bug#48500: 28.0.50; url-retrieve-synchronously exits abnormally due to pending keyboard input from terminal

[Eli Zaretskii]

> From: Shane Mulligan <mullikine@gmail.com>
> Date: Wed, 19 May 2021 18:48:09 +1200
> 
> I may have resolved this issue with the following patch to 
> `url-retrieve-synchronously`.
> What this achieves is to trigger a `quit` in a controlled environment rather 
> than allowing it to occur when
> `accept-process-output` is run.
> It's not always wanted to trigger a quit when `(input-pending-p)` is `t`. But 
> I noticed from placing
> `while-no-input` around `accept-process-output` to avoid the `quit` that 
> `url-retrieve-synchronously` would
> then hang but with the controlled `quit` happening beforehand, 
> `accept-process-output` no longer needs
> `while-no-input` around it. The end result is buttery smooth helm with no 
> accidental `quit` from typing too
> fast. I think this may have resulted in GUI helm faster too.

Thanks, but what causes a quit in the first place?