Support ConstrainedLanguage mode

module/PowerShellEditorServices/Commands/Public/Clear-Host.ps1

@@ -10,7 +10,9 @@ function Clear-Host {
     param()
 
     __clearhost
-    $psEditor.Window.Terminal.Clear()
+    if ($host.Runspace.LanguageMode -eq [System.Management.Automation.PSLanguageMode]::FullLanguage) {
+        $psEditor.Window.Terminal.Clear()
+    }
 }
 
 if (!$IsMacOS -or $IsLinux) {

src/PowerShellEditorServices.Hosting/Commands/StartEditorServicesCommand.cs

@@ -11,6 +11,7 @@
 using System.Management.Automation;
 using System.Reflection;
 using SMA = System.Management.Automation;
+using System.Management.Automation.Runspaces;
 using Microsoft.PowerShell.EditorServices.Hosting;
 using System.Globalization;
 using System.Collections;
@@ -358,6 +359,7 @@ private EditorServicesConfig CreateConfigObject()
                 AdditionalModules = AdditionalModules,
                 LanguageServiceTransport = GetLanguageServiceTransport(),
                 DebugServiceTransport = GetDebugServiceTransport(),
+                LanguageMode = Runspace.DefaultRunspace.SessionStateProxy.LanguageMode,
                 ProfilePaths = new ProfilePathConfig
                 {
                     AllUsersAllHosts = GetProfilePathFromProfileObject(profile, ProfileUserKind.AllUsers, ProfileHostKind.AllHosts),

src/PowerShellEditorServices.Hosting/Configuration/EditorServicesConfig.cs

@@ -4,6 +4,7 @@
 //
 
 using System.Collections.Generic;
+using System.Management.Automation;
 using System.Management.Automation.Host;
 
 namespace Microsoft.PowerShell.EditorServices.Hosting
@@ -111,6 +112,12 @@ public EditorServicesConfig(
         /// </summary>
         public ProfilePathConfig ProfilePaths { get; set; }
 
+        /// <summary>
+        /// The language mode inherited from the orginal PowerShell process.
+        /// This will be used when creating runspaces so that we honor the same language mode.
+        /// </summary>
+        public PSLanguageMode LanguageMode { get; internal set; }
+
         public string StartupBanner { get; set; } = @"
 
                   =====> PowerShell Integrated Console <=====

src/PowerShellEditorServices.Hosting/EditorServicesLoader.cs

@@ -190,8 +190,6 @@ public Task LoadAndRunEditorServicesAsync()
             // Make sure the .NET Framework version supports .NET Standard 2.0
             CheckNetFxVersion();
 #endif
-            // Ensure the language mode allows us to run
-            CheckLanguageMode();
 
             // Add the bundled modules to the PSModulePath
             UpdatePSModulePath();
@@ -250,19 +248,6 @@ private void CheckNetFxVersion()
         }
 #endif
 
-        /// <summary>
-        /// PSES currently does not work in Constrained Language Mode, because PSReadLine script invocations won't work in it.
-        /// Ideally we can find a better way so that PSES will work in CLM.
-        /// </summary>
-        private void CheckLanguageMode()
-        {
-            _logger.Log(PsesLogLevel.Diagnostic, "Checking that PSES is running in FullLanguage mode");
-            if (Runspace.DefaultRunspace.SessionStateProxy.LanguageMode != PSLanguageMode.FullLanguage)
-            {
-                throw new InvalidOperationException("Cannot start PowerShell Editor Services in Constrained Language Mode");
-            }
-        }
-
         private void UpdatePSModulePath()
         {
             if (string.IsNullOrEmpty(_hostConfig.BundledModulePath))
@@ -332,7 +317,7 @@ private string GetPSOutputEncoding()
         {
             using (var pwsh = SMA.PowerShell.Create())
             {
-                return pwsh.AddScript("$OutputEncoding.EncodingName").Invoke<string>()[0];
+                return pwsh.AddScript("$OutputEncoding.EncodingName", useLocalScope: true).Invoke<string>()[0];
             }
         }
 

src/PowerShellEditorServices.Hosting/Internal/EditorServicesRunner.cs

@@ -237,6 +237,7 @@ private HostStartupInfo CreateHostStartupInfo()
                 profilePaths,
                 _config.FeatureFlags,
                 _config.AdditionalModules,
+                _config.LanguageMode,
                 _config.LogPath,
                 (int)_config.LogLevel,
                 consoleReplEnabled: _config.ConsoleRepl != ConsoleReplKind.None,

src/PowerShellEditorServices/Hosting/HostStartupInfo.cs

@@ -5,6 +5,7 @@
 
 using System;
 using System.Collections.Generic;
+using System.Management.Automation;
 using System.Management.Automation.Host;
 
 namespace Microsoft.PowerShell.EditorServices.Hosting
@@ -89,6 +90,12 @@ public sealed class HostStartupInfo
         /// </summary>
         public string LogPath { get; }
 
