functions.php

<?php

if ( ! function_exists( 'plugin_basename_main_file' ) ) {
	/**
	 * Gets plugin folder and main file.
	 * Example result: Core-Functionality/core-functionality.php
	 *
	 * `plugin_basename()` returns main plugin file only when called from that file.
	 * This function works from within any plugin file.
	 *
	 * @return  string
	 */
	function plugin_basename_main_file() {

		$current_path = plugin_basename( __FILE__ );
		$plugin_folder = substr( $current_path, 0, strpos( $current_path, '/' ) );
		$plugin_file = key( get_plugins( '/' . $plugin_folder ) );

		return $plugin_folder . '/' . $plugin_file;

	}
}