From 7ee70fd479a3f915c25d101f6453a95807b0c5a4 Mon Sep 17 00:00:00 2001
From: Graham Christensen <graham@grahamc.com>
Date: Fri, 15 Nov 2019 11:01:22 -0500
Subject: [PATCH] mirror-nixos-branch.pl: exit 0 if the channel would go back
 in time

Prometheus now has a configured alert if an update job fails for a
while. Going back in time is not so unusual:

1. a hydra evaluation completes with some failed jobs
2. the channel advances to this commit
3. an admin restarts a failed job
4. the channel would go backward because the evaluation is complete

Since it is not a problem, make it a non-problematic exit code.
---
 mirror-nixos-branch.pl | 6 +++++-
 1 file changed, 5 insertions(+), 1 deletion(-)

diff --git a/mirror-nixos-branch.pl b/mirror-nixos-branch.pl
index cfcd88b..c40d8ee 100755
--- a/mirror-nixos-branch.pl
+++ b/mirror-nixos-branch.pl
@@ -77,7 +77,11 @@ my @curReleaseUrl = split(/\//, read_file("$channelsDir/$channelName", err_mode
 my $curRelease = pop @curReleaseUrl;
 my $d = `NIX_PATH= nix-instantiate --eval -E "builtins.compareVersions (builtins.parseDrvName \\"$curRelease\\").version (builtins.parseDrvName \\"$releaseName\\").version"`;
 chomp $d;
-die "channel would go back in time from $curRelease to $releaseName, bailing out\n" if $d == 1;
+if ($d == 1) {
+    warn("channel would go back in time from $curRelease to $releaseName, bailing out\n");
+    exit;
+}
+
 exit if $d == 0;
 
 if ($bucket->head_key("$releasePrefix")) {