From 334bb6100bdd1a5664275eae5d5c0a7062e5e1cf Mon Sep 17 00:00:00 2001
From: zimbatm <zimbatm@zimbatm.com>
Date: Mon, 2 Nov 2020 12:35:39 +0100
Subject: [PATCH] idempotent installation

Don't run the installer if Nix has already been installed on the host.
We assume that the installed Nix is already in the desired state.

This allows to share a given pipeline between hosted and self-hosted
runners. Usually the self-hosted runners are long-lived and already have
Nix installed.
---
 lib/install-nix.sh | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/lib/install-nix.sh b/lib/install-nix.sh
index 9b2e240..d4a3b9a 100755
--- a/lib/install-nix.sh
+++ b/lib/install-nix.sh
@@ -1,6 +1,11 @@
 #!/usr/bin/env bash
 set -euo pipefail
 
+if type -p nix &>/dev/null ; then
+  echo "Aborting: Nix is already installed at $(type -p nix)"
+  exit
+fi
+
 # Configure Nix
 add_config() {
   echo "$1" | sudo tee -a /tmp/nix.conf >/dev/null