Feedback providers should export a VT escape sequence for other Terminals

[StevenBucher98]

Summary of the new feature / enhancement

In order to have extra UI or visual changes when feedback providers trigger in PowerShell in other terminals, i.e VSCode terminal, we need way to indicate to the terminal in a general way to notify a feedback provider triggered. We should have a VT escape sequence to notify other terminals, or at least have some logic to determine we are in VSCode and output that sequence when feedback providers trigger.

Proposed technical implementation details (optional)

Output a VT escape sequence with every feedback provider

[rhubarb-geek-nz]

$env:TERM_PROGRAM -eq 'vscode' tells you that.

More generally, $host.UI.SupportsVirtualTerminal provides this information for any given host('s current configuration).

Neither mechanism gets through SSH automatically to a remote session, whereas the TERM environment variable does get forwarded.

PS> $host.UI.SupportsVirtualTerminal
True
PS> invoke-command -HostName foo -ScriptBLock { $host.UI.SupportsVirtualTerminal }
False
PS> $env:TERM='bar'
PS> ssh foo
$ echo $TERM
bar

[mklement0]

Good point about the commands I mentioned only working locally (not also in remoting sessions).

the TERM environment variable does get forwarded.

That is true if you use the ssh utility, but If you enter an interactive session via Enter-PSSession -HostName foo, TERM is not set.

• As an aside: If PowerShell is the default shell for the targeted user, something like
  TERM=xterm-mono ssh jdoe@someserver (ditto for TERM=dumb) results in a broken interactive experience at least on macOS; see also (your own issue): PowerShell on osx - how to force to be completely monochrome PSReadLine#3918

While $host.UI.SupportsVirtualTerminal is always $false in a remote PowerShell session,
$PSStyle.OutputRendering still defaults to Host in the absence of a TERM variable, and PowerShell commands do produce colored output.

It is debatable whether this is the right default and arguably Enter-PSSession too should set TERM, but, leaving that aside, user code that produces strings for the interactive command-line editing experience could base its decision as to whether to use VT/ANSI escape sequences on $PSStyle.OutputRendering -in 'Host', 'Ansi'