Set function name for decorated private non-field elements

[JLHwung]

Q	A
Fixed Issues?	Part 2 of #16117
Patch: Bug Fix?
Major: Breaking Change?
Minor: New Feature?
Tests Added + Pass?	Yes
Documentation PR Link
Any Dependency Changes?
License	MIT

In this PR we introduced a new setFunctionName helper, used by the decorator runtime to set the function name for any decorated private non-field elements.

As a follow-up to #16139, this PR is the second part of #15122.

In the future, the setFunctionName helper will set the class name of any anonymous class expression so that its own class decorator can access the inferred class name from the NamedEvaluation, which is the last part of #15122.

[babel-bot]

Build successful! You can test your changes in the REPL here: https://babeljs.io/repl/build/55932/

[JLHwung]

The TS emits dedicated setFunctionName call here:

// input
class C {
  @dec static accessor #f = 1
}

// output
let C = (() => {
    var _a, _C_f_accessor_storage, _C_f_get, _C_f_set;
    let _staticExtraInitializers = [];
    let _static_private_f_decorators;
    let _static_private_f_initializers = [];
    let _static_private_f_descriptor;
    return _a = class C {
        },
        _C_f_get = function _C_f_get() { return _static_private_f_descriptor.get.call(this); },
        _C_f_set = function _C_f_set(value) { return _static_private_f_descriptor.set.call(this, value); },
        (() => {
            const _metadata = typeof Symbol === "function" && Symbol.metadata ? Object.create(null) : void 0;
            _static_private_f_decorators = [dec];
            /* ⬇️⬇️⬇️ __setFunctionName call here ⬇️⬇️⬇️ */
            __esDecorate(_a, _static_private_f_descriptor = { get: __setFunctionName(function () { return __classPrivateFieldGet(_a, _a, "f", _C_f_accessor_storage); }, "#f", "get"), set: __setFunctionName(function (value) { __classPrivateFieldSet(_a, _a, value, "f", _C_f_accessor_storage); }, "#f", "set") }, _static_private_f_decorators, { kind: "accessor", name: "#f", static: true, private: true, access: { has: obj => __classPrivateFieldIn(_a, obj), get: obj => __classPrivateFieldGet(obj, _a, "a", _C_f_get), set: (obj, value) => { __classPrivateFieldSet(obj, _a, value, "a", _C_f_set); } }, metadata: _metadata }, _static_private_f_initializers, _staticExtraInitializers);
            if (_metadata) Object.defineProperty(_a, Symbol.metadata, { enumerable: true, configurable: true, writable: true, value: _metadata });
            __runInitializers(_a, _staticExtraInitializers);
        })(),
        _C_f_accessor_storage = { value: __runInitializers(_a, _static_private_f_initializers, 1) },
        _a;
})();

Here we merge the setFunctionName call with the applyMemberDecs to optimize the output size.

[nicolo-ribaudo]

Given that the various decorators helpers are exclusive (and everything except for legacy and 2023-05) will be dropped in Babel 8, could we just inline the helper instead?

Or maybe we could even just fix this in 2023-05.

[JLHwung]

The helper is isolated because we will eventually emit setFunctionName when transforming the decorated anonymous class expression (Part 1 of #16117). For example

// input.js
function dec(target, context) {
  // print '[Symbol.iterator]'
  console.log(target.name);
}
class Dummy {
  [Symbol.iterator] = @dec class {}
}

to

// output.js
function dec(_, context) {
  // print '[Symbol.iterator]'
  console.log(context.name);
}
var computedKey = Symbol.iterator;
class Dummy {
  [computedKey] = (setFunctionName(class {
    static {
      [_decorated_class, _initClass] = _applyDecs(this, [], [dec]).c;
    }
    static {
      _initClass();
    }
  }, computedKey), _decorated_class);
}

In this example we will also pass a symbol, which is also a valid property key, to the setFunctionName helper.

Currently we have not implemented such transform yet. It was addressed in #15122 but I will open new PR to do so.

[nicolo-ribaudo]

In which case we are passing a symbol name to this helper?

[JLHwung]

See #16144 (comment).

[nicolo-ribaudo]

Ok 👍