Add screen reader support to PSReadLine (#4854)

Author: daxian-dbw

PSReadLine/Accessibility.cs

@@ -2,6 +2,7 @@
 Copyright (c) Microsoft Corporation.  All rights reserved.
 --********************************************************************/
 
+using System.Diagnostics;
 using System.Runtime.InteropServices;
 
 namespace Microsoft.PowerShell.Internal
@@ -10,14 +11,82 @@ internal class Accessibility
     {
         internal static bool IsScreenReaderActive()
         {
-            bool returnValue = false;
-
             if (RuntimeInformation.IsOSPlatform(OSPlatform.Windows))
             {
-                PlatformWindows.SystemParametersInfo(PlatformWindows.SPI_GETSCREENREADER, 0, ref returnValue, 0);
+                return IsAnyWindowsScreenReaderEnabled();
+            }
+
+            if (RuntimeInformation.IsOSPlatform(OSPlatform.OSX))
+            {
+                return IsVoiceOverEnabled();
+            }
+
+            // TODO: Support Linux per https://code.visualstudio.com/docs/configure/accessibility/accessibility
+            return false;
+        }
+
+        private static bool IsAnyWindowsScreenReaderEnabled()
+        {
+            // The supposedly official way to check for a screen reader on
+            // Windows is SystemParametersInfo(SPI_GETSCREENREADER, ...) but it
+            // doesn't detect the in-box Windows Narrator and is otherwise known
+            // to be problematic.
+            //
+            // Unfortunately, the alternative method used by Electron and
+            // Chromium, where the relevant screen reader libraries (modules)
+            // are checked for does not work in the context of PowerShell
+            // because it relies on those applications injecting themselves into
+            // the app. Which they do not because PowerShell is not a windowed
+            // app, so we're stuck using the known-to-be-buggy way.
+            bool spiScreenReader = false;
+            PlatformWindows.SystemParametersInfo(PlatformWindows.SPI_GETSCREENREADER, 0, ref spiScreenReader, 0);
+            if (spiScreenReader)
+            {
+                return true;
+            }
+
+            // At least we can correctly check for Windows Narrator using the
+            // NarratorRunning mutex. Windows Narrator is mostly not broken with
+            // PSReadLine, not in the way that NVDA and VoiceOver are.
+            if (PlatformWindows.IsMutexPresent("NarratorRunning"))
+            {
+                return true;
+            }
+
+            return false;
+        }
+
+        private static bool IsVoiceOverEnabled()
+        {
+            try
+            {
+                // Use the 'defaults' command to check if VoiceOver is enabled
+                // This checks the com.apple.universalaccess preference for voiceOverOnOffKey
+                ProcessStartInfo startInfo = new()
+                {
+                    FileName = "defaults",
+                    Arguments = "read com.apple.universalaccess voiceOverOnOffKey",
+                    UseShellExecute = false,
+                    RedirectStandardOutput = true,
+                    RedirectStandardError = true,
+                    CreateNoWindow = true
+                };
+
+                using Process process = Process.Start(startInfo);
+                process.WaitForExit(250);
+                if (process.HasExited && process.ExitCode == 0)
+                {
+                    string output = process.StandardOutput.ReadToEnd().Trim();
+                    // VoiceOver is enabled if the value is 1
+                    return output == "1";
+                }
+            }
+            catch
+            {
+                // If we can't determine the status, assume VoiceOver is not enabled
             }
 
-            return returnValue;
+            return false;
         }
     }
 }

PSReadLine/BasicEditing.cs

@@ -86,7 +86,7 @@ public static void CancelLine(ConsoleKeyInfo? key = null, object arg = null)
             _singleton._current = _singleton._buffer.Length;
 
             using var _ = _singleton._prediction.DisableScoped();
-            _singleton.ForceRender();
+            _singleton.Render(force: true);
 
             _singleton._console.Write("\x1b[91m^C\x1b[0m");
 
