No error on this expressions in static property declaration initialisers (ESNext+useDefineForClassFields)

[sandersn]

No error on this expressions in static property declaration initialisers when targetting ESNext and with useDefineForClassFields. In this case the emit is correct and the types are correct, so the error should not be issued.

Addresses #36267 but only for ESNext+useDefineForClassFields.

[sandersn]

ping @elibarzilay @rbuckton

[rbuckton]

Have we considered changing our downlevel emit to support this case? We could either replace this with the class name depending on the context, or just wrap static initializers in something like:

(function() {
  Foo.t = this;
  Foo.at = () => this;
}).call(Foo);

Not necessary for this PR, but some food for thought.

[sandersn]

Yes, I thought a bit about changing the emit and had thought of rewriting to the class name, but not about the IIFE technique.

One consideration is that the error and emit have been this way forever and there's been little demand for the feature so far.

[Kingwl]

//// [awaitAndYieldInProperty.ts]
async function* test(x: Promise<string>) {
    class C {
        [await x] = await x;
        static [await x] = await x;

        [yield 1] = yield 2;
        static [yield 3] = yield 4;
    }

    return class {
        [await x] = await x;
        static [await x] = await x;

        [yield 1] = yield 2;
        static [yield 3] = yield 4;
    }
}

//// [awaitAndYieldInProperty.js]
async function* test(x) {
    var _a, _b, _c, _d, _e, _f, _g, _h, _j;
    class C {
        constructor() {
            this[_a] = await x;
            this[_c] = yield 2;
        }
    }
    _a = await x, _b = await x, _c = yield 1, _d = yield 3;
    (function () {
        C[_b] = await x; // here
        C[_d] = yield 4; // here
    }).call(C);
    return _j = class {
            constructor() {
                this[_e] = await x;
                this[_g] = yield 2;
            }
        },
        _e = await x,
        _f = await x,
        _g = yield 1,
        _h = yield 3,
        _j[_f] = await x,
        _j[_h] = yield 4,
        _j;
}

Seems we cannot just use IIFE-like expression because:

_a = await x, _b = await x, _c = yield 1, _d = yield 3;
    (function () {
        C[_b] = await x; // here
        C[_d] = yield 4; // here
    }).call(C);

[Kingwl]

It's not in await context anymore