7.0.0-preview.2 PSReadLine stops working after Get-Help or other commands

[eedwards-sk]

Overview

Certain (possibly just full-screen overlayed) commands or operations cause PSReadLine to stop working afterwards, and in some cases, for the console (process) to become completely unresponsive.

I have a reliable reproduction below, although it only reproduces one aspect of the problem I've surfaced (I don't have a reliable repro for the console becoming unresponsive).

Steps to reproduce

pwsh-preview -NoProfile
help Get-Alias
(press 'q' to quit)
(press Up-Arrow / Down-Arrow to cycle through history)

Expected behavior

History is cycled

Actual behavior

History is not cycled / input sometimes unresponsive

Environment data

Name                           Value
----                           -----
PSVersion                      7.0.0-preview.2
PSEdition                      Core
GitCommitId                    7.0.0-preview.2
OS                             Darwin 18.7.0 Darwin Kernel Version 18.7.0: Thu Jun 20 18:42:21 PDT 2019; root:xnu-4903.270.47~4/RELEASE_X86_64
Platform                       Unix
PSCompatibleVersions           {1.0, 2.0, 3.0, 4.0…}
PSRemotingProtocolVersion      2.3
SerializationVersion           1.1.0.1
WSManStackVersion              3.0

[eedwards-sk]

Strangely, I noticed that Get-Help Get-Alias works differently than help Get-Alias

help Get-Alias opens a multiple-line scrollable view of the help text, whereas Get-Help Get-Alias just dumps it out all at once on screen

So whatever the behavior is that does the fullscreen scrollable view (help Get-Alias) is what seems to break PSReadLine

[eedwards-sk]

I confirmed that help Get-Alias seems to open the help text for Get-Alias using linux less (confirmed since I can press h and see less help commands)

So something about how it's opening less is breaking PSReadLine ?

[eedwards-sk]

I also discovered that running a sub-instance of pwsh-preview from the 'broken' state, and then exiting that shell, fixes the issue.

e.g. after reproducing the above, then:

pwsh-preview
exit

allows the original pwsh-preview session to page up/down through history again

[eedwards-sk]

Confirmed that I can repro just by doing

echo "foo" | less

or

echo "foo" | more

from inside a pwsh-preview prompt

after exiting less or more as per above, none of the arrow keys work for moving the cursor, and I can't use shortcuts like alt+arrow to move the cursor across words, etc.

[SteveL-MSFT]

I can repro this easily. Doing a cls to clear the screen seems to make it work again.

[SteveL-MSFT]

So what appears to be happening is that after you exit less, the up arrow is received as the VT100 escape sequence {ESC}A which PSReadLine doesn't treat as the up arrow (this is true for all for arrow keys, you can't go left for example). Clearing the screen seems to reset the terminal so the arrow keys are received as just arrow keys. Seems like this might be an issue in corefx.

[SteveL-MSFT]

This looks like a regression in .NET Core 3.0. Using 6.2.1 w/ same PSReadLine doesn't repro. I'll have to see about getting them a simpler repro.

[marcinsmialek]

I had similar issues after invoking any command with completion which triggered scrolling,

[daxian-dbw]

Just checked that the .NET Core fix is not included in .NET Core Preview 9.