Fix Private Messages self-quoting private posts being changed to followers-only (#36249)

app/services/post_status_service.rb

@@ -69,7 +69,7 @@ class PostStatusService < BaseService
     @text         = @options.delete(:spoiler_text) if @text.blank? && @options[:spoiler_text].present? && @quoted_status.blank?
     @visibility   = @options[:visibility] || @account.user&.setting_default_privacy
     @visibility   = :unlisted if @visibility&.to_sym == :public && @account.silenced?
-    @visibility   = :private if @quoted_status&.private_visibility?
+    @visibility   = :private if @quoted_status&.private_visibility? && %i(public unlisted).include?(@visibility&.to_sym)
     @scheduled_at = @options[:scheduled_at]&.to_datetime
     @scheduled_at = nil if scheduled_in_the_past?
   rescue ArgumentError

spec/services/post_status_service_spec.rb

@@ -321,6 +321,14 @@ RSpec.describe PostStatusService do
     expect(status).to be_private_visibility
   end
 
+  it 'correctly preserves visibility for private mentions self-quoting private posts' do
+    account = Fabricate(:account)
+    quoted_status = Fabricate(:status, account: account, visibility: :private)
+
+    status = subject.call(account, text: 'test', quoted_status: quoted_status, visibility: 'direct')
+    expect(status).to be_direct_visibility
+  end
+
   it 'returns existing status when used twice with idempotency key' do
     account = Fabricate(:account)
     status1 = subject.call(account, text: 'test', idempotency: 'meepmeep')