wp-includes/class-wp-theme.php:767Determines whether the theme exists.
bool public function exists() { return ! ( $this->errors() && in_array( 'theme_not_found', $this->errors()->get_error_codes(), true ) ); }Introduced in 3.4.0. Unchanged from 6.7.7 through 7.1.0.
Signature, return type and hooks compared across 5 parsed releases.
src/wp-includes/class-wp-theme.php, and regenerated for each WordPress release so it tracks the code rather than a snapshot of it.