@@ -335,7 +335,7 @@ private bool AcceptLineImpl(bool validate)
 
             if (renderNeeded)
             {
-                ForceRender();
+                Render(force: true);
             }
 
             // Only run validation if we haven't before.  If we have and status line shows an error,

PSReadLine/Cmdlets.cs

@@ -15,6 +15,7 @@
 using System.Runtime.InteropServices;
 using System.Threading;
 using Microsoft.PowerShell.PSReadLine;
+using Microsoft.PowerShell.Internal;
 using AllowNull = System.Management.Automation.AllowNullAttribute;
 
 namespace Microsoft.PowerShell
@@ -150,11 +151,6 @@ public class PSConsoleReadLineOptions
 
         public const HistorySaveStyle DefaultHistorySaveStyle = HistorySaveStyle.SaveIncrementally;
 
-        /// <summary>
-        /// The predictive suggestion feature is disabled by default.
-        /// </summary>
-        public const PredictionSource DefaultPredictionSource = PredictionSource.None;
-
         public const PredictionViewStyle DefaultPredictionViewStyle = PredictionViewStyle.InlineView;
 
         /// <summary>
@@ -201,6 +197,7 @@ public PSConsoleReadLineOptions(string hostName, bool usingLegacyConsole)
         {
             ResetColors();
             EditMode = DefaultEditMode;
+            ScreenReaderModeEnabled = Accessibility.IsScreenReaderActive();
             ContinuationPrompt = DefaultContinuationPrompt;
             ContinuationPromptColor = Console.ForegroundColor;
             ExtraPromptLineCount = DefaultExtraPromptLineCount;
@@ -533,6 +530,8 @@ public object ListPredictionTooltipColor
 
         public bool TerminateOrphanedConsoleApps { get; set; }
 
+        public bool ScreenReaderModeEnabled { get; set; }
+
         internal string _defaultTokenColor;
         internal string _commentColor;
         internal string _keywordColor;
@@ -847,6 +846,14 @@ public SwitchParameter TerminateOrphanedConsoleApps
         }
         internal SwitchParameter? _terminateOrphanedConsoleApps;
 
+        [Parameter]
+        public SwitchParameter EnableScreenReaderMode
+        {
+            get => _enableScreenReaderMode.GetValueOrDefault();
+            set => _enableScreenReaderMode = value;
+        }
+        internal SwitchParameter? _enableScreenReaderMode;
+
         [ExcludeFromCodeCoverage]
         protected override void EndProcessing()
         {

PSReadLine/Options.cs

@@ -185,6 +185,10 @@ private void SetOptionsInternal(SetPSReadLineOption options)
                             nameof(Options.TerminateOrphanedConsoleApps)));
                 }
             }
+            if (options._enableScreenReaderMode.HasValue)
+            {
+                Options.ScreenReaderModeEnabled = options.EnableScreenReaderMode;
+            }
         }
 
         private void SetKeyHandlerInternal(string[] keys, Action<ConsoleKeyInfo?, object> handler, string briefDescription, string longDescription, ScriptBlock scriptBlock)

PSReadLine/PlatformWindows.cs

@@ -79,6 +79,21 @@ IntPtr templateFileWin32Handle
     [DllImport("kernel32.dll", CharSet = CharSet.Unicode, SetLastError = true)]
     internal static extern IntPtr GetStdHandle(uint handleId);
 
+    internal const int ERROR_ALREADY_EXISTS = 0xB7;
+
+    internal static bool IsMutexPresent(string name)
+    {
+        try
+        {
+            using var mutex = new System.Threading.Mutex(false, name);
+            return Marshal.GetLastWin32Error() == ERROR_ALREADY_EXISTS;
+        }
+        catch
+        {
+            return false;
+        }
+    }
+
     [DllImport("kernel32.dll", CharSet = CharSet.Unicode, SetLastError = true)]
     static extern bool SetConsoleCtrlHandler(BreakHandler handlerRoutine, bool add);