magento/magento2#18323: Order confirmation email for guest checkout d…

[swnsma]

Description

Fix save of downloadable links for guest checkout.
During research was found another issue: #19034 which the main reason that problem has appeared.
Events are moved from 'save_commit_after' to 'save_after' to resolve the issue and keep downloadable links save in scope of Sales Order Save transaction.

Fixed Issues (if relevant)

1. Order confirmation email for guest checkout does not include download links #18323: Order confirmation email for guest checkout does not include download links
2. salesInvoiceOrder REST API does not make downloadable products available #19003: salesInvoiceOrder REST API does not make downloadable products available

Manual testing scenarios (*)

Please see issue: #18323

Contribution checklist (*)

• Pull request has a meaningful description of its purpose
• All commits are accompanied by meaningful commit messages
• All new or changed code is covered with unit/integration tests (if applicable)
• All automated tests passed successfully (all builds on Travis CI are green)

[magento-engcom-team]

Hi @swnsma. Thank you for your contribution
Here is some useful tips how you can test your changes using Magento test environment.
Add the comment under your pull request to deploy test or vanilla Magento instance:

• @magento-engcom-team give me test instance - deploy test instance based on PR changes
• @magento-engcom-team give me $VERSION instance - deploy vanilla Magento instance

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[magento-engcom-team]

Hi @VladimirZaets, thank you for the review.
ENGCOM-3385 has been created to process this Pull Request

[magento-engcom-team]

Hi @swnsma. Thank you for your contribution.
We will aim to release these changes as part of 2.2.8.
Please check the release notes for final confirmation.

Please, consider to port this solution to 2.3 release line.
You may use Porting tool to port commits automatically.