+        /// <summary>
+        /// The language mode inherited from the orginal PowerShell process.
+        /// This will be used when creating runspaces so that we honor the same language mode.
+        /// </summary>
+        public PSLanguageMode LanguageMode { get; }
+
         /// <summary>
         /// The minimum log level of log events to be logged.
         /// </summary>
@@ -117,6 +124,7 @@ public sealed class HostStartupInfo
         /// <param name="currentUsersProfilePath">The path to the user specific profile.</param>
         /// <param name="featureFlags">Flags of features to enable.</param>
         /// <param name="additionalModules">Names or paths of additional modules to import.</param>
+        /// <param name="languageMode">The language mode inherited from the orginal PowerShell process. This will be used when creating runspaces so that we honor the same language mode.</param>
         /// <param name="logPath">The path to log to.</param>
         /// <param name="logLevel">The minimum log event level.</param>
         /// <param name="consoleReplEnabled">Enable console if true.</param>
@@ -129,6 +137,7 @@ public HostStartupInfo(
             ProfilePathInfo profilePaths,
             IReadOnlyList<string> featureFlags,
             IReadOnlyList<string> additionalModules,
+            PSLanguageMode languageMode,
             string logPath,
             int logLevel,
             bool consoleReplEnabled,
@@ -141,6 +150,7 @@ public HostStartupInfo(
             ProfilePaths = profilePaths;
             FeatureFlags = featureFlags ?? Array.Empty<string>();
             AdditionalModules = additionalModules ?? Array.Empty<string>();
+            LanguageMode = languageMode;
             LogPath = logPath;
             LogLevel = logLevel;
             ConsoleReplEnabled = consoleReplEnabled;

src/PowerShellEditorServices/Services/PowerShellContext/PowerShellContextService.cs

@@ -213,7 +213,7 @@ public static PowerShellContextService Create(
                     hostUserInterface,
                     logger);
 
-            Runspace initialRunspace = PowerShellContextService.CreateRunspace(psHost);
+            Runspace initialRunspace = PowerShellContextService.CreateRunspace(psHost, hostStartupInfo.LanguageMode);
             powerShellContext.Initialize(hostStartupInfo.ProfilePaths, initialRunspace, true, hostUserInterface);
 
             powerShellContext.ImportCommandsModuleAsync();
@@ -244,9 +244,7 @@ public static PowerShellContextService Create(
         /// </summary>
         /// <param name="hostDetails"></param>
         /// <param name="powerShellContext"></param>
-        /// <param name="hostUserInterface">
-        /// The EditorServicesPSHostUserInterface to use for this instance.
-        /// </param>
+        /// <param name="hostUserInterface">The EditorServicesPSHostUserInterface to use for this instance.</param>
         /// <param name="logger">An ILogger implementation to use for this instance.</param>
         /// <returns></returns>
         public static Runspace CreateRunspace(
@@ -260,15 +258,16 @@ public static Runspace CreateRunspace(
             var psHost = new EditorServicesPSHost(powerShellContext, hostDetails, hostUserInterface, logger);
             powerShellContext.ConsoleWriter = hostUserInterface;
             powerShellContext.ConsoleReader = hostUserInterface;
-            return CreateRunspace(psHost);
+            return CreateRunspace(psHost, hostDetails.LanguageMode);
         }
 
         /// <summary>
         ///
         /// </summary>
-        /// <param name="psHost"></param>
+        /// <param name="psHost">The PSHost that will be used for this Runspace.</param>
+        /// <param name="languageMode">The language mode inherited from the orginal PowerShell process. This will be used when creating runspaces so that we honor the same language mode.</param>
         /// <returns></returns>
-        public static Runspace CreateRunspace(PSHost psHost)
+        public static Runspace CreateRunspace(PSHost psHost, PSLanguageMode languageMode)
         {
             InitialSessionState initialSessionState;
             if (Environment.GetEnvironmentVariable("PSES_TEST_USE_CREATE_DEFAULT") == "1") {
@@ -277,6 +276,11 @@ public static Runspace CreateRunspace(PSHost psHost)
                 initialSessionState = InitialSessionState.CreateDefault2();
             }
 
+            // Create and initialize a new Runspace while honoring the LanguageMode of the original runspace
+            // that started PowerShell Editor Services. This is because the PowerShell Integrated Console
+            // should have the same LanguageMode of whatever is set by the system.
+            initialSessionState.LanguageMode = languageMode;
+
             Runspace runspace = RunspaceFactory.CreateRunspace(psHost, initialSessionState);
 
