Allow marking licenses as unfree

This allows licenses like the Amazon Software License to be identified
properly while still preventing packages with those licenses from
being distributed in the Nixpkgs/NixOS channels.

lib/licenses.nix

@@ -25,6 +25,7 @@ rec {
     shortName = "asl";
     fullName = "Amazon Software License";
     url = http://aws.amazon.com/asl/;
+    free = false;
   };
 
   amd = {
@@ -290,11 +291,21 @@ rec {
     url = http://www.tcl.tk/software/tcltk/license.html;
   };
 
-  unfree = "unfree";
+  unfree = {
+    fullName = "Unfree";
+    free = false;
+  };
 
-  unfreeRedistributable = "unfree-redistributable";
+  unfreeRedistributable = {
+    fullName = "Unfree redistributable";
+    free = false;
+  };
 
-  unfreeRedistributableFirmware = "unfree-redistributable-firmware";
+  unfreeRedistributableFirmware = {
+    fullName = "Unfree redistributable firmware";
+    # Note: we currently consider these "free" for inclusion in the
+    # channel and NixOS images.
+  };
 
   unlicense = {
     shortName = "Unlicense";

pkgs/stdenv/generic/default.nix

@@ -41,6 +41,9 @@ let
 
   unsafeGetAttrPos = builtins.unsafeGetAttrPos or (n: as: null);
 
+  isUnfree = licenses: lib.lists.any (l:
+    !l.free or true || l == "unfree" || l == "unfree-redistributable") licenses;
+
   # The stdenv that we are producing.
   result =
 
@@ -84,7 +87,7 @@ let
               unsafeGetAttrPos "name" attrs;
           pos' = if pos != null then "‘" + pos.file + ":" + toString pos.line + "’" else "«unknown-file»";
         in
-        if !allowUnfree && (let l = lib.lists.toList attrs.meta.license or []; in lib.lists.elem "unfree" l || lib.lists.elem "unfree-redistributable" l) && !(allowUnfreePredicate attrs) then
+        if !allowUnfree && isUnfree (lib.lists.toList attrs.meta.license or []) && !allowUnfreePredicate attrs then
           throw ''
             Package ‘${attrs.name}’ in ${pos'} has an unfree license, refusing to evaluate.
             ${forceEvalHelp "Unfree"}''