For commit ff88a2a927 which fixed a regression caused by commit
e51ce12969.
I'm trying to provide enough guardrails for myself and future readers
without causing a combinatorial explosion in tests. The previous commit
was able to get more value out of existing tests, but this test feels
necessary. And useful in general without reference to a specific bug.
I'm being unprincipled at the moment between pos and x,y coordinates.
Whatever is more convenient. Perhaps a cleaner approach will come to me
over time.
I almost pushed this to production. That would have been catastrophic;
the very first keystroke anyone typed into the editor would have failed.
And in the process, this fixes the next bug on my TODO list! Paste on
first line wasn't working. Now it is.
When long wrapping lines go past the current page, I find myself
scrolling before I get to the bottom. So let's scroll less, usually from
the start of the bottom-most line, even if it wraps multiple screen
lines.
The challenge with this is to ensure that a long line that fills the
whole page by itself doesn't get you stuck. I take some care to make
sure <pagedown> always makes forward progress.
It's still a bit simple-minded. Most software will keep the first bound
fixed and move the second. Lines currently has the bounds in a queue of
sorts. But I have a test to indicate the behavior that is definitely
desired. We'll see if we need it to get more complex.