Warning: Invalid argument supplied for foreach() in system_get_date_formats() (line 3838 of system.module)

[klonos]

This was reported by Dennis Tran in our Zulip chat, as an error thrown during updating a D7 Ubercart site to Backdrop:

Warning: Invalid argument supplied for foreach() in system_get_date_formats() (line 3838 of /var/www/backdrop.test/htdocs/core/modules/system/system.module).

The warning seems harmless, and the same user reported that it didn't seem to break anything, but we should nevertheless test the D7 to Backdrop upgrade, and make sure that date formats are being properly converted to config.

Some related issues: #530 #840 #974
...and a change record re the system_get_date_formats() function: https://api.backdropcms.org/change-records/systemgetdateformats-return-value-has-changed

[indigoxela]

I suppose at that point of the upgrade no date formats have been set yet in system.date.json. It could possibly be a race condition, but that needs further digging.

This is the relevant code part.

    $date_formats = config_get('system.date', 'formats');
    foreach ($date_formats as $name => $format) {
      $date_formats[$name]['name'] = $name;
    }

If config_get() returned NULL, a loop will fail.

Additionally (unrelated here), the return value of function system_get_date_formats() is actually "mixed". If a requested format isn't found it returns FALSE.