bug#52751: 27.1; Go back to editing the from part in query replace

[Juri Linkov]

> I often run into the situation of doing a complicated query replace/regexp,
>  submitting the FROM part and then during editing the TO part I notice an
> error in FROM. But I cannot go back there to fix it, I can either cancel
> the replace which deletes the FROM part, because it did not yet go into
> history, or I can submit some dummy TO value, cancel the replace, restart
> it  and then use history to fix the FROM value.
>
> There should be an easy way to go back to editing FROM without cumbersome
> workarounds.
>
> Mainstream UIs solve this by having different input fields where I can
> switch to and edit any input field before submitting. Maybe the FROM -> TO
> input should be the default with a preinserted -> arrow, so the user can
> switch back an forth easily between FROM and TO?

Preinserting an arrow by default would be confusing for users.
But maybe M-n could insert it.