[RFE] G keybinding unifying C-c C-u, U, and g

[dcolascione]

Is your feature request related to a problem? Please describe.
I set mu4e-headers-auto-update to nil, so if I'm in the header list and waiting for a message to arrive, I have to hit C-c C-u to run mu4e-update-mail-and-index, then hit g to run mu4e-search-rerun to actually see any new mail that's arrived. This two step process is annoying.

Also, C-c C-u is an annoying keybinding. The more ergonomic U doesn't DWIM in the header view.

Describe the solution you'd like
I'd like to add a new G (i.e. S-g) keybinding to all of the mu4e main view, the header view, and the message view. We can define it to

1. do the same thing as mu4e-update-mail-and-index, and also, when that's done,
2. mu4e-search-rerun.

With prefix, we'd run in the background.

IOW, G would temporarily enable mu4e-headers-auto-update for one call to mu4e-update-mail-and-index.

G seems to be unused in all three modes, so we get one nice uniform interface to "check your email" in a DWIM way no matter where in mu4e you are and no matter your default setting of mu4e-headers-auto-update.

Describe alternatives you've considered

• Turning on mu4e-headers-auto-update isn't an option because it's even more annoying for the header list to appear to change unbidden.

• Defining keyboard macro for C-c C-u then g would work, but wouldn't let me run the refresh in the background.

• We could add another value to mu4e-headers-auto-update that would have mu4e update the header list only when no window is showing it (addressing the previous point), but doing so wouldn't quite solve my problem.

[djcb]

I'm a bit hesitant to add (more) very special-casy code to mu4e, but I think you could add a command, something like:

(defun my-update-and-index ()
  (interactive)
  (setq mu4e-headers-auto-update t)
  (mu4e-update-mail-and-index)) 

and then append something to mu4e-index-updated-hook (must be last) that
resets mu4e-headers-auto-update. You can get fancier, of course.

You can bind the command to your favorite key.