FIX: Make disabling TLS in mail possible again

Following the Rails 7 upgrade, the `DISCOURSE_SMTP_ENABLE_START_TLS`
setting doesn’t work anymore. This is because Rails upgraded the
`net-smtp` gem to the 0.3.1 version which enables `starttls` by default.
The `mail` gem doesn’t support this new behavior yet and doesn’t know
how to disable TLS. This should be fixed in an upcoming release.

Meanwhile applying this patch allows us to get back the previous
behavior which is expected by many.

Gemfile

@@ -41,7 +41,7 @@ gem 'actionview_precompiler', require: false
 
 gem 'seed-fu'
 
-gem 'mail', git: 'https://github.com/discourse/mail.git', require: false
+gem 'mail', git: 'https://github.com/discourse/mail.git'
 gem 'mini_mime'
 gem 'mini_suffix'
 

config/environments/production.rb

@@ -41,7 +41,7 @@ Discourse::Application.configure do
       settings[:tls] = true
     end
 
-    config.action_mailer.smtp_settings = settings.reject { |_, y| y.nil? }
+    config.action_mailer.smtp_settings = settings.compact
   else
     config.action_mailer.delivery_method = :sendmail
     config.action_mailer.sendmail_settings = { arguments: '-i' }

lib/freedom_patches/mail_disable_starttls.rb

@@ -0,0 +1,21 @@
+# frozen_string_literal: true
+
+# Patch from
+# https://github.com/rails/rails/issues/44698#issuecomment-1069675285 to enable
+# previous behavior with Net::SMTP regarding TLS.
+#
+# This should be fixed in an upcoming release of the Mail gem (probably 2.8),
+# when this patch is merged: https://github.com/mikel/mail/pull/1435
+module FreedomPatches::MailDisableStarttls
+  def build_smtp_session
+    super.tap do |smtp|
+      unless settings[:enable_starttls_auto]
+        if smtp.respond_to?(:disable_starttls)
+          smtp.disable_starttls
+        end
+      end
+    end
+  end
+
+  ::Mail::SMTP.prepend(self)
+end

spec/lib/freedom_patches/mail_disable_starttls_spec.rb

@@ -0,0 +1,23 @@
+# frozen_string_literal: true
+
+describe FreedomPatches::MailDisableStarttls do
+  subject(:smtp_session) { smtp.build_smtp_session }
+
+  let(:smtp) { Mail::SMTP.new(options) }
+
+  context "when the starttls option is not provided" do
+    let(:options) { {} }
+
+    it "doesn't disable starttls" do
+      expect(smtp_session).to be_starttls
+    end
+  end
+
+  context "when the starttls option is set to `false`" do
+    let(:options) { { enable_starttls_auto: false } }
+
+    it "properly disables starttls" do
+      expect(smtp_session).not_to be_starttls
+    end
+  end
+end