When we use the one panel for the entire commit message, its tricky to have a keybinding both for adding a newline and submitting.
By having two panels: one for the summary line and one for the description, we allow for 'enter' to submit the message when done from the summary panel,
and 'enter' to add a newline when done from the description panel. Alt-enter, for those who can use that key combo, also works for submitting the message
from the description panel. For those who can't use that key combo, and don't want to remap the keybinding, they can hit tab to go back to the summary panel
and then 'enter' to submit the message.
We have some awkwardness in that both contexts (i.e. panels) need to appear and disappear in tandem and we don't have a great way of handling that concept,
so we just push both contexts one after the other, and likewise remove both contexts when we escape.
This fixes two problems with the "amend commit with staged changes" command:
1. Amending to a fixup commit didn't work (this would create a commmit with the
title "fixup! fixup! original title" and keep that at the top of the branch)
2. Unrelated fixup commits would be squashed too.
The added integration test verifies that both of these problems are fixed.
It used to work on the assumption that rebasing commits in lazygit's model
correspond one-to-one to lines in the git-rebase-todo file, which isn't
necessarily true (e.g. when users use "git rebase --edit-todo" at the custom
command prompt and add a "break" between lines).
Previously we would have tried to do the rebase, resulting in a long and
somewhat cryptic error message from git; now we check ourselves and show a less
intimidating message.
If you ran this test enough times it would eventually fail; this happened
whenever the resulting squashed commit had a sha that happened to start with
"02". We test that "commit 02" does not appear in the diff window, but in that
case it did, at the very top of the window.
A better fix might be to change the commit message that we use in CreateNCommits
to something other than "commit XY", but that would require touching tons of
tests, so this is the easier fix.
It's not so much the total number of commits that matters here, it's just
whether we are on the first one. (This includes the other condition.)
This allows us to get rid of the condition in rebase.go.
