Linux/Mac/VT: PSReadline in PowerShell 7 rc3 goes ballistic if you do not respond to its request for cursor position

[DHowett-MSFT]

Environment

PS version: 7.0.0-rc.3
PSReadline version: 2.0.0
os: Linux antares 5.4.0-4-amd64 #1 SMP Debian 5.4.19-1 (2020-02-13) x86_64 GNU/Linux
PS file version: 7.0.0.0
HostName: ConsoleHost
BufferWidth: 120
BufferHeight: 50

Also happens in Azure Cloud; this is likely in the Unix compat layer.

Steps to reproduce

Use a terminal emulator that does not respond to CSI 6 n (DSR Device Status Report 6, Cursor Position).
Launch powershell. Wait.

Expected behavior

It doesn't explode.

Actual behavior

It dumps random memory to the output stream, then just exits.

[daxian-dbw]

PSReadLine depends on querying for the cursor position to work properly.
What would be the expected behavior in those terminal emulator then?

[DHowett-MSFT]

I would expect it to not dump memory to the screen and then crash without a message, in any case!

Zsh doesn’t seem to need cursor position info to do highlighting. Do we really?

[daxian-dbw]

I would expect it to not dump memory to the screen and then crash without a message, in any case!

Very reasonable 😄

[SteveL-MSFT]

This seems like a .NET issue. The reason is that if you start pwsh -noninteractive which doesn't load PSRL, you get the same behavior. We should try to get a simplified repro for .NET team.

[DHowett-MSFT]

That doesn’t necessarily mean that it’s not PSReadline, right? Since it was unloaded, it’s not necessarily ruled out.

(I read the original message as though removing PSReadline helped 👍)

[DHowett-MSFT]

Sorry, disregard. I misread your message 😄

[SteveL-MSFT]

The .NET code in question is here.

[daxian-dbw]

It happens with pwsh -noninteractive because the built-in PowerShell console host code also query cursor position a lot.
So it seems this issue will happen as long as an application try getting the cursor position within such a terminal emulator.

Also happens in Azure Cloud; this is likely in the Unix compat layer.

@DHowett-MSFT I missed this comment. Can you please share a repro using Azure Cloud Shell?

[DHowett-MSFT]

So, Windows Terminal 0.9 (no later) doesn’t support cursor report. If you run pwsh from bash in the included Azure Cloud Shell profile, it’ll crash like this.