wp-includes/class-wp-query.php:4801Determines whether the query is the main query.
bool public function is_main_query() { global $wp_the_query; return $wp_the_query === $this; }Introduced in 3.3.0. Unchanged from 6.7.7 through 7.1.0.
Signature, return type and hooks compared across 5 parsed releases.
src/wp-includes/class-wp-query.php, and regenerated for each WordPress release so it tracks the code rather than a snapshot of it.