Dries Buytaert recently published a great post on how to prepare for Drupal 9. He explains how we build Drupal 9 in Drupal 8 using deprecations and the tools to use to detect use of deprecated code. Acquia funded me and Zoltán Herczog to work on one of the tools in the past few weeks. Zoltán just released the second alpha of Upgrade Status. It is definitely worth a try!
Here is how it works:
The module provides an overview of all the contributed and custom projects you have on a Drupal 8 site. It groups custom modules based on the directory structure and takes contributed projects from the update module. For contributed projects it also displays the available updates information inline. This is because if you keep contributed modules up to date, they should eventually improve Drupal 9 compatibility. We also plan to allow project maintainers to inform users about the best way to engage with them on the way to Drupal 9. This is dependent on new project fields on drupal.org which we plan to use to pull information to this dashboard.
Looking at the project list, the UI allows you to run a report on all of the projects to find any known Drupal 9 incompatibilities. Because running the full report takes a really long time, the UI also allows you to run reports on projects one by one. Or rerun the report on specific projects as you are working on improving their codebase. You can export the full report and each report individually.
The reporting backend and the report output is based entirely on the fantastic work of Matt Glaman on drupal-check at Centarro (formerly Commerce Guys) which is in itself based on phpstan by Ondřej Mirtes. We use the same tools that are used in drupal-check, the best command line tool available to check for deprecation errors (and other code quality issues). If you plan to include Drupal 9 compatibility checking in your build or continuous integration system, then drupal-check is your best bet.
Matt is also working with Ondřej to include the @deprecation annotation text in errors, which would improve the usefulness of the reporting of both tools immensely. Until then Upgrade Status links to api.drupal.org for documentation where you can find the deprecation documentation as well and learn about how to fix it.
The alpha2 version of the module was just released including support for recovering from PHP fatal errors (that legitimately happen in parsing some projects), as well as better chunking of project parsing so huge projects like Drupal Commerce will not result in timeouts or memory limit issues. We plan to improve the interactive experience further as well as fix any bugs reported, so please keep the reports coming. Looking forward to your experience with Upgrade Status!