Pull Request for Issue #28682 .

See also #28614 (comment).

Summary of Changes

The getUpdatedFiles routine in file plugins/installer/override/override.php reads 2 filelists (before and after event) which should be arrays from session data into 2 variables and does only something if they have the same count of elements and there are differences in the elements. If so, it returns an arry with the different elements, otherwise it returns an empty array.

But there is no check if the file list has been ever stored in the session, i.e. if what is read from the session is an arry or not. This makes it fail with the PHP Warning mentioned in issue #28682 when updating Joomla 3.10 to 4.

The fix is to do nothing and return an empy array if one of the values read back from the session is not an array, like it would be if they had different count.

Testing Instructions

Code review should be sufficient.

But if you want to do a real test:

Test 1: Reproduce the issue

1. Make sure you can see PHP warnings in a log file by setting error reporting and error log in the right way in your PHP settings.

2. Update a 3.0-dev or current 3.10 nightly build to the latest 4.0-dev nigthly.

• For using "Live Update", set the update channel to "Custom URL" and minimum stability to "Development", and enter the regular nightly build's update URL https://update.joomla.org/core/nightlies/next_major_list.xml in the Joomla Update component's options.
• For using "Upload & Update" download the regular 4.0 nightly update package https://developer.joomla.org/nightlies/Joomla_4.0.0-beta1-dev-Development-Update_Package.zip.

3. At the end of the update, when loging in to the backend, watch the PHP or the webserver log (wherever your PHP logs errors to).

Result: See section "Actual result" below.

Test 2: Check that this PR solves it.

Repeat "Test 1: Reproduce the issue", but this time use the patched update package built for this PR.

• For "Live Update": Custom URL = https://ci.joomla.org/artifacts/joomla/joomla-cms/4.0-dev/28683/downloads/31294/pr_list.xml
• For "Upload & Update": Update package = https://ci.joomla.org/artifacts/joomla/joomla-cms/4.0-dev/28683/downloads/31294/Joomla_4.0.0-beta1-dev+pr.28683-Development-Update_Package.zip

Result: See section "Expected result" below.

Expected result

No PHP warning as mentioned in issue #28682 .

Actual result

PHP warning as mentioned in issue #28682 .

Documentation Changes Required

None.