly what GHC is panicking about. It seems that GHC is expecting libc++.a to be a binary archive while in fact it's some kind of textual reference to the real archive libc++_static.a which can be found in the same directory.

Are these textual archive file a Nix-specific thing that GHC doesn't support?

Ok so on Nix libc++.a is an implicit linker script: INPUT(-lc++_static -lc++abi).

Maybe we should give GHC support for linker scripts. Initially it could just support the INPUT command.

This shouldn't be that hard. compiler/main/Ar.hs needs to be adapted.

Here's some work-in-progress on this:

https://github.com/basvandijk/ghc/commit/b2b92dde16275339293cedaa94d6745e69e904dc

I can confirm that this patch fixes this issue. Both macos-ghc863-panic, bytestring-conversion and opencv-extra build successfully with this patch and fail to build without it.

Next up is adding a test for this.

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ghc: panic! (the 'impossible' happened)
  (GHC version 8.6.5 for x86_64-apple-darwin):
        Data.Binary.Get.runGet at position 8: Invalid magic number "\202\254\186\190\NUL\NUL\NUL\STX"
CallStack (from HasCallStack):
  error, called at libraries/binary/src/Data/Binary/Get.hs:351:5 in binary-0.8.6.0:Data.Binary.Get

Please report this as a GHC bug:  http://www.haskell.org/ghc/reportabug

builder for '/nix/store/6jp8j06ig3c9wxiibn41yxll0nz0qpzq-hasktorch-0.2.0.0.drv' failed with exit code 1
cannot build derivation '/nix/store/8aqd29sqpdx9s6p2hbix7mqkvbwvk1c1-ghc-8.6.5-with-packages.drv': 1 dependencies couldn't be built

@trac-basvandijk Any update with this patch?

https://github.com/NixOS/nixpkgs/issues/55848#issuecomment-528495532

Apparently a different bug with almost the same error message.