PipeScript

0.1.4

Transpilers/Explicit.psx.ps1

<#
.Synopsis
    Makes Output from a PowerShell function Explicit.
.Description
    Makes a PowerShell function explicitly output.

    All statements will be assigned to $null, unless they explicitly use Write-Output or echo.

    If Write-Output or echo is used, the command will be replaced for more effecient output.
.EXAMPLE
    Invoke-PipeScript {
        [explicit()]
        param()
        "This Will Not Output"
        Write-Output "This Will Output"
    }
.EXAMPLE
    {
        [explicit]{
            1,2,3,4
            echo "Output"
        }
    } | .>PipeScript
#>
[OutputType([ScriptBlock])]
param(
# The ScriptBlock that will be transpiled.
[Parameter(Mandatory,ValueFromPipeline)]
[ScriptBlock]
$ScriptBlock
)

process {
    # Search the ScriptBlock for
    $pipelines = $ScriptBlock.Ast.FindAll({
        param($ast)
        # all pipelines
        if ($ast -isnot [System.Management.Automation.Language.PipelineAst]) {
            return $false
        }
        # (as long as they are not the child or grandchild of Command, Assignment, or Return statements)
        $ignoreTypes = 'CommandAst', 'AssignmentStatementAst', 'ReturnStatementAst'
        $pipelineParent = $ast.Parent
        $pipelineGrandParent = $ast.Parent.Parent
        if ($pipelineParent -and $pipelineParent.GetType().Name -in $ignoreTypes) {
            return $false
        }
        if ($pipelineGrandParent -and $pipelineGrandParent.GetType().Name -in $ignoreTypes) {
            return $false
        }        
        return $true
    }, $false)

    $astReplacements = [Ordered]@{}
    foreach ($pipeline in $pipelines) {        
        $nullify = $pipeline.PipelineElements[-1] -isnot [Management.Automation.Language.CommandAst]
        if (-not $nullify) {
            $cmdName = $pipeline.PipelineElements[-1].CommandElements[0].Value
            $isOutputCmdName = '^(?>Out|Write|Show|Format)'
            $resolvedAlias = $ExecutionContext.SessionState.InvokeCommand.GetCommand($cmdName, 'Alias')
            $nullify = 
                $cmdName -notmatch $isOutputCmdName -and
                $resolvedAlias.Definition -notmatch $isOutputCmdName
        
            $isWriteOutput = $cmdName -in 'Write-Output', 'echo', 'write'
            if ($isWriteOutput) {
                if ($pipeline.PipelineElements.Count -gt 1) {                    
                    $strPipeline = "$pipeline"
                    $restOfPipeline = $strPipeline.Substring(0,
                        $strPipeline.Length - $pipeline.PipelineElements[-1].ToString().Length)
                    $astReplacements[$pipeline] = [ScriptBlock]::Create($restOfPipeline.TrimEnd().TrimEnd('|'))
                } else {
                    $ce = $pipeline.PipelineElements[0].CommandElements
                    $astReplacements[$pipeline] = [ScriptBlock]::Create($ce[1..($ce.Count - 1)] -join ' ')
                }
                continue
            }
        }

        if ($nullify) {
            $astReplacements[$pipeline] =  [ScriptBlock]::Create("`$null = $pipeline")
        }
    }

    Update-PipeScript -ScriptBlock $ScriptBlock -AstReplacement $astReplacements    
}