Improve temporary variables for decorators

[liuxingbaoyu]

Q	A
Fixed Issues?	Fixes #1, Fixes #2
Patch: Bug Fix?
Major: Breaking Change?
Minor: New Feature?
Tests Added + Pass?	Yes
Documentation PR Link
Any Dependency Changes?
License	MIT

before

var _initClass, _dec, _dec2, _dec3, _dec4, _dec5, _dec6, _dec7, _dec8, _initProto;
const dec = () => {};
_dec = call();
_dec2 = chain.expr();
_dec3 = arbitrary + expr;
_dec4 = array[expr];
_dec5 = call();
_dec6 = chain.expr();
_dec7 = arbitrary + expr;
_dec8 = array[expr];
let _Foo;
class Foo {
  static {
    [_initProto, _Foo, _initClass] = babelHelpers.applyDecs(this, [[[dec, _dec5, _dec6, _dec7, _dec8], 2, "method"]], [dec, _dec, _dec2, _dec3, _dec4]);
  }
  constructor(...args) {
    _initProto(this);
  }
  #a;
  method() {}
  makeClass() {
    var _dec9, _init_bar;
    return _dec9 = this.#a, class Nested {
      static {
        [_init_bar] = babelHelpers.applyDecs(this, [[_dec9, 0, "bar"]], []);
      }
      bar = _init_bar(this);
    };  
}
  static {
    _initClass();
  }
}

after:

var _initClass, _classDecs, _dec, _dec2, _dec3, _dec4, _initProto;
const dec = () => {};
_classDecs = [dec, call(), chain.expr(), arbitrary + expr, array[expr]];
_dec = call();
_dec2 = chain.expr();
_dec3 = arbitrary + expr;
_dec4 = array[expr];
let _Foo;
class Foo {
  static {
    [_initProto, _Foo, _initClass] = babelHelpers.applyDecs(this, [[[dec, _dec, _dec2, _dec3, _dec4], 2, "method"]], _classDecs);
  }
  constructor() {
    _initProto(this);
  }
  #a;
  method() {}
  makeClass() {
    var _dec5, _init_bar;
    return _dec5 = this.#a, class Nested {
      static {
        [_init_bar] = babelHelpers.applyDecs(this, [[_dec5, 0, "bar"]], []);
      }
      bar = _init_bar(this);
    };
  }
  static {
    _initClass();
  }
}

In addition, some class reference variable naming logic has been improved.

[babel-bot]

Build successful! You can test your changes in the REPL here: https://babeljs.io/repl/build/56145/

[nicolo-ribaudo]

Can we do the same for method decorators, other than class decorators?

[liuxingbaoyu]

I tried it, but it's a little complicated.
Because the order of memoise is inconsistent with the order of execution.
I haven't read the spec yet, but current testing is like this, the saved decorator function will be based on the order of the fields from front to back, and the decorator execution will be based on the ordering of the different types of groupings.

[JLHwung]

Changes summary:

1. Memoise the array of class decorators. This can reduce the number of required memoisers when there are multiple class decorators.

2. Create temporary inner class binding uid from the class binding name, either provided by the class name or from the named evaluation.

[JLHwung]

Nit: How about memoiseInPlace? And if memoiseInPlace is true, the return value of this function should be false since decorator expressions have already been memoised.

maybeExtractDecorators is used twice: one is in class decorator and the other is in element decorator. At this moment we could have avoided the default parameter and pass the memoiseInPlace explicitly.

[nicolo-ribaudo]

Great!