Up-Arrow crashes PowerShell (without PSReadLine)

[Jaykul]

In PowerShell in Bash on Ubuntu on Windows ...

Steps to reproduce

1. Up Arrow -- produces "A"
2. Remove-Module PSReadLine
3. Up Arrow
4. Up Arrow # will produce "Aborted (core dumped)"

Expected behavior

Up Arrow should navigate through history.

Actual behavior

Up Arrow types "A" or crashes PowerShell.

Environment data

> $PSVersionTable

Name                           Value
----                           -----
PSVersion                      5.1.10032.0
PSEdition                      PowerShellCore
PSCompatibleVersions           {1.0, 2.0, 3.0, 4.0...}
BuildVersion                   3.0.0.0
GitCommitId                    v6.0.0-alpha.7
CLRVersion
WSManStackVersion              3.0
PSRemotingProtocolVersion      2.3
SerializationVersion           1.1.0.1

[lzybkr]

We shouldn't crash, but don't expect good command line editing if you remove PSReadline on *nix systems.

[Jaykul]

Yeah, I only removed it because the arrow buttons were resulting in "A" "B" "C" "D" being inserted, and because of #1088 ... I figured it couldn't hurt to try and see. I was wrong ;-)

[andyleejordan]

@Jaykul we've had a lot of problems with not exactly correct TERM settings, as System.Console is a very new library on Linux, and so doesn't fallback well.

So to get down to the bottom of this, can you give me this information:

First I want to know for sure the key code being sent.

sudo showkey
< uparrow>
< enter >
< ctrl-c >

On my machine this shows me:

sudo showkey
kb mode was UNICODE
[ if you are trying this under X, it might not work
since the X server is also reading /dev/console ]

press any key (program terminates 10s after last keypress)...
^[[A
^Ccaught signal 2, cleaning up...

So my up arrow is sending the key code ^[ (escape) [A (and I imagine this is true for you; if it's not then things are very strange).

Next I want to see what your terminfo entry is for your current term, so translate ^[ into \E (escape in another form) and do this:

infocmp -L1 | grep -F '\E[A'

If all is well, it should report key_up=\E[A which System.Console should be interpreting correctly (as this is essentially all .NET does). If it's not key_up then we've found that your TERM isn't quite right; if it is key_up then it would seem something is wrong with System.Console.

I'm also curious what this gives in PowerShell:

[Console]::ReadKey()
< up arrow >

If everything is working right it'll be:

KeyChar     Key Modifiers
-------     --- ---------
       UpArrow         0

P.S. I agree with @lzybkr, it shouldn't crash. When < up arrow > is interpreted right, and PSReadLine is disabled, we simply discard it. PowerShell is definitely not receiving a ConsoleKeyInfo up arrow. I just don't yet know where it's gone wrong.

[Jaykul]

This is in (Bash on) Ubuntu on Windows...

root@DUO:~# sudo showkey
Couldn't get a file descriptor referring to the console

When I tried with [Console]::ReadKey() or $host.UI.RawUI.ReadKey() | Format-Table * -Force -Auto ... I'm getting VirtualKeyCode 27, Key "Escape" ...

[andyleejordan]

By Ubuntu on Windows, you mean WSL (as in, not a VM)?

If so, I'm surprised it's worked at all this far 😄

[jdhitsolutions]

If I remove PSReadline in a CentOS VM, up arrow doesn't crash anything. But I do lose tab completion. I'm assuming this means that PSReadline will practically be a requirement for Linux?

[lzybkr]

@jdhitsolutions - yes, the minimal viable (e.g. has tab completion, history) command line editing experience is really provided by PSReadline.

Unlike Windows, Linux doesn't provide an API for command line editing, that's really up to an application. GNU readline is the most widely used library, which PSReadline emulates and extends to more friendly to PowerShell and Windows, so it's not too valuable to add support for other command line editing libraries.

[Jaykul]

Yeah, @andschwa, WSL. Should I call it that, in the future? 😕

Anyway, it does not work very well at all, but yes, this crash is only there.

[andyleejordan]

@Jaykul For WSL issues, especially for .NET Core on WSL, we should follow up with BashOnWindows.