crash when evaluating module

[teto]

I am trying to write some module that generates a (neo)vim config based on buildInputs (will create a proper python3Env etc). The crash happens when running this nix-shell : https://github.com/teto/mptcpanalyzer/blob/fda8ffb12976c3de31f537386b02eb9ded09ca9d/contrib/shell.nix with this nixpkgs (nixos-unstable plus my WIP patches): https://github.com/teto/nixpkgs/commit/a3b1357549b620d3d9b6d290d34d9615099a89ab

When I try to test it, nix crashes: nix (Nix) 2.2

I fear the backtrace might not be very helpful as is but I don't hae yet a good workflow on nixpkgs for gdb (any hint/tip appreciated):

           PID: 19542 (nix-shell)
           UID: 1000 (teto)
           GID: 100 (users)
        Signal: 11 (SEGV)
     Timestamp: Mon 2019-03-11 15:37:34 JST (37s ago)
  Command Line: nix-shell
    Executable: /nix/store/08i4l3pxx0z7ndrbbcwnbr2nxml6gh0r-nix-2.2/bin/nix
 Control Group: /user.slice/user-1000.slice/session-1.scope
          Unit: session-1.scope
         Slice: user-1000.slice
       Session: 1
     Owner UID: 1000 (teto)
       Boot ID: 92207d172c3340d8a0f746b739a091ee
    Machine ID: 1aa845d7be064cb893633636b9b393d7
      Hostname: jedha
       Storage: /var/lib/systemd/coredump/core.nix-shell.1000.92207d172c3340d8a0f746b739a091ee.19542.1552286254000000.lz4 (truncated)
       Message: Process 19542 (nix-shell) of user 1000 dumped core.

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Reading symbols from /nix/store/08i4l3pxx0z7ndrbbcwnbr2nxml6gh0r-nix-2.2/bin/nix...(no debugging symbols found)...done.
BFD: warning: /var/tmp/coredump-F9asqf is truncated: expected core file size >= 4248256512, found: 2147483648

warning: core file may not match specified executable file.

warning: platform-specific solib_create_inferior_hook did not load initial shared libraries.
Cannot access memory at address 0x7f7eb36a40e8
Cannot access memory at address 0x7f7eb36a40e0
Failed to read a valid object file image from memory.
Core was generated by `nix-shell'.
Program terminated with signal SIGSEGV, Segmentation fault.
#0  0x0000000000436b38 in boost::io::basic_altstringbuf<char, std::char_traits<char>, std::allocator<char> >::overflow(int) ()
[Current thread is 1 (LWP 19542)]
+(gdb) bt
#0  0x0000000000436b38 in boost::io::basic_altstringbuf<char, std::char_traits<char>, std::allocator<char> >::overflow(int) ()
Backtrace stopped: Cannot access memory at address 0x7fff9beb59a8