Fixes #1028 - Code Coverage for proxy functions/steppablePipelines (updated to v5.0.3)

[leojackson]

1. General summary of the pull request

Note: This PR contains the same bug fix as #1494, but is based on the v5.0 branch instead of master.

---

Pester generates all breakpoints using a combination of line number and column number. PowerShell does not trigger breakpoints on the proxy function constructs described in #1028 when initiated using both line and column number, but it does when using line number only. This appears to be a bug within PowerShell itself, as the behavior can be replicated outside of Pester like so:

# Create a new proxy function for Write-Output in a file in the current directory
$ProxyMetadata = New-Object System.Management.Automation.CommandMetaData (Get-Command Write-Output)
@"
Function Write-FancyTestOutput {
$([System.Management.Automation.ProxyCommand]::Create($ProxyMetadata))
}
"@ | Out-File $PWD\Write-FancyTestOutput.ps1

# Get AST for the new function
$ast = [System.Management.Automation.Language.Parser]::ParseFile( `
    "$PWD\Write-FancyTestOutput.ps1", `
    [ref]$null, `
    [ref]$null `
)

# Initialize line number var
$LineNumber = 0

# Use FindAll to loop through all commands, look for the
# '& $wrappedCmd @PSBoundParameters' command, and add a
# breakpoint at line & column for that command -- this is
# what Pester currently does
$ast.FindAll( `
    {$args[0] -is [System.Management.Automation.Language.CommandBaseAst]}, `
    $true `
) | Where-Object {
    $_.Extent.Text -like '*& $wrappedCmd @PSBoundParameters*'
} | ForEach-Object {
    If($LineNumber -le 0) {
        $LineNumber = $_.Extent.StartLineNumber
    }
    Set-PSBreakpoint -Script "$PWD\Write-FancyTestOutput.ps1" `
                     -Action { } `
                     -Line $_.Extent.StartLineNumber `
                     -Column $_.Extent.StartColumnNumber
}

. $PWD\Write-FancyTestOutput.ps1
Write-FancyTestOutput -InputObject "Hello"   # will not trigger any breakpoints

# Add another breakpoint with no column specified for the same line
If($LineNumber -gt 0) {
    Set-PSBreakpoint -Script "$PWD\Write-FancyTestOutput.ps1" `
                     -Action { } `
                     -Line $LineNumber
}

Write-FancyTestOutput -InputObject "Hello again"   # Triggers the last breakpoint
Get-PSBreakpoint | fl

...which results in this output:

Id       : 0
Script   : C:\Temp\Write-FancyTestOutput.ps1
Line     : 22
Column   : 22
Enabled  : True
HitCount : 0
Action   :

Id       : 1
Script   : C:\Temp\Write-FancyTestOutput.ps1
Line     : 22
Column   : 23
Enabled  : True
HitCount : 0
Action   :

Id       : 2
Script   : C:\Temp\Write-FancyTestOutput.ps1
Line     : 22
Column   : 0
Enabled  : True
HitCount : 1
Action   :

Rather than trying to rewrite Pester to create breakpoints without column specifications, this PR includes proxy functions using steppable pipelines in the IsIgnoredCommand private function. I feel this is appropriate because in proxy command situations, the steppable pipeline constituents are already covered by breakpoints.

It does this be validating two criteria:

• The extent text of the command matches '^{?& \$wrappedCmd @PSBoundParameters ?}?$', which matches the specific constructs created when auto-generating a proxy command using [System.Management.Automation.ProxyCommand]::Create().
• The topmost parent of the command is like '*$steppablePipeline.Begin($PSCmdlet)*$steppablePipeline.Process($_)*$steppablePipeline.End()*', which matches when all three of the steppable pipeline steps have been defined in the function or file where this proxy command is defined.

Since there is no out-of-the-box mechanism to recursively iterate through nested AST objects to get to the topmost parent, this PR also includes a new private function, Get-AstTopParent, that does exactly that.

Fix #1028

[nohwnd]

Thank you!