Fix TypeScript annotations for setters

[roboslone]

Currently there's no way to chain setters, because they don't return anything.
It would be convenient to have setters return the object they're called on:

// Current
const message = new Message()
message.setName('name')
message.setCount(1)

const subMessage = new SubMessage()
subMessage.setName('sub')
message.setSubMessage(subMessage)

// Proposed
const message = new Message()
    .setName('name')
    .setCount(1)
    .setSubMessage(new SubMessage().setName('sub'))

[roboslone]

UPD I've checked generated JS code and it seems that JS actually returns this. TypeScript annotations have void though.

/**
 * @param {string} value
 * @return {!proto.MyMessage} returns this
 */
proto.MyMessage.prototype.setSymbol = function(value) {
  return jspb.Message.setProto3StringField(this, 1, value);
};

export class MyMessage extends jspb.Message {
  setSymbol(value: string): void;
}

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[roboslone]

It's still relevant.

[reddaly]

The fix should be relatively easy. The file to modify is here: https://github.com/improbable-eng/ts-protoc-gen/blob/master/src/ts/message.ts