--keep-failed doesn't preserve build directory on failed multiple-outputs build.

[jcumming]

For example:

{ stdenv, fetchurl, libogg }:                                                                                                                                  

stdenv.mkDerivation rec {                                                                                                                                      
  name = "flac-1.2.1";                                                                                                                                         

  src = fetchurl {                                                                                                                                             
    url = mirror://sourceforge/flac/flac-1.2.1.tar.gz;                                                                                                         
    sha256 = "1pry5lgzfg57pga1zbazzdd55fkgk3v5qy4axvrbny5lrr5s8dcn";                                                                                           
  };                                                                                                                                                           

  buildInputs = [ libogg ];                                                                                                                                    

  patches =                                                                                                                                                    
    [ # Fix for building on GCC 4.3.                                                                                                                           
      (fetchurl {                                                                                                                                              
        url = "http://sources.gentoo.org/viewcvs.py/*checkout*/gentoo-x86/media-libs/flac/files/flac-1.2.1-gcc-4.3-includes.patch?rev=1.1";                    
        sha256 = "1m6ql5vyjb2jlp5qiqp6w0drq1m6x6y3i1dnl5ywywl3zd36k0mr";                                                                                       
      })                                                                                                                                                       
    ];                                                                                                                                                         

  enableParallelBuilding = true;                                                                                                                               

  outputs = [ "dev" "out" "bin" "doc" ];                                                                                                                       

  meta = {                                                                                                                                                     
    homepage = http://flac.sourceforge.net;                                                                                                                    
    description = "Library and tools for encoding and decoding the FLAC lossless audio file format";                                                           
  };                                                                                                                                                           
} 

If this is called with stdenv instead of stdenvMulti, it will fail to produce a bin output. This causes an assertion of the form:

builder for '/nix/store/iicb3pqgczqp9wwmjmx1xy3p0j5rsd8w-flac-1.2.1.drv' 
 failed to produce output path '/nix/store/bvb9sq100agrcxnimkcjjlc48any85hd-flac-1.2.1-bin'.` 

Unfortunately, --keep-failed doesn't keep the build directory around, making the source of the problem difficult to debug.

[shlevy]

This is more of an issue for https://github.com/NixOS/nix. Thanks for reporting though!

[jcumming]

Whoops! Is there an easy way to move it?

[shlevy]

Not that I know of, sorry.

[edolstra]

Fixed, thanks!