1 files changed, 46 insertions, 0 deletions
diff --git a/pkgs/lib/composable-derivation.nix b/pkgs/lib/composable-derivation.nix
new file mode 100644
index 0000000000000..790a0bcc9dbcb
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+++ b/pkgs/lib/composable-derivation.nix
@@ -0,0 +1,46 @@
+{lib, pkgs} :
+let inherit (lib) nv nvs; in
+{
+  # see new python derivations for example..
+  # You should be able to override anything you like easily
+  # grep the mailinglist by title "python proposal" (dec 08)
+  # -> http://mail.cs.uu.nl/pipermail/nix-dev/2008-December/001571.html
+  # to see why this got complicated when using all its features
+  composableDerivation = {
+          # modify args before applying stdenv.mkDerivation, this should remove at least attrs removeAttrsBy
+        f ? lib.prepareDerivationArgs,
+        stdenv ? pkgs.stdenv,
+          # initial set of arguments to be passed to stdenv.mkDerivation passing prepareDerivationArgs by default
+        initial ? {},
+          # example func :  (x: x // { x.buildInputs ++ ["foo"] }), but see mergeAttrByFunc which does this for you
+        merge ? (lib.mergeOrApply lib.mergeAttrByFunc)
+      }: lib.applyAndFun
+            (args: stdenv.mkDerivation (f args))
+            merge
+            (merge { inherit (lib) mergeAttrBy; } initial);
+
+  # some utility functions
+  # use this function to generate flag attrs for prepareDerivationArgs
+  # E nable  D isable F eature
+  edf = {name, feat ? name, enable ? {}, disable ? {} , value ? ""}:
+    nvs name {
+    set = {
+      configureFlags = ["--enable-${feat}${if value == "" then "" else "="}${value}"];
+    } // enable;
+    unset = {
+      configureFlags = ["--disable-${feat}"];
+    } // disable;
+  };
+
+  # same for --with and --without-
+  # W ith or W ithout F eature
+  wwf = {name, feat ? name, enable ? {}, disable ? {}, value ? ""}:
+    nvs name {
+    set = {
+      configureFlags = ["--with-${feat}${if value == "" then "" else "="}${value}"];
+    } // enable;
+    unset = {
+      configureFlags = ["--without-${feat}"];
+    } // disable;
+  };
+}