What is being checked for upgrade compatibility checks

[counterpoint]

Joomla 4 to Joomla 5 displays information about extension compatibility. What exactly determines the results?

When it says "no compatibility information", where is Joomla looking, and for what?

What exactly triggers the message "potential upgrade issue"?

[AMurray]

This should answer your questions: See https://docs.joomla.org/Pre-Update_Check.

Noting there is a pre-update check for 3.10 to 4.x and 4.x to 5.x as the upgrade paths are different; you can't for instance go from 3.10.x to 5.x you have to go to 4.x first.

[ceford]

Two places to look:

In System / Extensions you will see the Version number of each extension. This comes from its Manifest file on installation.

In System / Update / Update Sites you will see a list of extension update sites. Select a link to an update site (not the link to edit the site). You will see an xml file containing details of the current version.

Compatibility information is an optional parameter in the xml file. If present it may require a specific version of PHP, for example 8.2. For the update check Joomla fetches each xml file to compare the version number with the currently installed version and it will report any compatibility mismatch with your installation.

[counterpoint]

Thanks. I have a couple of concerns.

Extensions can be listed as "Potential upgrade issue". There is a link for more information, but that is only standard text. How can one discover what is being identified as a potential upgrade issue?

A lot of extensions are listed as "Update Information Unavailable". But these are modules and plugins that were automatically installed by components. The list is liable to confuse a user. It would be an impractical maintenance overhead to provide an update file for every individual module and plugin. Is there any solution for this to remove the potentially misleading clutter?