Fix media not being marked sensitive when client sets a CW but no text (#13277)

Mastodon enforces the “sensitive” flag on media attachments whenever a toot
is posted with a Content Warning. However, it does so *after* potentially
converting the Content Warning to toot text (when there is no toot text),
which leads to inconsistent and surprising behavior for API clients.
This commit fixes this inconsistency.

app/services/post_status_service.rb

@@ -48,6 +48,7 @@ class PostStatusService < BaseService
   private
 
   def preprocess_attributes!
+    @sensitive    = (@options[:sensitive].nil? ? @account.user&.setting_default_sensitive : @options[:sensitive]) || @options[:spoiler_text].present?
     @text         = @options.delete(:spoiler_text) if @text.blank? && @options[:spoiler_text].present?
     @visibility   = @options[:visibility] || @account.user&.setting_default_privacy
     @visibility   = :unlisted if @visibility&.to_sym == :public && @account.silenced?
@@ -157,7 +158,7 @@ class PostStatusService < BaseService
       media_attachments: @media || [],
       thread: @in_reply_to,
       poll_attributes: poll_attributes,
-      sensitive: (@options[:sensitive].nil? ? @account.user&.setting_default_sensitive : @options[:sensitive]) || @options[:spoiler_text].present?,
+      sensitive: @sensitive,
       spoiler_text: @options[:spoiler_text] || '',
       visibility: @visibility,
       language: language_from_option(@options[:language]) || @account.user&.setting_default_language&.presence || LanguageDetector.instance.detect(@text, @account),

spec/services/post_status_service_spec.rb

@@ -79,6 +79,13 @@ RSpec.describe PostStatusService, type: :service do
     expect(status.spoiler_text).to eq spoiler_text
   end
 
+  it 'creates a sensitive status when there is a CW but no text' do
+    status = subject.call(Fabricate(:account), text: '', spoiler_text: 'foo')
+
+    expect(status).to be_persisted
+    expect(status).to be_sensitive
+  end
+
   it 'creates a status with empty default spoiler text' do
     status = create_status_with_options(spoiler_text: nil)