PipeScript Module: Handling CommandNotFound (Fixes #281)

Author: James Brundage

PipeScript.ps1.psm1

@@ -19,4 +19,87 @@ $MyModule = $MyInvocation.MyCommand.ScriptBlock.Module
 $aliasList +=
     [GetExports("Alias")]$MyModule
 
-Export-ModuleMember -Function * -Alias $aliasList
+Export-ModuleMember -Function * -Alias $aliasList
+
+$global:ExecutionContext.SessionState.InvokeCommand.CommandNotFoundAction = {
+    param($sender, $eventArgs)
+
+    # Rather than be the only thing that can handle command not found, we start by broadcasting an event.
+    New-Event -SourceIdentifier "PowerShell.CommandNotFound"  -MessageData $notFoundArgs -Sender $global:ExecutionContext -EventArguments $notFoundArgs
+    
+    # Then, we do a bit of callstack peeking
+    $callstack = @(Get-PSCallStack)
+    $callstackPeek = $callstack[-1]
+    # When peeking in on a dynamic script block, the offsets may lie.
+    $column = [Math]::Max($callstackPeek.InvocationInfo.OffsetInLine, 1)
+    $line   = [Math]::Max($callstackPeek.InvocationInfo.ScriptLineNumber, 1)
+    $callingScriptBlock = $callstackPeek.InvocationInfo.MyCommand.ScriptBlock
+    # Now find all of the AST elements at this location.
+    $astFound  = @($callingScriptBlock.Ast.FindAll({
+        param($ast)
+        $ast.Extent.StartLineNumber -eq $line -and
+        $ast.Extent.StartColumnNumber -eq $column
+    }, $true))
+    if (-not $script:LastCommandNotFoundScript) {
+        $script:LastCommandNotFoundScript = $callingScriptBlock
+    } elseif ($script:LastCommandNotFoundScript -eq $callingScriptBlock) {
+        return
+    } else {
+        $script:LastCommandNotFoundScript = $callingScriptBlock
+    }
+
+    if (-not $callingScriptBlock) {
+        return
+    }
+
+    
+    $transpiledScriptBlock = 
+        try {
+            $callingScriptBlock.Transpile()
+        } catch {
+            Write-Error $_
+            return
+        }
+    if ($transpiledScriptBlock -and 
+        ($transpiledScriptBlock.ToString().Length -ne $callingScriptBlock.ToString().Length)) {
+        
+        $endStatements = $transpiledScriptBlock.Ast.EndBlock.Statements
+        $FirstExpression = 
+            if ($endStatements -and (
+                $endStatements[0] -is 
+                    [Management.Automation.Language.PipelineAst]
+                ) -and (                    
+                $endStatements[0].PipelineElements[0] -is 
+                    [Management.Automation.Language.CommandExpressionAst]
+                )
+            ) {
+                $endStatements[0].PipelineElements[0].Expression
+            } else { $null }
+            
+        if ($astFound -and 
+            $astFound[-1].Parent -is [Management.Automation.Language.AssignmentStatementAst] -and
+            (
+                $FirstExpression -is [Management.Automation.Language.BinaryExpressionAst] -or
+                $FirstExpression -is [Management.Automation.Language.ParenExpressionAst]
+            )
+        ) {
+            Write-Error "
+Will not interactively transpile {$callingScriptBlock} ( because it would overwrite $($astFound[-1].Parent.Left.Extent) )"
+            return
+        }
+
+        if ($astFound -and 
+            $astFound[-1].Parent -is [Management.Automation.Language.AssignmentStatementAst] -and
+            $endStatements -and 
+            $endStatements[0] -is [Management.Automation.Language.AssignmentStatementAst] -and 
+            $astFound[-1].Parent.Left.ToString() -eq $endStatements[0].Left.ToString()) {
+            $eventArgs.CommandScriptBlock = [ScriptBlock]::Create($endStatements[0].Right.ToString())
+            $eventArgs.StopSearch = $true
+        } else {
+            $eventArgs.CommandScriptBlock = $transpiledScriptBlock
+            $eventArgs.StopSearch = $true
+        }                            
+    }
+
+    return    
+}