Allow packages to be marked as "broken" by setting meta.broken

The effect is that they won't show up in "nix-env -qa" anymore.

doc/meta.xml

···
     package).</para></listitem>
   </varlistentry>
 
+  <varlistentry>
+    <term><varname>broken</varname></term>
+    <listitem><para>If set to <literal>true</literal>, the package is
+    marked as “broken”, meaning that it won’t show up in
+    <literal>nix-env -qa</literal>, and cannot be built or installed.
+    Sush packages should be removed from Nixpkgs eventually unless
+    they are fixed.</para></listitem>
+  </varlistentry>
+
 </variablelist>
 
 

nixos/modules/module-list.nix

···
   ./virtualisation/libvirtd.nix
   #./virtualisation/nova.nix
   ./virtualisation/virtualbox-guest.nix
-  ./virtualisation/xen-dom0.nix
+  #./virtualisation/xen-dom0.nix
 ]

pkgs/applications/virtualization/nova/client.nix

···
   meta = {
     homepage = https://github.com/rackspace/python-novaclient;
     description = "Client library and command line tool for the OpenStack Nova API";
+    broken = true;
   };
 }

pkgs/applications/virtualization/nova/default.nix

···
       paste_deploy m2crypto ipy boto_1_9 twisted sqlalchemy_migrate
       distutils_extra simplejson readline glance cheetah lockfile httplib2
       # !!! should libvirt be a build-time dependency?  Note that
-      # libxml2Python is a dependency of libvirt.py. 
+      # libxml2Python is a dependency of libvirt.py.
       libvirt libxml2Python
       novaclient
     ];
 
   buildInputs =
-    [ pythonPackages.python 
+    [ pythonPackages.python
       pythonPackages.wrapPython
       pythonPackages.mox
       intltool
···
       substituteInPlace nova/api/ec2/cloud.py \
         --replace 'sh genrootca.sh' $out/libexec/nova/genrootca.sh
     '';
-  
+
   buildPhase = "python setup.py build";
 
   installPhase =
-    ''    
+    ''
       p=$(toPythonPath $out)
       export PYTHONPATH=$p:$PYTHONPATH
       mkdir -p $p
···
       # computes some stuff from its own argv[0].  So put the wrapped
       # programs in $out/libexec under their original names.
       mkdir -p $out/libexec/nova
-      
+
       wrapProgram() {
           local prog="$1"
           local hidden=$out/libexec/nova/$(basename "$prog")
           mv $prog $hidden
           makeWrapper $hidden $prog "$@"
       }
-      
+
       wrapPythonPrograms
 
       cp -prvd etc $out/etc
···
   doCheck = false; # !!! fix
 
   checkPhase = "python setup.py test";
-    
+
   meta = {
     homepage = http://nova.openstack.org/;
     description = "OpenStack Compute (a.k.a. Nova), a cloud computing fabric controller";
+    broken = true;
   };
 }

pkgs/applications/virtualization/xen/default.nix

···
     description = "Xen hypervisor and management tools for Dom0";
     platforms = [ "i686-linux" "x86_64-linux" ];
     maintainers = [ stdenv.lib.maintainers.eelco ];
+    broken = true;
   };
 }

pkgs/stdenv/generic/default.nix

···
 
   allowUnfree = config.allowUnfree or true && builtins.getEnv "HYDRA_DISALLOW_UNFREE" != "1";
 
+  allowBroken = builtins.getEnv "NIXPKGS_ALLOW_BROKEN" == "1";
+
   stdenvGenerator = setupScript: rec {
 
     # The stdenv that we are producing.
···
         mkDerivation = attrs:
           if !allowUnfree && (let l = lib.lists.toList attrs.meta.license or []; in lib.lists.elem "unfree" l || lib.lists.elem "unfree-redistributable" l) then
             throw "package ‘${attrs.name}’ has an unfree license, refusing to evaluate"
+          else if !allowBroken && attrs.meta.broken or false then
+            throw "you can't use package ‘${attrs.name}’ because it has been marked as broken"
           else
             lib.addPassthru (derivation (
               (removeAttrs attrs ["meta" "passthru" "crossAttrs"])