Menu completion doesn't work properly when scrolling happens

[daxian-dbw]

Prerequisites

• Write a descriptive title.
• Make sure you are able to repro it on the latest released version
• Search the existing issues, especially the pinned issues.

Exception report

No exception report.

Screenshot

Environment data

PS Version: 7.1.3
PS HostName: ConsoleHost (Windows Terminal)
PSReadLine Version: 2.2.0-beta4
PSReadLine EditMode: Windows
OS: 10.0.19041.1 (WinBuild.160101.0800)
BufferWidth: 133
BufferHeight: 30

Steps to reproduce

1. Press Enter a number of times until the prompt is at the last line of the terminal window
2. Copy and paste the following command to the terminal: $instMods = (Get-InstalledModule | ConvertTo-Html | pandoc12.exe --from=html-auto_identifiers-native_spans-native_divs --to=gfm-gfm_auto_identifiers) -replace [reg] $env:HOMEPATH ,"`$env:HOMEPATH"
3. Move cursor to the closing bracket ] of the [reg].
4. Press Ctrl+Space to trigger the menu completion
5. Move the selection to RegisterPSSessionConfigurationCommand

Here is the GIF for reproducing this:

Expected behavior

The menu completion should work correctly when moving selection around, even though necessary screen scrolling is needed.

Actual behavior

As is shown, the menu completion rendering is broken in this case, where screen buffer scrolling was needed when initially rendering the menu.

[daxian-dbw]

The root cause of the issue in this case lies in the following code:

PSReadLine/PSReadLine/Completion.cs

Line 534 in 203d55c

PreviousTop = bufferEndPoint.Y;

PSReadLine/PSReadLine/Completion.cs

Lines 516 to 517 in 203d55c

	// if the menu has moved, we need to clear the lines under it
	if (bufferEndPoint.Y < PreviousTop)

PreviousTop should be set with the actual Top value before changing the Top value. And to decide whether menu has moved, we should compare the current Top with PreviousTop, instead of using bufferEndPoint.Y, which is a snapshot value that doesn't get updated when screen buffer scrolls.

[ghost]

🎉 This issue was addressed in 2949, which has now been successfully released in v2.2.0-beta5. 🎉