Declare template objects inline

[nicolo-ribaudo]

Q	A
Fixed Issues?
Patch: Bug Fix?
Major: Breaking Change?
Minor: New Feature?
Tests Added + Pass?	Yes
Documentation PR Link
Any Dependency Changes?
License	MIT

Template literal objects are cached globally per source location, so they cannot be evaluated twice.
We were solving this by using a singleton function defined in the top-level scope, but we can remove the functions and use cachedObject || (cachedObject = ...) inline, where cachedObject is a variable in the top-level scope.

This PR makes the output smaller when using terser, since the function and return keyword cannot be minified away with function declarations.

---

Input code:

foo`ab`;
foo`a${x}b`;

Output code (`main`):

function _templateObject2() {
  var data = babelHelpers.taggedTemplateLiteral(["a", "b"]);

  _templateObject2 = function _templateObject2() {
    return data;
  };

  return data;
}

function _templateObject() {
  var data = babelHelpers.taggedTemplateLiteral(["ab"]);

  _templateObject = function _templateObject() {
    return data;
  };

  return data;
}

function _taggedTemplateLiteral(strings, raw) { if (!raw) { raw = strings.slice(0); } return Object.freeze(Object.defineProperties(strings, { raw: { value: Object.freeze(raw) } })); }

foo(_templateObject());
foo(_templateObject2(), x);

Output code (this PR):

var _templateObject, _templateObject2;

foo(_templateObject || (_templateObject = babelHelpers.taggedTemplateLiteral(["ab"])));
foo(_templateObject2 || (_templateObject2 = babelHelpers.taggedTemplateLiteral(["a", "b"])), x);

Output code (`main` + terser): 211 bytes

function e(){var r=babelHelpers.taggedTemplateLiteral(["a","b"]);return e=function(){return r},r}function r(){var e=babelHelpers.taggedTemplateLiteral(["ab"]);return r=function(){return e},e}foo(r()),foo(e(),x);

Output code (this PR + terser): 123 bytes

var e,a;foo(e||(e=babelHelpers.taggedTemplateLiteral(["ab"]))),foo(a||(a=babelHelpers.taggedTemplateLiteral(["a","b"])),x);

---

[babel-bot]

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[nicolo-ribaudo]

I'm running the test262-pr job just in case, to be 100% sure that this doesn't break anything.

[nicolo-ribaudo]

There are some failing tests, but they are all caused by the test runner and not by Babel itself.

The test runner handles eval as if it was a different file, so Babel injects two temp variables with the same name: https://github.com/tc39/test262/blob/main/test/language/expressions/tagged-template/cache-differing-expressions-eval.js