Add proper setting for toggling Flexmailer on traditional mailings

[totten]

Before

When you enable Flexmailer, it is used for new-style mailings (e.g. Mosaico). However, it is not used to deliver traditional mailings.

There is a hidden/undocumented setting (experimentalFlexMailerEngine) to toggle this. The setting has primarily been used for automated testing, but it has also been communicated to other developers/implementers.

After

• There is a setting flexmailer_traditional which dictates whether Flexmailer will try to process traditional mailings.
• The setting is exposed in a new admin form.
• The old hidden setting experimentalFlexMailerEngine is mostly removed. However, if you have flexmailer_traditional=auto, it will fallback and obey experimentalFlexMailerEngine.

Comments

The automated tests rely on some forms of this setting to work correctly.

Additionally, to make sure that every form was tried in a realistic way, I used these manual steps:

• Setup a test site. Enable Flexmailer with this patch. Configure outbound mail to go an SMTP simulator (eg mailcatcher).
• Locally, hack Civi\FlexMailer\Listener\BasicHeaders to set $mailParams['X-Flexmailer'] = 'Yes';. This way, you can determine which engine sent a message by inspecting the headers.
• Prepare a draft mailing.
• Check: Does CiviMail's test/preview functionality work?
  • Repeat this procedure for each value of flexmailer_traditional (auto, bao, flexmailer):
    • Set flexmailer_traditional to the desired value
    • Preview as text
    • Preview as HTML
    • Send test email to one address
    • Send test email a group
• Submit the test mailing. Save a DB snapshot (e.g. civibuild snapshot dmaster --snapshot dm-send)
• Check: Does delivery work?
  • Repeat this procedure for each value of flexmailer_traditional (auto, bao, flexmailer):
    • Restore DB
    • Set flexmailer_traditional to the desired value
    • Run the delivery
    • Check the resulting messages
    • (Ex: civibuild restore dmaster --snapshot dm-send && cv flush && cv api setting.create flexmailer_traditional=THE_VALUE && cv api -U admin job.process_mailing)

To work completely, depends on #38. However, that's a preexisting issue, and it mostly works without.

[totten]

Rebased. Also updated to use more objective terminology (e.g. bao instead of legacy).

Re-tested on current CiviCRM 5.13-RC branch.

civicrm-core   flexmailer              mosaico || mos-preview  mos-send-test   mos-submit       mos-anon        || trad-preview trad-send-test  trad-submit     trad-anon
-------------------------------------------------------------------------------------------------------------------------------------------------------------------------
5.13           master-setting[auto]    2.x     || OK            OK              OK              OK*             || OK           OK              OK              Fail
5.13           master-setting[flx]     2.x     || OK            OK              OK              OK*             || OK           OK              OK              OK*
5.13           master-setting[bao]     2.x     || OK            OK              OK              OK*             || OK           OK              OK              Fail

Definitions:

• mos-*: Tested with Mosaico mailing
• trad-*: Tested with traditional mailing
• *-preview: In CiviMail composition UI, use "Preview" buttons. Check a few contact+action+mailing tokens.
• *-send-test: In CiviMail composition UI, use "Send Test" button. Check a few contact+action+mailing tokens. Check for presence/absence of X-Flexmailer header.
• *-submit: Submit the mailing. Run the cron job. Check a few contact+action+mailing tokens. Check for presence/absence of X-Flexmailer header.
• *-anon: View the sent mailing in a browser as an anonymous user

So it generally looks good, except for the otherwise known/open issues around anonymously viewing a mailing in a browser.