Treat empty markdown and html strings as valid cached text, not missing cache...

Treat empty markdown and html strings as valid cached text, not missing cache that needs to be updated

app/models/concerns/cache_markdown_field.rb

@@ -85,8 +85,7 @@ module CacheMarkdownField
   def cached_html_up_to_date?(markdown_field)
     html_field = cached_markdown_fields.html_field(markdown_field)
 
-    cached = cached_html_for(markdown_field).present? && __send__(markdown_field).present? # rubocop:disable GitlabSecurity/PublicSend
-    return false unless cached
+    return false if cached_html_for(markdown_field).nil? && !__send__(markdown_field).nil? # rubocop:disable GitlabSecurity/PublicSend
 
     markdown_changed = attribute_changed?(markdown_field) || false
     html_changed = attribute_changed?(html_field) || false

changelogs/unreleased/optimize-issues-avoid-noop-empty-cache-updates2.yml

+---
+title: Treat empty markdown and html strings as valid cached text, not missing cache
+  that needs to be updated
+merge_request:
+author:
+type: performance

spec/models/concerns/cache_markdown_field_spec.rb

@@ -102,6 +102,26 @@ describe CacheMarkdownField do
     it { expect(thing.cached_markdown_version).to eq(CacheMarkdownField::CACHE_VERSION) }
   end
 
+  context 'when a markdown field is set repeatedly to an empty string' do
+    it do
+      expect(thing).to receive(:refresh_markdown_cache).once
+      thing.foo = ''
+      thing.save
+      thing.foo = ''
+      thing.save
+    end
+  end
+
+  context 'when a markdown field is set repeatedly to a string which renders as empty html' do
+    it do
+      expect(thing).to receive(:refresh_markdown_cache).once
+      thing.foo = '[//]: # (This is also a comment.)'
+      thing.save
+      thing.foo = '[//]: # (This is also a comment.)'
+      thing.save
+    end
+  end
+
   context 'a non-markdown field changed' do
     before do
       thing.bar = 'OK'