Fix crash and rendering where large content is pasted to console on non-Windows

[Steve Lee (SteveL-MSFT)]

Several issues:

1. When large content is pasted to the console window on Windows, the buffer scrolls and PSReadLine now has a negative value for the cursor. Exception is raised when trying to set the cursor location to a negative y value. Fix is to check for this and set y to 0 (top).
2. When the buffer scrolls on paste, the re-rendering gets confused as it didn't track the scrolling appropriately. Fix is to skip drawing content that is off screen.
3. If the last line drawn to the screen is at the bottom of the screen buffer and the width of the output is exactly the window width, scroll doesn't happen until the next character is drawn; however, PSReadLine expected it to scroll so it's off by one. Fix here is to catch this and reset position back one line.

Fix#663

[Jason Shirk (lzybkr)]

I think the changes are fine, I'll try them out for a bit before merging.

Are you also going to fix MenuComplete? See this comment.

[Steve Lee (SteveL-MSFT)]

Jason Shirk (@lzybkr) that's a separate issue (able to repro with a large directory listing with my changes). I'll look at it in between other work as a separate PR.

[Jason Shirk (lzybkr)]

I'm on the fence with this fix. I'm not sure _initialY should be allowed to be negative, I do see other code that will misbehave under those conditions, e.g. ClearScreen.

Rendering is also still broken if you scroll up, e.g. press Home twice, you won't see the first line.

I think I've known about this general problem for so long that I'd forgotten about it, so it seems to come up rarely.

Is it now more important in some scenario I wasn't aware of? If not, I might be OK with the exception until the scenario is fixed completely. Of course at that point, we almost have a real text editor.

[Steve Lee (SteveL-MSFT)]

Jason Shirk (@lzybkr) it comes up easily on non-Windows when pasting a large script

[Jason Shirk (lzybkr)]

It happens easily on Windows as well, but you need a small window.

For my education and to better understand an appropriate fix - when are small console windows normally hit on non-Windows? I know that with no gui the window is small, but where else?

[Steve Lee (SteveL-MSFT)]

The default terminal size on Ubuntu is 80x24.

[Jason Shirk (lzybkr)]

Maybe it's reasonable to disallow a command line that exceeds the buffer height, at least until you can actually edit it properly.

[Steve Lee (SteveL-MSFT)]

Jason Shirk (@lzybkr) I think we should take this fix as even if you can't edit the buffer, it does show the syntax highlighting correctly making it easier to read. If you think we should explicitly disallow editing, I think we should have that as a separate issue. This PR does fix the current issue of an unhandled exception.

[Jason Shirk (lzybkr)]

I'm still on the fence about allowing _initialY to be negative. Before this PR, there was no code that expected that, this change basically takes the position that it is an expected condition, and we need to carefully review all other uses.

[Steve Lee (SteveL-MSFT)]

There aren't too many references to _initialY in the code. The menu code relies on _initialY and is probably the related crash for tab-complete for a large result set which I'll look into after we resolve this one. The alternative requires using a different variable to track how far off the screen we are.

[Jason Shirk (lzybkr)]

If we decide a negative _initialY is reasonable, the field declaration and where we change it should have comments saying as much and why.

[Jason Shirk (lzybkr)]

It would be good to add a test as well. The current console proxy does use a fixed buffer, but it might need some improvements to handle this scenario.

[Dongbo Wang (daxian-dbw)]

#979 has been merged as a more general fix to the ArgumentOutOfRangeException issue, so close this PR.