Description:
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When triggering an error using the attached test script, EG(current_execute_data) is NULL in zend_error_va() just before calling zend_error_cb and the error observers. This prevents error handlers from calling zend_fetch_debug_backtrace() which needs EG(current_execute_data) to produce the backtrace.

Calling zend_fetch_debug_backtrace() from inside an error callback did work in PHP 7.4 and returned the backtrace where the error was triggered.

Test script:
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<?php
ini_set('display_errors', false);
non_existant_function();