* Move `modifyDerivation' from build-support/vm to lib and rename it

  to `overrideDerivation'.

svn path=/nixpkgs/trunk/; revision=18466

1 files changed, 40 insertions, 0 deletions

diff --git a/pkgs/lib/customisation.nix b/pkgs/lib/customisation.nix
new file mode 100644
index 00000000000..889ce04547f
--- /dev/null
+++ b/pkgs/lib/customisation.nix
@@ -0,0 +1,40 @@
+{
+
+
+  /* `overrideDerivation drv f' takes a derivation (i.e., the result
+     of a call to the builtin function `derivation') and returns a new
+     derivation in which the attributes of the original are overriden
+     according to the function `f'.  This function is called with the
+     original derivation attributes.
+
+     `overrideDerivation' allows certain "ad-hoc" customisation
+     scenarios (e.g. in ~/.nixpkgs/config.nix).  For instance, if you
+     want to "patch" the derivation returned by a package function in
+     Nixpkgs to build another version than what the function itself
+     provides, you can do something like this:
+
+       mySed = overrideDerivation pkgs.gnused (oldAttrs: {
+         name = "sed-4.2.2-pre";
+         src = fetchurl {
+           url = ftp://alpha.gnu.org/gnu/sed/sed-4.2.2-pre.tar.bz2;
+           sha256 = "11nq06d131y4wmf3drm0yk502d2xc6n5qy82cg88rb9nqd2lj41k";
+         };
+         patches = [];
+       });
+
+     For another application, see build-support/vm, where this
+     function is used to build arbitrary derivations inside a QEMU
+     virtual machine. */
+     
+  overrideDerivation = drv: f:
+    let
+      # Filter out special attributes.
+      attrs = removeAttrs drv ["meta" "passthru" "outPath" "drvPath"];
+      newDrv = derivation (attrs // (f drv));
+    in newDrv //
+      { meta = if drv ? meta then drv.meta else {};
+        passthru = if drv ? passthru then drv.passthru else {};
+      };
+
+
+}