$PSNativeCommandUseErrorActionPreference does not work when error stream is discarded

[sharpchen]

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Steps to reproduce

I don't see documentation describe this behavior? The doc only mentioned exit code.

& {
    $ErrorActionPreference = 'Continue'
    $PSNativeCommandUseErrorActionPreference = $true

    # expected error:
    robocopy 1>$null # NativeCommandExitException: Program "Robocopy.exe" ended with non-zero exit code: 16 (0x00000010).

    # error discarded:
    robocopy 1>$null 2>$null # no error
    robocopy 1>$null 2>&1 # effectively discarded, so no error

    # not discarded
    robocopy 2>&1 # NativeCommandExitException: Program "Robocopy.exe" ended with non-zero exit code: 16 (0x00000010).
}

Expected behavior

Only exit code matters for the action

Actual behavior

err stream affects the action

Error details

Environment data

Name                           Value
----                           -----
PSVersion                      7.6.2
PSEdition                      Core
GitCommitId                    7.6.2
OS                             Microsoft Windows 10.0.19045
Platform                       Win32NT
PSCompatibleVersions           {1.0, 2.0, 3.0, 4.0…}
PSRemotingProtocolVersion      2.4
SerializationVersion           1.1.0.1
WSManStackVersion              3.0

Visuals

No response

[237dmitry]

If set $ErrorActionPreference = SilentlyContinue then cp 2>&1 works as expected stderr outputs to stdout. But I do not understand why the foreground color is red ($LASTEXITCODE is not equal to 0?).

$  & {                                               
          $ErrorActionPreference = 0
          $PSNativeCommandUseErrorActionPreference = $true
          
          cp 2>&1
     }
# $PSStyle.Formatting.Error color:
cp: missing file operand
Try '/usr/bin/cp --help' for more information.

[rhubarb-geek-nz]

Just a theory, how is the exit code of a native program reported?

PowerShell cmdlets themselves don't have such a thing as an exit code. Is the exit code packaged as a record in the error stream?

[mklement0]

The behavior looks correct to me, based on the following:

• PowerShell reflects the process exit code of the most recently executed external (native) program in its automatic $LASTEXITCODE variable, irrespective of the value of the $PSNativeCommandUseErrorActionPreference preference variable

• The purpose of $PSNativeCommandUseErrorActionPreference is to emit a non-terminating error immediately after an external program signals (putative) failure via a nonzero exit code, noting the failure and the specific exit code.
  As with any PowerShell error, whether it surfaces (visibly) is governed by the $ErrorActionPreference preference variable

That is, while it is the exit code that matters with respect to whether the NativeCommandExitException error is emitted, that error can be silenced or suppressed, using the usual techniques.

---

On a broader note: The fact that the error emitted is a non-terminating one (despite its name), is quite unfortunate; see:

• Native error handling: $PSNativeCommandUseErrorActionPreference = $true unexpectedly causes non-terminating, not statement-terminating errors #18368

[sharpchen]

I see, it's a mechanism works on both cmdlet and executables, I didn't know that, TIL.
It feels like equivalent to SilentlyContinue.

& {
    $ErrorActionPreference = 'Continue'
    Get-Item foo 2>$null # no error
    $? # False
}

I think it make sense for suppressing error message, it just no longer a pure error stream from the executable which is not very intuitive.

& {
    $ErrorActionPreference = 'Continue'
    $PSNativeCommandUseErrorActionPreference = $true

    robocopy 1>$null 2>err.log

    Get-Content err.log # NativeCommandExitException: Program "Robocopy.exe" ended with non-zero exit code: 16 (0x00000010).
}