             // Windows PowerShell must be hosted in STA mode
@@ -410,6 +414,8 @@ public void Initialize(
 
             if (powerShellVersion.Major >= 5 &&
                 this.isPSReadLineEnabled &&
+                // TODO: Figure out why PSReadLine isn't working in ConstrainedLanguage mode.
+                initialRunspace.SessionStateProxy.LanguageMode == PSLanguageMode.FullLanguage &&
                 PSReadLinePromptContext.TryGetPSReadLineProxy(logger, initialRunspace, out PSReadLineProxy proxy))
             {
                 this.PromptContext = new PSReadLinePromptContext(
@@ -597,7 +603,7 @@ public async Task<IEnumerable<TResult>> ExecuteCommandAsync<TResult>(
             // cancelled prompt when it's called again.
             if (executionOptions.AddToHistory)
             {
-                this.PromptContext.AddToHistory(psCommand.Commands[0].CommandText);
+                this.PromptContext.AddToHistory(executionOptions.InputString ?? psCommand.Commands[0].CommandText);
             }
 
             bool hadErrors = false;
@@ -686,7 +692,7 @@ public async Task<IEnumerable<TResult>> ExecuteCommandAsync<TResult>(
                 if (executionOptions.WriteInputToHost)
                 {
                     this.WriteOutput(
-                        psCommand.Commands[0].CommandText,
+                        executionOptions.InputString ?? psCommand.Commands[0].CommandText,
                         includeNewLine: true);
                 }
 
@@ -1161,7 +1167,7 @@ internal static TResult ExecuteScriptAndGetItem<TResult>(string scriptToExecute,
             using (PowerShell pwsh = PowerShell.Create())
             {
                 pwsh.Runspace = runspace;
-                IEnumerable<TResult> results = pwsh.AddScript(scriptToExecute).Invoke<TResult>();
+                IEnumerable<TResult> results = pwsh.AddScript(scriptToExecute, useLocalScope: true).Invoke<TResult>();
                 return results.DefaultIfEmpty(defaultValue).First();
             }
         }

src/PowerShellEditorServices/Services/PowerShellContext/Session/Capabilities/DscBreakpointCapability.cs

@@ -121,14 +121,17 @@ public static DscBreakpointCapability CheckForCapability(
                         runspaceDetails.AddCapability(capability);
 
                         powerShell.Commands.Clear();
-                        powerShell.AddScript("Write-Host \"Gathering DSC resource paths, this may take a while...\"");
-                        powerShell.Invoke();
+                        powerShell
+                            .AddCommand("Microsoft.PowerShell.Utility\\Write-Host")
+                            .AddArgument("Gathering DSC resource paths, this may take a while...")
+                            .Invoke();
 
                         // Get the list of DSC resource paths
                         powerShell.Commands.Clear();
-                        powerShell.AddCommand("Get-DscResource");
-                        powerShell.AddCommand("Select-Object");
-                        powerShell.AddParameter("ExpandProperty", "ParentPath");
+                        powerShell
+                            .AddCommand("Get-DscResource")
+                            .AddCommand("Select-Object")
+                            .AddParameter("ExpandProperty", "ParentPath");
 
                         Collection<PSObject> resourcePaths = null;
 

src/PowerShellEditorServices/Services/PowerShellContext/Session/ExecutionOptions.cs

@@ -46,6 +46,18 @@ internal class ExecutionOptions
         /// </summary>
         public bool WriteInputToHost { get; set; }
 
+        /// <summary>
+        /// If this is set, we will use this string for history and writing to the host
+        /// instead of grabbing the command from the PSCommand.
+        /// </summary>
+        public string InputString { get; set; }
+
+        /// <summary>
+        /// If this is set, we will use this string for history and writing to the host
+        /// instead of grabbing the command from the PSCommand.
+        /// </summary>
+        public bool UseNewScope { get; set; }
+
         /// <summary>
         /// Gets or sets a value indicating whether the command to
         /// be executed is a console input prompt, such as the

src/PowerShellEditorServices/Services/PowerShellContext/Session/PSReadLinePromptContext.cs

@@ -91,7 +91,7 @@ internal static bool TryGetPSReadLineProxy(
             {
                 pwsh.Runspace = runspace;
                 var psReadLineType = pwsh
-                    .AddScript(ReadLineInitScript)
+                    .AddScript(ReadLineInitScript, useLocalScope: true)
                     .Invoke<Type>()
                     .FirstOrDefault();
 

src/PowerShellEditorServices/Services/PowerShellContext/Session/SessionDetails.cs

@@ -56,7 +56,8 @@ public static PSCommand GetDetailsCommand()
         {
             PSCommand infoCommand = new PSCommand();
             infoCommand.AddScript(
-                "@{ 'computerName' = if ([Environment]::MachineName) {[Environment]::MachineName}  else {'localhost'}; 'processId' = $PID; 'instanceId' = $host.InstanceId }");
+                "@{ 'computerName' = if ([Environment]::MachineName) {[Environment]::MachineName}  else {'localhost'}; 'processId' = $PID; 'instanceId' = $host.InstanceId }",
+                useLocalScope: true);
 
             return infoCommand;
         }

test/PowerShellEditorServices.Test/PowerShellContextFactory.cs

@@ -12,6 +12,7 @@
 using System;
 using System.Collections.Generic;
 using System.IO;
+using System.Management.Automation;
 using System.Threading;
 using System.Threading.Tasks;
 
@@ -45,6 +46,7 @@ public static PowerShellContextService Create(ILogger logger)
                 TestProfilePaths,
                 new List<string>(),
                 new List<string>(),
+                PSLanguageMode.FullLanguage,
                 null,
                 0,
                 consoleReplEnabled: false,