Enable completion of variables across scriptblock scopes

[MartinGC94]

PR Summary

Enables completion of variables assigned in other scriptblocks like:
ls | foreach -Begin {$MyVar = "Hello"} -Process {$MyV<Tab>}
Scriptblocks that are executed as commands with ampersand are explicitly excluded because variables assigned in those are not available outside the scope.

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[daxian-dbw]

The change enables completion on some commands that are not appliable to the assumption, such as Invoke-Command, New-Module, and Register-ArgumentCompleter.

Quick search in a default session shows the following cmdlets that have parameter with the type ScriptBlock, some of them do not run the script block in the calling scope. So, it's better to restrict when this completion should be enabled.

PS:1> gcm -ParameterType ([scriptblock])

CommandType     Name                                               Version    Source
-----------     ----                                               -------    ------
Cmdlet          ForEach-Object                                     7.2.11.500 Microsoft.PowerShell.Core
Cmdlet          Invoke-Command                                     7.2.11.500 Microsoft.PowerShell.Core
Cmdlet          Measure-Command                                    7.0.0.0    Microsoft.PowerShell.Utility
Cmdlet          New-Module                                         7.2.11.500 Microsoft.PowerShell.Core
Cmdlet          Register-ArgumentCompleter                         7.2.11.500 Microsoft.PowerShell.Core
Cmdlet          Register-EngineEvent                               7.0.0.0    Microsoft.PowerShell.Utility
Cmdlet          Register-ObjectEvent                               7.0.0.0    Microsoft.PowerShell.Utility
Cmdlet          Set-PSBreakpoint                                   7.0.0.0    Microsoft.PowerShell.Utility
Cmdlet          Set-PSReadLineKeyHandler                           2.3.1      PSReadLine
Cmdlet          Set-PSReadLineOption                               2.3.1      PSReadLine
Cmdlet          Start-Job                                          7.2.11.500 Microsoft.PowerShell.Core
Cmdlet          Trace-Command                                      7.0.0.0    Microsoft.PowerShell.Utility
Cmdlet          Where-Object                                       7.2.11.500 Microsoft.PowerShell.Core

[MartinGC94]

@daxian-dbw Good point. I've changed it to only work for dot sourced scriptblocks, and arguments to Foreach/Where-Object. What prompted this change was me writing a pester test and being annoyed that a var in BeforeAll was not completable. Can I add third party commands like "BeforeAll" and "BeforeEach" to the whitelist?

[daxian-dbw]

Can I add third party commands like "BeforeAll" and "BeforeEach" to the whitelist?

Sure, I think they should be in the whitelist. You are really solving a pain point here 👍

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Size       : +33 -3
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Total files changed: 2

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.cs : +24 -3
.ps1 : +9 -0

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[daxian-dbw]

LGTM

[ghost]

🎉v7.4.0-preview.4 has been released which incorporates this pull request.:tada:

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