concat: init

krebs/5pkgs/writers.nix

@@ -2,6 +2,32 @@
 with import <stockholm/lib>;
 {
   nixpkgs.config.packageOverrides = _: {
+
+    # Combine a list of derivations using symlinks.  Paths in later derivations
+    # take precedence over earlier ones.
+    #
+    # Example: create wrapper but retain all other files (man pages etc.)
+    #
+    # {
+    #   nixpkgs.config.packageOverrides = super: {
+    #     hello = pkgs.concat "hello" [
+    #       super.hello
+    #       (pkgs.writeDashBin "hello" ''
+    #         echo OMG
+    #         echo exec ${super.hello}/bin/hello "$@"
+    #       '')
+    #     ];
+    #   };
+    # }
+    #
+    concat = name: xs: pkgs.runCommand name {} ''
+      mkdir $out
+      ${flip concatMapStrings xs (x: ''
+        cp --remove-destination -vrs ${x}/* $out
+        find $out -type d -exec chmod -v u+rwx {} +
+      '')}
+    '';
+
     execve = name: { filename, argv ? null, envp ? {}, destination ? "" }: let
     in pkgs.writeC name { inherit destination; } /* c */ ''
       #include <unistd.h>