From d7b48d0229dee31f22dedde0fd7550c51de10f78 Mon Sep 17 00:00:00 2001
From: David Taylor <david@taylorhq.com>
Date: Fri, 18 Feb 2022 08:51:14 +0000
Subject: [PATCH] FIX: Handle `nil` values in `DistributedCache#defer_get_set`
 (stable) (#15980)

Themes often cache `nil` values in a DistributedCache. This bug meant that we were re-calculating some values on every request, AND triggering message-bus publishing on every request.

This fix should provide a significant performance improvement for busy sites.
---
 lib/distributed_cache.rb           |  2 +-
 spec/lib/distributed_cache_spec.rb | 31 ++++++++++++++++++++++++++++++
 2 files changed, 32 insertions(+), 1 deletion(-)
 create mode 100644 spec/lib/distributed_cache_spec.rb

diff --git a/lib/distributed_cache.rb b/lib/distributed_cache.rb
index 2597c0a3e5..89e6058d11 100644
--- a/lib/distributed_cache.rb
+++ b/lib/distributed_cache.rb
@@ -21,7 +21,7 @@ class DistributedCache < MessageBus::DistributedCache
   end
 
   def defer_get_set(k, &block)
-    return self[k] if self[k]
+    return self[k] if hash.key? k
     value = block.call
     self.defer_set(k, value)
     value
diff --git a/spec/lib/distributed_cache_spec.rb b/spec/lib/distributed_cache_spec.rb
new file mode 100644
index 0000000000..91f0022a29
--- /dev/null
+++ b/spec/lib/distributed_cache_spec.rb
@@ -0,0 +1,31 @@
+# frozen_string_literal: true
+
+require 'rails_helper'
+
+describe "DistributedCache extensions" do
+  let(:cache) { DistributedCache.new('mytest') }
+
+  it "can defer_get_set" do
+    messages = MessageBus.track_publish("/distributed_hash") do
+      cache.defer_get_set("key") { "value" }
+    end
+    expect(messages.size).to eq(1)
+    expect(cache["key"]).to eq("value")
+  end
+
+  it "works correctly for nil values" do
+    block_called_counter = 0
+    messages = MessageBus.track_publish("/distributed_hash") do
+      2.times do
+        cache.defer_get_set("key") do
+          block_called_counter += 1
+          nil
+        end
+      end
+    end
+
+    expect(block_called_counter).to eq(1)
+    expect(messages.size).to eq(1)
+    expect(cache["key"]).to eq(nil)
+  end
+end