Enable transcription of native commands on non-Windows (PowerShell#4871)

Transcription was relying on reading the screen buffer to record output from native commands.
This resulted in an unhandled exception calling an unimplemented API on non-Windows.
The fix is to use redirected output/error if reading the screen buffer is not supported.
We check whether screen scraping is supported or not only when the application is running standalone.

Author: SteveL-MSFT

src/System.Management.Automation/engine/NativeCommandProcessor.cs

@@ -185,6 +185,8 @@ internal NativeCommandProcessor(ApplicationInfo applicationInfo, ExecutionContex
 
             //Create input writer for providing input to the process.
             _inputWriter = new ProcessInputWriter(Command);
+
+            _isTranscribing = this.Command.Context.EngineHostInterface.UI.IsTranscribing;
         }
 
         /// <summary>
@@ -373,8 +375,8 @@ internal override void ProcessRecord()
         /// </summary>
         private BlockingCollection<ProcessOutputObject> _nativeProcessOutputQueue;
 
-        private bool _scrapeHostOutput;
-
+        private static bool? s_supportScreenScrape = null;
+        private bool _isTranscribing;
         private Host.Coordinates _startPosition;
 
         /// <summary>
@@ -398,11 +400,13 @@ private void InitNativeProcess()
             // redirecting anything. This is a bit tricky as we always run redirected so
             // we have to see if the redirection is actually being done at the topmost level or not.
 
-            //Calculate if input and output are redirected.
+            // Calculate if input and output are redirected.
             bool redirectOutput;
             bool redirectError;
             bool redirectInput;
 
+            _startPosition = new Host.Coordinates();
+
             CalculateIORedirection(out redirectOutput, out redirectError, out redirectInput);
 
             // Find out if it's the only command in the pipeline.
@@ -416,9 +420,6 @@ private void InitNativeProcess()
                 throw new PipelineStoppedException();
             }
 
-            _startPosition = new Host.Coordinates();
-            _scrapeHostOutput = false;
-
             Exception exceptionToRethrow = null;
             try
             {
@@ -432,19 +433,10 @@ private void InitNativeProcess()
 
                     // Also, store the Raw UI coordinates so that we can scrape the screen after
                     // if we are transcribing.
-                    try
+                    if (_isTranscribing && (true == s_supportScreenScrape))
                     {
-                        if (this.Command.Context.EngineHostInterface.UI.IsTranscribing)
-                        {
-                            _scrapeHostOutput = true;
-                            _startPosition = this.Command.Context.EngineHostInterface.UI.RawUI.CursorPosition;
-                            _startPosition.X = 0;
-                        }
-                    }
-                    catch (Host.HostException)
-                    {
-                        // The host doesn't support scraping via its RawUI interface
-                        _scrapeHostOutput = false;
+                        _startPosition = this.Command.Context.EngineHostInterface.UI.RawUI.CursorPosition;
+                        _startPosition.X = 0;
                     }
                 }
 
@@ -697,9 +689,8 @@ internal override void Complete()
                     ConsumeAvailableNativeProcessOutput(blocking: true);
                     _nativeProcess.WaitForExit();
 
-                    // Capture screen output if we are transcribing
-                    if (this.Command.Context.EngineHostInterface.UI.IsTranscribing &&
-                        _scrapeHostOutput)
+                    // Capture screen output if we are transcribing and running stand alone
+                    if (_isTranscribing && (true == s_supportScreenScrape) && _runStandAlone)
                     {
                         Host.Coordinates endPosition = this.Command.Context.EngineHostInterface.UI.RawUI.CursorPosition;
                         endPosition.X = this.Command.Context.EngineHostInterface.UI.RawUI.BufferSize.Width - 1;
@@ -1287,6 +1278,33 @@ private void CalculateIORedirection(out bool redirectOutput, out bool redirectEr
             }
 
             _runStandAlone = !redirectInput && !redirectOutput && !redirectError;
+
+            if (_runStandAlone)
+            {
+                if (null == s_supportScreenScrape)
+                {
+                    try
+                    {
+                        _startPosition = this.Command.Context.EngineHostInterface.UI.RawUI.CursorPosition;
+                        Host.BufferCell[,] bufferContents = this.Command.Context.EngineHostInterface.UI.RawUI.GetBufferContents(
+                            new Host.Rectangle(_startPosition, _startPosition));
+                        s_supportScreenScrape = true;
+                    }
+                    catch (Exception)
+                    {
+                        s_supportScreenScrape = false;
+                    }
+                }
+
+                // if screen scraping isn't supported, we enable redirection so that the output is still transcribed
+                // as redirected output is always transcribed
+                if (_isTranscribing && (false == s_supportScreenScrape))
+                {
+                    redirectOutput = true;
+                    redirectError = true;
+                    _runStandAlone = false;
+                }
+            }
         }
 
         private bool ValidateExtension(string path)

test/powershell/Modules/Microsoft.Powershell.Host/Start-Transcript.Tests.ps1

@@ -107,20 +107,19 @@ Describe "Start-Transcript, Stop-Transcript tests" -tags "CI" {
         ValidateTranscription -scriptToExecute $script -outputFilePath $null -expectedError $expectedError
     }
     It "Transcription should remain active if other runspace in the host get closed" {
-        try{
+        try {
             $ps = [powershell]::Create()
             $ps.addscript("Start-Transcript -path $transcriptFilePath").Invoke()
             $ps.addscript('$rs = [system.management.automation.runspaces.runspacefactory]::CreateRunspace()').Invoke()
             $ps.addscript('$rs.open()').Invoke()
             $ps.addscript('$rs.Dispose()').Invoke()
             $ps.addscript('Write-Host "After Dispose"').Invoke()
             $ps.addscript("Stop-Transcript").Invoke()
-            } finally {
-                if ($null -ne $ps) {
-                    $ps.Dispose()
-                }
+        } finally {
+            if ($null -ne $ps) {
+                $ps.Dispose()
             }
-
+        }
 
         Test-Path $transcriptFilePath | Should be $true
         $transcriptFilePath | Should contain "After Dispose"
@@ -136,4 +135,15 @@ Describe "Start-Transcript, Stop-Transcript tests" -tags "CI" {
         $transcriptFilePath | Should contain "PowerShell transcript end"
     }
 
-}
+    It "Transcription should record native command output" {
+        $script = {
+            Start-Transcript -Path $transcriptFilePath
+            hostname
+            Stop-Transcript }
+        & $script
+        Test-Path $transcriptFilePath | Should be $true
+
+        $machineName = [System.Environment]::MachineName
+        $transcriptFilePath | Should contain $machineName
+    }
+}

test/powershell/engine/Job/Jobs.Tests.ps1

@@ -17,6 +17,21 @@ Describe 'Basic Job Tests' -Tags 'CI' {
         Receive-Job $job -wait | should be 1
     }
 
+    It "Create job with native command" {
+        try {
+            $nativeJob = Start-job { powershell -c 1+1 }
+            $nativeJob | Wait-Job
+            $nativeJob.State | Should BeExactly "Completed"
+            $nativeJob.HasMoreData | Should Be $true
+            Receive-Job $nativeJob | Should BeExactly 2
+            Remove-Job $nativeJob
+            { Get-Job $nativeJob -ErrorAction Stop } | ShouldBeErrorId "JobWithSpecifiedNameNotFound,Microsoft.PowerShell.Commands.GetJobCommand"
+        }
+        finally {
+            Remove-Job $nativeJob -Force -ErrorAction SilentlyContinue
+        }
+    }
+
     AfterAll {
         Remove-Job $job -Force
     }