WP_Theme::get_template_directory()

Source

File: wp-includes/class-wp-theme.php

public function get_template_directory() {
		if ( $this->parent() ) {
			$theme_root = $this->parent()->theme_root;
		} else {
			$theme_root = $this->theme_root;
		}

		return $theme_root . '/' . $this->template;
	}