FEATURE: Enables support for dark mode emails (#16520)

This PR enables custom email dark mode styles by default that were added here.

There is currently poor support for dark mode queries in mail clients. The main beneficiary of these changes will be Apple Mail and Outlook.

Enjoy the darkness 🕶️

app/helpers/email_helper.rb

@@ -29,8 +29,8 @@ module EmailHelper
     EmailStyle.new.html
       .sub('%{email_content}') { capture { yield } }
       .gsub('%{html_lang}', html_lang)
-      .gsub('%{dark_mode_meta_tags}', SiteSetting.dark_mode_emails_active ? dark_mode_meta_tags : "")
-      .gsub('%{dark_mode_styles}', SiteSetting.dark_mode_emails_active ? dark_mode_styles : "")
+      .gsub('%{dark_mode_meta_tags}', dark_mode_meta_tags)
+      .gsub('%{dark_mode_styles}', dark_mode_styles)
       .html_safe
   end
 

config/site_settings.yml

@@ -283,9 +283,6 @@ basic:
     type: enum
     enum: "ColorSchemeSetting"
     client: true
-  dark_mode_emails_active:
-    default: false
-    hidden: true    
   relative_date_duration:
     client: true
     default: 30

lib/email/styles.rb

@@ -238,7 +238,7 @@ module Email
 
       onebox_styles
       plugin_styles
-      dark_mode_styles if SiteSetting.dark_mode_emails_active
+      dark_mode_styles
 
       style('.post-excerpt img', "max-width: 50%; max-height: #{MAX_IMAGE_DIMENSION}px;")
 

spec/integration/email_style_spec.rb

@@ -72,7 +72,7 @@ describe EmailStyle do
         SiteSetting.default_email_in_reply_to = true
 
         expect(mail_html.scan('<h1 style="color: red;">FOR YOU</h1>').count).to eq(1)
-        matches = mail_html.match(/<div style="([^"]+)">#{post.raw}/)
+        matches = mail_html.match(/<div style="([^"]+)" dm=\"body\">#{post.raw}/)
         expect(matches[1]).to include('color: #FAB;') # custom
         expect(matches[1]).to include('padding-top:5px;') # div.body
       end

spec/lib/email/styles_spec.rb

@@ -157,10 +157,6 @@ describe Email::Styles do
   end
 
   context "dark mode emails" do
-    before do
-      SiteSetting.dark_mode_emails_active = true
-    end
-
     it "adds dark_mode_styles when site setting active" do
       frag = html_fragment('<div class="body">test</div>')
       styler = Email::Styles.new(frag)