DEV: Add a helper method to clear every possible theme cache (#17585)

Our theme system is very complex and it can take a while to figure out how to invalidate the various types of caches that are used throughout the theme system. So, having a single helper method that invalidates everything can be useful in emergency situations where there is no time to read through the code and figure out how to clear the various caches.

Internal ticket: t64732.

spec/lib/discourse_spec.rb

@@ -472,4 +472,128 @@ describe Discourse do
     end
   end
 
+  context ".clear_all_theme_cache!" do
+    before do
+      setup_s3
+      SiteSetting.s3_cdn_url = "https://s3.cdn.com/gg"
+      stub_s3_store
+    end
+
+    let!(:theme) { Fabricate(:theme) }
+    let!(:upload) { Fabricate(:s3_image_upload) }
+    let!(:upload_theme_field) do
+      Fabricate(
+        :theme_field,
+        theme: theme,
+        upload: upload,
+        type_id: ThemeField.types[:theme_upload_var],
+        target_id: Theme.targets[:common],
+        name: "imajee",
+        value: "",
+      )
+    end
+    let!(:basic_html_field) do
+      Fabricate(
+        :theme_field,
+        theme: theme,
+        type_id: ThemeField.types[:html],
+        target_id: Theme.targets[:common],
+        name: "head_tag",
+        value: <<~HTML
+          <script type="text/discourse-plugin" version="0.1">
+            console.log(settings.uploads.imajee);
+          </script>
+        HTML
+      )
+    end
+    let!(:js_field) do
+      Fabricate(
+        :theme_field,
+        theme: theme,
+        type_id: ThemeField.types[:js],
+        target_id: Theme.targets[:extra_js],
+        name: "somefile.js",
+        value: <<~JS
+          console.log(settings.uploads.imajee);
+        JS
+      )
+    end
+    let!(:scss_field) do
+      Fabricate(
+        :theme_field,
+        theme: theme,
+        type_id: ThemeField.types[:scss],
+        target_id: Theme.targets[:common],
+        name: "scss",
+        value: <<~SCSS
+          .something { background: url($imajee); }
+        SCSS
+      )
+    end
+
+    it "invalidates all JS and CSS caches" do
+      Stylesheet::Manager.clear_theme_cache!
+
+      old_upload_url = Discourse.store.cdn_url(upload.url)
+
+      head_tag_script = Nokogiri::HTML5.fragment(
+        Theme.lookup_field(theme.id, :desktop, "head_tag")
+      ).css('script').first
+      head_tag_js = JavascriptCache.find_by(digest: head_tag_script[:src][/\h{40}/]).content
+      expect(head_tag_js).to include(old_upload_url)
+
+      js_file_script = Nokogiri::HTML5.fragment(
+        Theme.lookup_field(theme.id, :extra_js, nil)
+      ).css('script').first
+      file_js = JavascriptCache.find_by(digest: js_file_script[:src][/\h{40}/]).content
+      expect(file_js).to include(old_upload_url)
+
+      css_link_tag = Nokogiri::HTML5.fragment(
+        Stylesheet::Manager.new(theme_id: theme.id).stylesheet_link_tag(:desktop_theme, 'all')
+      ).css('link').first
+      css = StylesheetCache.find_by(digest: css_link_tag[:href][/\h{40}/]).content
+      expect(css).to include("url(#{old_upload_url})")
+
+      SiteSetting.s3_cdn_url = "https://new.s3.cdn.com/gg"
+      new_upload_url = Discourse.store.cdn_url(upload.url)
+
+      head_tag_script = Nokogiri::HTML5.fragment(
+        Theme.lookup_field(theme.id, :desktop, "head_tag")
+      ).css('script').first
+      head_tag_js = JavascriptCache.find_by(digest: head_tag_script[:src][/\h{40}/]).content
+      expect(head_tag_js).to include(old_upload_url)
+
+      js_file_script = Nokogiri::HTML5.fragment(
+        Theme.lookup_field(theme.id, :extra_js, nil)
+      ).css('script').first
+      file_js = JavascriptCache.find_by(digest: js_file_script[:src][/\h{40}/]).content
+      expect(file_js).to include(old_upload_url)
+
+      css_link_tag = Nokogiri::HTML5.fragment(
+        Stylesheet::Manager.new(theme_id: theme.id).stylesheet_link_tag(:desktop_theme, 'all')
+      ).css('link').first
+      css = StylesheetCache.find_by(digest: css_link_tag[:href][/\h{40}/]).content
+      expect(css).to include("url(#{old_upload_url})")
+
+      Discourse.clear_all_theme_cache!
+
+      head_tag_script = Nokogiri::HTML5.fragment(
+        Theme.lookup_field(theme.id, :desktop, "head_tag")
+      ).css('script').first
+      head_tag_js = JavascriptCache.find_by(digest: head_tag_script[:src][/\h{40}/]).content
+      expect(head_tag_js).to include(new_upload_url)
+
+      js_file_script = Nokogiri::HTML5.fragment(
+        Theme.lookup_field(theme.id, :extra_js, nil)
+      ).css('script').first
+      file_js = JavascriptCache.find_by(digest: js_file_script[:src][/\h{40}/]).content
+      expect(file_js).to include(new_upload_url)
+
+      css_link_tag = Nokogiri::HTML5.fragment(
+        Stylesheet::Manager.new(theme_id: theme.id).stylesheet_link_tag(:desktop_theme, 'all')
+      ).css('link').first
+      css = StylesheetCache.find_by(digest: css_link_tag[:href][/\h{40}/]).content
+      expect(css).to include("url(#{new_upload_url})")
+    end
+  end
 end