Syntax error prompt does not work when prompt function is defined in profile or launch command and uses Write-Host

Environment

# Tested in 3 environments

PS version: 5.1.18362.628
PSReadline version: 2.0.1
os: 10.0.18362.1 (WinBuild.160101.0800)
PS file version: 10.0.18362.1 (WinBuild.160101.0800)
HostName: ConsoleHost (Windows Terminal)
BufferWidth: 229
BufferHeight: 55

PS version: 7.0.1
PSReadline version: 2.0.0
os: 10.0.18362.1 (WinBuild.160101.0800)
PS file version: 7.0.1.0
HostName: ConsoleHost (Windows Terminal)
BufferWidth: 229
BufferHeight: 55

PS version: 7.0.0
PSReadline version: 2.0.0
os: Linux 4.4.0-18362-Microsoft #476-Microsoft Fri Nov 01 16:53:00 PST 2019 x86_64 x86_64 x86_64 GNU/Linux
PS file version: 7.0.0.0
HostName: ConsoleHost
BufferWidth: 229
BufferHeight: 55

Exception report

None

Steps to reproduce

Write a prompt function that uses Write-Host to construct the prompt. Place the prompt function in your PowerShell profile or in the -Command option script block when launching PowerShell. Doing so will cause PSReadLine’s syntax error prompt notification color to not trigger.

# C:\users\<username>\Documents\WindowsPowerShell\profile.ps1

# Prompt function that uses Write-Host to construct prompt
function prompt {
    Write-Host 'myprompt' -NoNewLine
    '> ' # Need to also return string so PowerShell doesn't auto add "PS>"
}

Expected behavior

PS C:\> powershell.exe -NoLogo
PS C:\> function prompt { Write-Host 'myprompt' -NoNewLine; '> ' }
myprompt> } # syntax error prompt works

Actual behavior

PS C:\> powershell.exe -NoExit -Command { function prompt { Write-Host 'myprompt' -NoNewLine; '> ' } }
myprompt> } # last char of prompt does not change color with syntax error

All Examples

[lzybkr]

Add the following to your profile - I think it should fix it:

Set-PSReadLineOption -PromptText '> '

Before v2, PSReadLine relied on screen scraping to implement the error prompt coloring. With the move to a more portable PSReadLine, screen scraping was no longer an option.

If you have a “pure” prompt, PSReadLine can infer what text needs to change to properly change the color, but if your prompt is not pure, e.g. calls Write-Host, then you need to help PSReadLine out with this configuration option.

Note that if your prompt is extra fancy (like mine):

You can also specify the error coloring precisely by passing 2 strings instead of one - the first being the normal text, the second being the error text, so mine looks like:

$esc = [char]0x1b
$pc = [char]0xe0b0
$fg = "0"
$nbg = "8;2;95;158;160"
$ebg = "1"

Set-PSReadLineOption -PromptText (
    "$esc[4${nbg};3${fg}mPS$esc[4${fg};3${nbg}m$pc",
    "$esc[4${ebg};3${fg}mPS$esc[4${fg};3${ebg}m$pc"
)

Note how I use the background color instead of the foreground color.

[lzybkr]

@DecoyJoe - yeah, I see the same thing with the ? but hadn’t investigated. It looks like you need to set the output encoding to UTF8:

[Console]::OutputEncoding = [System.Text.Encoding]::UTF8

I thought PSReadLine was doing that for you, but maybe that changed. @daxian-dbw?