Troubleshooting a Drupal HTTP 500 when there are no error log messages

Question

I have reviewed some websites on how to troubleshoot HTTP 500 on a Drupal site and most often I have seen a PHP error by running drush ws in the console, however, I have been running into an oddity and I am not sure where to look to begin troubleshooting as this one doesn't throw HTTP 500.

I am not necessarily looking for someone to troubleshoot this bug specifically, and am not very good at writing/modifying any PHP, but it would be helpful to know how to identify the problem and fix it ... The problem only seems to occur when saving the field settings on a Taxonomy

Reproduction:

1. Have a Drupal site (latest core) with several modules installed (all up to date), and content types configured (not a fresh site). Running on Windows, IIS, MySQL, PHP 8.4 stack.

2. Create new content type (problem happens on existing too).

-- Define a name, but no other changes. I tried this with Boolean, text, taxonomy term ref - problem not isolated to one type.

-- Click save

-- Click save field settings

3. Receive HTTP 500

-- URL of the HTTP 500 after clicking Save Field Settings is /admin/structure/types/manage/test/fields/node.test.field_testref/storage?destinations%5B0%5D%5Broute_name%5D=entity.field_config.node_field_edit_form&destinations%5B0%5D%5Broute_parameters%5D%5Bfield_config%5D=node.test.field_testref&destinations%5B0%5D%5Broute_parameters%5D%5Bnode_type%5D=test&destinations%5B1%5D%5Broute_name%5D=entity.node.field_ui_fields&destinations%5B1%5D%5Broute_parameters%5D%5Bfield_config%5D=node.test.field_testref&destinations%5B1%5D%5Broute_parameters%5D%5Bnode_type%5D=test&destinations%5B2%5D=/admin/structure/types/manage/test/fields/add-field

-- Only this URL is erroring out - the site itself is accessible. If I navigate using Admin Toolbar to Structure > Content Types > Test it also does not error out and I am able to edit/save that created field fine.

4. Refreshed page, ran drush ws - no errors but the page still throws HTTP 500

5. Ran drush cr/updb, error still occurs

6. Nothing errors/warnings in Status Report/recent log messages

-- I do have one "notice" in log, but didnt seem relevant. Module sliderwidget has an entry in the system.schema key/value storage, but is missing from your site.

Answer 1

I assume, that you get 500 error with no information in your browser.

You can temporary activate display of all errors by adding the next lines in your sites/default/settings.php file:

// Show all errors.
$config['system.logging']['error_level'] = 'verbose';
error_reporting(E_ALL);
ini_set('display_errors', TRUE);
ini_set('display_startup_errors', TRUE);

This will give you a clue, where does the error happen.

In addition you can check server logs, as @cilefen commented.