Clear-Host fails to clear the first line

[brantburnett]

Environment

Windows build number: 10.0.19041.0
Windows Terminal version: 0.10.761.0

Any other software?
PowerShell Core 7.0.0
NodeJS 12.16.1
coronavirus-tracker-cli 0.6.0 (`npm install -g coronavirus-tracker-cli@0.6.0`)

Steps to reproduce

1. Open PowerShell Core
2. Run corona to get output
3. Run cls to clear the screen

Expected behavior

Screen should be fully cleared.

Actual behavior

The first line retains some characters. This is probably related to the color formatting being used by the CLI. The characters retained are also not from the line that was originally the topmost line.

Output before clearing:

Output after clearing:

Note: A second cls finishes clearing the screen.

[DHowett-MSFT]

This is really strange. Would you mind running a quick test for me?

Can you do this from Powershell Core outside of Terminal? To reproduce the same conditions as Terminal runs in, you will need to run this first (it will delete and temporarily disable your scrollback, but this is an important part of the repro!)

$Host.UI.RawUI.BufferSize = $Host.UI.RawUI.WindowSize

[brantburnett]

@DHowett

I performed the following steps (version of coranavirus-tracker-cli on npmjs.com has some issues with upstream API sources, so I pulled latest master):

1. Pulled latest source from https://github.com/sagarkarira/coronavirus-tracker-cli (b5f2f7e26bb98df0e47f7ebd3dcb6899d30d9409)
2. npm install
3. npm ./bin/index.js followed by cls in Windows Terminal to confirm the problem is still present
4. Switched to running PowerShell Core 7.0.0 directly, and ran $Host.UI.RawUI.BufferSize = $Host.UI.RawUI.WindowSize
5. npm ./bin/index.js followed by cls

The problem did not appear when running directly in PowerShell Core, only in Windows Terminal hosted PowerShell Core.

[DHowett-MSFT]

Yeah, alright, I can definitely reproduce this. Gotta fix for v1.

Notes to future debuggers:

When I run clear in powershell, this is what I get out of the pty.

␛[m␛[25l␛[94m␍␊␛[H(␛[m␍␊␛[K␍␊␛[K␍␊␛[K␍␊␛[K␍␊␛[K␍␊␛[K␍␊␛[K␍␊␛[K␍␊␛[K␍␊␛[K␍␊␛[K␍␊␛[K␍␊␛[K␍␊␛[K␍␊␛[K␍␊␛[K␍␊␛[K␍␊␛[K␍␊␛[K␍␊␛[K␍␊␛[K␍␊␛[K␍␊␛[K␍␊␛[K␍␊␛[K␍␊␛[K␍␊␛[K␍␊␛[K␍␊␛[K␛[1;2H␛[?25h␛[97mdhowett-sl␛[94m)␣␛[95m~␣␛[92m%␣

Weirdly enough, all those ESC [ K are coming through, but we don't end up clearing the line the prompt ends up on.