FIX: queue heartbeats in readonly modes

If sidekiq is paused or Discourse is in readonly continue to queue
heartbeats

If we do not do that then a master process can end up reaping sidekiq
workers and causing various badness

This also impacts restore which can do weird stuff TM in cases like this

app/jobs/base.rb

@@ -183,10 +183,11 @@ module Jobs
     extend MiniScheduler::Schedule
 
     def perform(*args)
-      return if Discourse.readonly_mode?
+      if (Jobs::Heartbeat === self) || !Discourse.readonly_mode?
         super
       end
     end
+  end
 
   def self.enqueue(job_name, opts = {})
     klass = "Jobs::#{job_name.to_s.camelcase}".constantize

lib/sidekiq/pausable.rb

@@ -74,7 +74,7 @@ class Sidekiq::Pausable
   end
 
   def call(worker, msg, queue)
-    if Sidekiq.paused?
+    if Sidekiq.paused? && !(Jobs::RunHeartbeat === worker)
       worker.class.perform_in(@delay, *msg['args'])
     else
       start = Process.clock_gettime(Process::CLOCK_MONOTONIC)

spec/components/sidekiq/pausable_spec.rb

@@ -2,10 +2,35 @@ require 'rails_helper'
 require_dependency 'sidekiq/pausable'
 
 describe Sidekiq do
+  after do
+    Sidekiq.unpause!
+  end
+
   it "can pause and unpause" do
     Sidekiq.pause!
     expect(Sidekiq.paused?).to eq(true)
     Sidekiq.unpause!
     expect(Sidekiq.paused?).to eq(false)
   end
+
+  it "can still run heartbeats when paused" do
+    Sidekiq.pause!
+
+    freeze_time 1.week.from_now
+
+    jobs = Sidekiq::ScheduledSet.new
+
+    Sidekiq::Testing.disable! do
+      jobs.clear
+
+      middleware = Sidekiq::Pausable.new
+      middleware.call(Jobs::RunHeartbeat.new, { "args" => [{}] }, "critical") do
+        "done"
+      end
+
+      jobs = Sidekiq::ScheduledSet.new
+      expect(jobs.size).to eq(0)
+    end
+
+  end
 end

spec/jobs/heartbeat_spec.rb

@@ -0,0 +1,19 @@
+require 'rails_helper'
+require_dependency 'jobs/base'
+
+describe Jobs::Heartbeat do
+  after do
+    Discourse.disable_readonly_mode
+  end
+
+  it "still enqueues heartbeats in readonly mode" do
+    freeze_time 1.week.from_now
+
+    Discourse.enable_readonly_mode
+
+    Sidekiq::Testing.inline! do
+      Jobs::Heartbeat.new.perform(nil)
+      expect(Jobs::RunHeartbeat.last_heartbeat).to eq(Time.new.to_i)
+    end
+  end
+end