function normalizeEcmaVersion(parser, ecmaVersion) {
	if (isEspree(parser)) {
		if (ecmaVersion === "latest") {
			return espree.latestEcmaVersion;
		}
	}

	/*
	 * Calculate ECMAScript edition number from official year version starting with
	 * ES2015, which corresponds with ES6 (or a difference of 2009).
	 */
	return ecmaVersion >= 2015 ? ecmaVersion - 2009 : ecmaVersion;
}
Normalize ECMAScript version from the initial config
@param {Parser} parser The parser which uses this options.
@param {number} ecmaVersion ECMAScript version from the initial config
@returns {number} normalized ECMAScript version