1503716 - [autoconfig] Convert code to use async functions and Promises

Status: ASSIGNED

(Thunderbird :: Account Manager, enhancement)

Description

[Ben Bucksch (:BenB)]

The account creation dialog code is mostly asynchronous processing. Written 9 years ago, there were no Promise or async/await available. So, it uses the closest match: successCallback and errorCallback. It uses that pattern consistently throughout (aside from the UI), so it should be reasonably straightforward to convert to Promises and |async function|s. Callers should use |await| where possible/reasonable.

To consider here is that most async functions currently return an |Abortable| object. That will still be needed despite Promises, because it's important that both the end user and the dialog logic can cancel any request at any time. Obviously, the |Abortable| object is needed immediately when the function starts, not when it finishes, so it can't be the result of the Promise. We need to find a nice function API so that these functions can run as await foo(), but still be abortable.

Out of scope:
* It currently uses its own small FetchHTTP class based on XMLHttpRequest. I have already tried to convert this to Fetch(), but that brings no advantage and does not work well, so this is out of scope here. XMLHttpRequest serves us fine here. The library should be to Promise / async function, though, which should be straight-forward and simple.
* Any other code polish, code style etc. I may fix some code style in lines that I touch, but if reviewers ask me to change lines in some way or other "because you touch them anyway", this task here will not be feasible. Other code polish outside of the conversion to Promises should be put in a different bug and be done there, not here.

Comment 1

[Ben Bucksch (:BenB)]

Code dependency on bug 1500105, because that changes a lot of the code.

Comment 2

[Ben Bucksch (:BenB)]

xref bug 1504805 for |class| syntax.