input processing methods (begin, process, end) do not share scope for trap statements

[poshAJ]

Prerequisites

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• Make sure you are able to repro it on the latest released version
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• Refer to the FAQ.
• Refer to Differences between Windows PowerShell 5.1 and PowerShell.

Steps to reproduce

about_Trap states that trap statements may be defined anywhere within a given scope, but always apply to all statements in that scope. When using input processing methods (begin, process, end), variables act as though there is a consistent scope however the trap statement does not. Below is an extended example of this action.

begin {
    Write-Output "Block is: begin"
    "Scope is: " + (Get-Variable -Name Scope -Scope Private -ErrorAction SilentlyContinue).Value
    "Set Scope to : " + (Set-Variable -Name Scope -Scope Private -Value "begin" -Option Private -PassThru).Value

    trap {
        Write-Output "Block is: trap"
        "Scope is: " + (Get-Variable -Name Scope -Scope Private -ErrorAction SilentlyContinue).Value
        "Set Scope to : " + (Set-Variable -Name Scope -Scope Private -Value "trap" -Option Private -PassThru).Value
        continue
    }
}

process {
    Write-Output "Block is: process"
    "Scope is: " + (Get-Variable -Name Scope -Scope Private -ErrorAction SilentlyContinue).Value
    "Set Scope to : " + (Set-Variable -Name Scope -Scope Private -Value "process" -Option Private -PassThru).Value

    throw "error"
}

end {
    Write-Output "Block is: end"
    "Scope is: " + (Get-Variable -Name Scope -Scope Private -ErrorAction SilentlyContinue).Value
    "Set Scope to : " + (Set-Variable -Name Scope -Scope Private -Value "end" -Option Private -PassThru).Value
}

Using the trap statement outside of the input processing methods (begin, process, end) causes unexpected token and/or not recognized term errors. A workaround seems to be to use the source or dot operator on the input processing method blocks to bring them into the same scope. I am not sure if this was intended as using this method does not allow continued execution.

trap {
    Write-Output "Block is: trap"
    "Scope is: " + (Get-Variable -Name Scope -Scope Private -ErrorAction SilentlyContinue).Value
    "Set Scope to : " + (Set-Variable -Name Scope -Scope Private -Value "trap" -Option Private -PassThru).Value
    continue
}

. {
    begin {
        Write-Output "Block is: begin"
        "Scope is: " + (Get-Variable -Name Scope -Scope Private -ErrorAction SilentlyContinue).Value
        "Set Scope to : " + (Set-Variable -Name Scope -Scope Private -Value "begin" -Option Private -PassThru).Value


    }

    process {
        Write-Output "Block is: process"
        "Scope is: " + (Get-Variable -Name Scope -Scope Private -ErrorAction SilentlyContinue).Value
        "Set Scope to : " + (Set-Variable -Name Scope -Scope Private -Value "process" -Option Private -PassThru).Value

        #throw "error"
    }

    end {
        Write-Output "Block is: end"
        "Scope is: " + (Get-Variable -Name Scope -Scope Private -ErrorAction SilentlyContinue).Value
        "Set Scope to : " + (Set-Variable -Name Scope -Scope Private -Value "end" -Option Private -PassThru).Value
    }
}

If it is intended that the trap statement is bound by script blocks, that should be documented as it not currently intuitive.

Expected behavior

Block is: begin
Scope is:
Set Scope to : begin
Block is: process
Scope is: begin
Set Scope to : process
Block is: trap
Scope is:
Set Scope to : trap
Block is: end
Scope is: process
Set Scope to : end

Actual behavior

Block is: begin
Scope is:
Set Scope to : begin
Block is: process
Scope is: begin
Set Scope to : process
Exception: \test-trap.ps1:21
Line |
  21 |      throw "error"
     |      ~~~~~~~~~~~~~
     | error

Error details

No response

Environment data

Name                           Value
----                           -----
PSVersion                      7.2.2
PSEdition                      Core
GitCommitId                    7.2.2
OS                             Microsoft Windows 10.0.22000
Platform                       Win32NT
PSCompatibleVersions           {1.0, 2.0, 3.0, 4.0…}
PSRemotingProtocolVersion      2.3
SerializationVersion           1.1.0.1
WSManStackVersion              3.0

Visuals

No response

[daxian-dbw]

... anywhere within a given scope ...

I think this is a doc issue. It should be within a given script block. The trap statement only covers statements within the same script block.

You need to put the trap in the same block (script block) where exception is thrown, or use try/catch in the same block.
If you don't attempt to continue execution from the exception, a new feature introduced in PowerShell 7.3 preview supports a new clean block for resource cleanup, which will act on exception thrown from any of the begin, process, or end blocks.

[daxian-dbw]

Opened the doc issue: MicrosoftDocs/PowerShell-Docs#8865

This issue has been marked as answered and has not had any activity for 1 day. It has been closed for housekeeping purposes.