Implementing a fix allowing deepOverride without changing dependency-tree-leaf packages

svn path=/nixpkgs/trunk/; revision=22533

1 files changed, 5 insertions, 0 deletions

diff --git a/pkgs/lib/attrsets.nix b/pkgs/lib/attrsets.nix
index c1903368291..f39b46db621 100644
--- a/pkgs/lib/attrsets.nix
+++ b/pkgs/lib/attrsets.nix
@@ -270,4 +270,9 @@ rec {
       else eqStrict pat val
     ) [pattern attrs]));
 
+  # override only the attributes that are already present in the old set
+  # useful for deep-overriding
+  overrideExisting = old: new:
+  old // listToAttrs (map (attr: nameValuePair attr (attrByPath [attr] (getAttr attr old) new)) (attrNames old));
+
 }