Invalid emit for class+namespace using module=commonJs in TS 3.9

[mjbvz]

TypeScript Version: 3.9.0-dev.20200228

Search Terms:

• export
• namespace

Code
With target = ES2017, module = commonJS

export class Color {
    static readonly x = new Color();
}

export namespace Color {
    export const a = 1
}

Expected behavior:
In TS 3.8, this emits:

Object.defineProperty(exports, "__esModule", { value: true });
class Color {
}
exports.Color = Color;
Color.x = new Color();
(function (Color) {
    Color.a = 1;
})(Color = exports.Color || (exports.Color = {}));

Actual behavior:
In TS 3.9, this emits:

Object.defineProperty(exports, "__esModule", { value: true });
const Color = /** @class */ (() => {
    class Color {
    }
    Color.x = new Color();
    return Color;
})();
exports.Color = Color;
(function (Color) {
    Color.a = 1;
})(Color = exports.Color || (exports.Color = {}));
exports.Color = Color;

Which is not valid since it tries to reassign a constant value: Color = exports.Color

• TS 3.8.2
• TS 3.9

[mjbvz]

/cc Ryan Cavanaugh (@RyanCavanaugh) This blocks using TS 3.9 for building VS Code

[mjbvz]

Ron Buckton (@rbuckton) Possibly introduced by #36795

[weswigham]

Ack, this is probably my fault - as a follow up to the community PR, I updated it to use const, thinking it was more desirable - I didn't realize we relied on the ability to reassign the class declaration later on (even if we're reassigning it to itself in most cases). Regressed by #36907.