introduce importDir

avoid repeating myself

to create a new image, create a new folder under ./images that contains
a default.nix. That's it.

README.md

@@ -88,6 +88,15 @@ All images are automatically built and pushed to Docker Hub.
 | [nixpkgs/nix](https://hub.docker.com/r/nixpkgs/nix) | ![](https://images.microbadger.com/badges/image/nixpkgs/nix.svg) | ![](https://images.microbadger.com/badges/image/nixpkgs/nix:nixos-18.09.svg) |
 | [nixpkgs/nix-unstable](https://hub.docker.com/r/nixpkgs/nix-unstable) | ![](https://images.microbadger.com/badges/image/nixpkgs/nix-unstable.svg) | ![](https://images.microbadger.com/badges/image/nixpkgs/nix-unstable:nixos-18.09.svg) |
 
+## Adding new images
+
+To add a new image to the project, create a new folder under
+`./images/<image-name>` with a default.nix that returns the docker image.
+
+Then run `nix-build release.nix -A <image-name>` to test that it builds, and
+then use
+`docker load -i /nix/store/...<image-name>.tar.gz` to load and test the image.
+
 ## Related projects
 
 The [docker-library](https://github.com/docker-library/official-images#readme)

lib/importDir.nix

@@ -0,0 +1,21 @@
+{ lib }:
+
+importFn: baseDir:
+let
+  dirEntries =
+    builtins.attrNames
+      (lib.filterAttrs
+        (k: v: v == "directory")
+        (builtins.readDir baseDir));
+
+  absDirs =
+    builtins.map
+      (dir: "${toString baseDir}/${dir}")
+      dirEntries;
+
+  imports =
+    builtins.map
+      (dir: { name = builtins.baseNameOf dir; value = importFn dir; })
+      absDirs;
+in
+  builtins.listToAttrs imports

overlay.nix

@@ -1,18 +1,11 @@
-_: pkgs: {
-  # lib stuff can be in the top-level
+_: pkgs: let
+  importDir = import ./lib/importDir.nix {
+    inherit (pkgs) lib; 
+  };
+in {
+  # builder stuff can be in the top-level
   buildCLIImage = pkgs.callPackage ./lib/buildCLIImage.nix {};
 
   # docker images must be lower-cased
-  docker-nixpkgs = {
-
-    bash = pkgs.callPackage ./images/bash {};
-    busybox = pkgs.callPackage ./images/busybox {};
-    curl = pkgs.callPackage ./images/curl {};
-    docker-compose = pkgs.callPackage ./images/docker-compose {};
-    kubectl = pkgs.callPackage ./images/kubectl {};
-    kubernetes-helm = pkgs.callPackage ./images/kubernetes-helm {};
-    nix = pkgs.callPackage ./images/nix {};
-    nix-unstable = pkgs.callPackage ./images/nix-unstable {};
-
-  };
+  docker-nixpkgs = importDir (path: pkgs.callPackage path {}) ./images;
 }