FEATURE: setting allowing tl0/anonymous flag illegal content (#30785)

The new site setting `allow_anonymous_and_tl0_to_flag_illegal` allows
tl0 users to flag illegal content. In addition, anonymous users are
instructed on how to flag illegal content by sending emails.

Also `email_address_to_report_illegal_content` setting is added. If not
provided, then the site contact email is used.

spec/lib/guardian_spec.rb

@@ -163,6 +163,16 @@ RSpec.describe Guardian do
       Flag.reset_flag_settings!
     end
 
+    it "return true for illegal if tl0 and allow_tl0_and_anonymous_users_to_flag_illegal_content" do
+      SiteSetting.flag_post_allowed_groups = ""
+      user.trust_level = TrustLevel[0]
+      expect(Guardian.new(user).post_can_act?(post, :illegal)).to be false
+
+      SiteSetting.email_address_to_report_illegal_content = "illegal@example.com"
+      SiteSetting.allow_tl0_and_anonymous_users_to_flag_illegal_content = true
+      expect(Guardian.new(user).post_can_act?(post, :illegal)).to be true
+    end
+
     it "works as expected for silenced users" do
       UserSilencer.silence(user, admin)
 

spec/lib/site_settings/validations_spec.rb

@@ -474,4 +474,19 @@ RSpec.describe SiteSettings::Validations do
       expect { validations.validate_twitter_summary_large_image(nil) }.not_to raise_error
     end
   end
+
+  describe "#validate_allow_tl0_and_anonymous_users_to_flag_illegal_content" do
+    it "does not allow to enable when no contact email is provided" do
+      expect {
+        validations.validate_allow_tl0_and_anonymous_users_to_flag_illegal_content("t")
+      }.to raise_error(
+        Discourse::InvalidParameters,
+        I18n.t("errors.site_settings.tl0_and_anonymous_flag"),
+      )
+      SiteSetting.contact_email = "illegal@example.com"
+      expect {
+        validations.validate_allow_tl0_and_anonymous_users_to_flag_illegal_content("t")
+      }.not_to raise_error
+    end
+  end
 end