I prefer this because I almost never use sticky range selections. Also, this
fixes the issue that just clicking a line in a diff (without dragging) already
creates a range selection. It still does, technically, but it's no longer a
problem because a non-sticky one-line range selection behaves the same as a
non-range selection.
We're not fully standardising here: different contexts can store their range state however
they like. What we are standardising on is that now the view is always responsible for
highlighting the selected lines, meaning the context/controller needs to tell the view
where the range start is.
Two convenient benefits from this change:
1) we no longer need bespoke code in integration tests for asserting on selected lines because
we can just ask the view
2) line selection in staging/patch-building/merge-conflicts views now look the same as in
list views i.e. the highlight applies to the whole line (including trailing space)
I also noticed a bug with merge conflicts not rendering the selection on focus though I suspect
it wasn't a bug with any real consequences when the view wasn't displaying the selection.
I'm going to scrap the selectedRangeBgColor config and just let it use the single line
background color. Hopefully nobody cares, but there's really no need for an extra config.
Previously, when pressing right-arrow when the cursor is already in the last
hunk, it would jump back to the beginning of that hunk. This can be confusing if
the hunk is long, maybe the start of the hunk is already scrolled off the top of
the window, and then pressing right-arrow actually scrolls *backwards*, which is
counter-intuitive. It's better to do nothing in this case.
Same for left-arrow when the cursor is already in the first hunk, although here
the problem is not so severe (unless diff context was increased by a huge
amount, and the start of the first hunk is scrolled off the bottom of the
window).
Previously, the current line was only moved as much as necessary so that it's in
view again. This had the problem that when jumping downwards from hunk to hunk
with the right-arrow key, only the first line of the new hunk was shown at the
bottom of the window. I prefer to put the selected line in the middle of the
view in this case, so that I can see more of the newly selected hunk.
This has the consequence that when scrolling through the view line by line using
down-arrow, the view jumps by half a screen whenever I reach the bottom. I can
see how some users might be opposed to this change, but I happen to like it too,
because it allows me to see more context of what's ahead.
