TypeScript: Tagged template literals compiled incorrectly, TemplateStringsArray not cached

TypeScript Version: 2.4.1

Code

let previousStrings;

function test(strings, ...value) {
  if (previousStrings !== undefined && previousStrings !== strings) {
    window.alert('failure');
  }
  previousStrings = strings;
}

function go(n) {
  return test`literal ${n}`;
}

Expected behavior:

According to the ECMAScript spec, every time a template tag is evaluated, the same strings object should be passed as the first argument:

Each TemplateLiteral in the program code of a realm is associated with a unique template object that is used in the evaluation of tagged Templates (12.2.9.6). The template objects are frozen and the same template object is used each time a specific tagged Template is evaluated.

https://tc39.github.io/ecma262/#sec-gettemplateobject

Actual behavior:

The above snippet compiles to:

var previousStrings;
function test(strings) {
    var value = [];
    for (var _i = 1; _i < arguments.length; _i++) {
        value[_i - 1] = arguments[_i];
    }
    if (previousStrings !== undefined && previousStrings !== strings) {
        window.alert('failure');
    }
    previousStrings = strings;
}
function go(n) {
    return (_a = ["literal ", ""], _a.raw = ["literal ", ""], test(_a, n));
    var _a;
}

You can see that _a is going to have a new identity for each call of go().

FWIW, Babel compiles this correctly:

'use strict';

var _templateObject = _taggedTemplateLiteral(['literal ', ''], ['literal ', '']);

function _taggedTemplateLiteral(strings, raw) { return Object.freeze(Object.defineProperties(strings, { raw: { value: Object.freeze(raw) } })); }

var previousStrings = void 0;

function test(strings) {
  if (previousStrings !== undefined && previousStrings !== strings) {
    window.alert('failure');
  }
  previousStrings = strings;
}

function go(n) {
  return test(_templateObject, n);
}

This is breaking lit-html when used in TypeScript: https://github.com/PolymerLabs/lit-html/issues/58