From 6c4a69fa4280f0154ce257a1dfd23fb463c1ec5b Mon Sep 17 00:00:00 2001
From: Vincent Ambo <tazjin@google.com>
Date: Wed, 25 Aug 2021 13:53:31 +0300
Subject: [PATCH] feat(prepare-image): Ensure /usr/bin/env is always present

This is required by common patterns in shell scripts.

There are some caveats around this. Adding logic to filter whether
coreutils is included in an image would slow down the Nix evaluation,
so the link is currently created even in cases where it doesn't point
to anything.

Fixes #109
---
 prepare-image/prepare-image.nix | 12 ++++++++++++
 1 file changed, 12 insertions(+)

diff --git a/prepare-image/prepare-image.nix b/prepare-image/prepare-image.nix
index 316bfbb..56f9e7a 100644
--- a/prepare-image/prepare-image.nix
+++ b/prepare-image/prepare-image.nix
@@ -132,6 +132,18 @@ let
   contentsEnv = symlinkJoin {
     name = "bulk-layers";
     paths = allContents.contents;
+
+    # Ensure that there is always a /usr/bin/env for shell scripts
+    # that require it.
+    #
+    # Note that images which do not actually contain `coreutils` will
+    # still have this symlink, but it will be dangling.
+    #
+    # TODO(tazjin): Don't link this if coreutils is not included.
+    postBuild = ''
+      mkdir -p $out/usr/bin
+      ln -s ${coreutils}/bin/env $out/usr/bin/env
+    '';
   };
 
   # Image layer that contains the symlink forest created above. This