From 519e7870b6b85262d3efc726f337bd0a4e8b8efa Mon Sep 17 00:00:00 2001
From: Eelco Dolstra <eelco.dolstra@logicblox.com>
Date: Thu, 19 Nov 2009 16:43:58 +0000
Subject: [PATCH] * Move `modifyDerivation' from build-support/vm to lib and
 rename it   to `overrideDerivation'.

svn path=/nixpkgs/trunk/; revision=18466
---
 pkgs/build-support/vm/default.nix | 13 ++--------
 pkgs/lib/attrsets.nix             |  2 +-
 pkgs/lib/customisation.nix        | 40 +++++++++++++++++++++++++++++++
 pkgs/lib/default.nix              |  2 ++
 4 files changed, 45 insertions(+), 12 deletions(-)
 create mode 100644 pkgs/lib/customisation.nix

diff --git a/pkgs/build-support/vm/default.nix b/pkgs/build-support/vm/default.nix
index 88ef284fa3b6..1a8e584d65f8 100644
--- a/pkgs/build-support/vm/default.nix
+++ b/pkgs/build-support/vm/default.nix
@@ -252,15 +252,6 @@ rec {
   '';
 
 
-  modifyDerivation = f: attrs:
-    let attrsCleaned = removeAttrs attrs ["meta" "passthru" "outPath" "drvPath"];
-        newDrv = derivation (attrsCleaned // (f attrs));
-    in newDrv //
-      { meta = if attrs ? meta then attrs.meta else {};
-        passthru = if attrs ? passthru then attrs.passthru else {};
-      };
-
-
   /* Run a derivation in a Linux virtual machine (using Qemu/KVM).  By
      default, there is no disk image; the root filesystem is a tmpfs,
      and /nix/store is shared with the host (via the CIFS protocol to
@@ -282,7 +273,7 @@ rec {
      `run-vm' will be left behind in the temporary build directory
      that allows you to boot into the VM and debug it interactively. */
      
-  runInLinuxVM = modifyDerivation (attrs: {
+  runInLinuxVM = drv: lib.overrideDerivation drv (attrs: {
     builder = "${bash}/bin/sh";
     args = ["-e" (vmRunCommand qemuCommandLinux)];
     origArgs = attrs.args;
@@ -317,7 +308,7 @@ rec {
      - Reboot to shutdown the machine (because Qemu doesn't seem
        capable of a APM/ACPI VM shutdown).
   */
-  runInGenericVM = modifyDerivation (attrs: {
+  runInGenericVM = drv: lib.overrideDerivation drv (attrs: {
     system = "i686-linux";
     builder = "${bash}/bin/sh";
     args = ["-e" (vmRunCommand qemuCommandGeneric)];
diff --git a/pkgs/lib/attrsets.nix b/pkgs/lib/attrsets.nix
index f6bf73a26fe6..729044586657 100644
--- a/pkgs/lib/attrsets.nix
+++ b/pkgs/lib/attrsets.nix
@@ -13,7 +13,7 @@ rec {
 
   /* Return an attribute from nested attribute sets.  For instance
      ["x" "y"] applied to some set e returns e.x.y, if it exists.  The
-     default value is returned otherwise.  */
+     default value is returned otherwise. */
   attrByPath = attrPath: default: e:
     let attr = head attrPath;
     in
diff --git a/pkgs/lib/customisation.nix b/pkgs/lib/customisation.nix
new file mode 100644
index 000000000000..889ce04547f2
--- /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 {};
+      };
+
+
+}
diff --git a/pkgs/lib/default.nix b/pkgs/lib/default.nix
index 2f916d3ddd73..3c760964a289 100644
--- a/pkgs/lib/default.nix
+++ b/pkgs/lib/default.nix
@@ -15,6 +15,7 @@ let
   misc = import ./misc.nix;
   maintainers = import ./maintainers.nix;
   platforms = import ./platforms.nix;
+  customisation = import ./customisation.nix;
 
 in
   { inherit trivial lists strings stringsWithDeps attrsets sources options
@@ -24,3 +25,4 @@ in
   # commonly used functions.
   // trivial // lists // strings // stringsWithDeps // attrsets // sources
   // properties // options // types // meta // debug // misc // modules
+  // customisation