Added default TabExpansion2 implementation so PSES works out of the box in a constrained runspace

Author: dkattan

src/PowerShellEditorServices.Hosting/EditorServicesLoader.cs

@@ -13,6 +13,7 @@
 using SMA = System.Management.Automation;
 using System.Management.Automation;
 using System.Management.Automation.Runspaces;
+using System.Linq;
 
 #if CoreCLR
 using System.Runtime.Loader;
@@ -257,9 +258,15 @@ private void UpdatePSModulePath()
             }
 
             string psModulePath = Environment.GetEnvironmentVariable("PSModulePath").TrimEnd(Path.PathSeparator);
+            string[] psModulePaths = psModulePath.Split(Path.PathSeparator);
+            if (psModulePaths.Any(a => a == _hostConfig.BundledModulePath))
+            {
+                _logger.Log(PsesLogLevel.Verbose, $"PSModulePath already contains '{_hostConfig.BundledModulePath}'");
+                return;
+            }
+            
             psModulePath = $"{psModulePath}{Path.PathSeparator}{_hostConfig.BundledModulePath}";
             Environment.SetEnvironmentVariable("PSModulePath", psModulePath);
-
             _logger.Log(PsesLogLevel.Verbose, $"Updated PSModulePath to: '{psModulePath}'");
         }
 

src/PowerShellEditorServices/Services/PowerShellContext/PowerShellContextService.cs

@@ -84,7 +84,61 @@ static PowerShellContextService()
         private readonly Stack<RunspaceDetails> runspaceStack = new Stack<RunspaceDetails>();
 
         private int isCommandLoopRestarterSet;
+        /// <summary>
+        /// This is the default function to use for tab expansion.
+        /// </summary>
+        private static string tabExpansionFunctionText = @"
+<# Options include:
+     RelativeFilePaths - [bool]
+         Always resolve file paths using Resolve-Path -Relative.
+         The default is to use some heuristics to guess if relative or absolute is better.
+
+   To customize your own custom options, pass a hashtable to CompleteInput, e.g.
+         return [System.Management.Automation.CommandCompletion]::CompleteInput($inputScript, $cursorColumn,
+             @{ RelativeFilePaths=$false }
+#>
+
+[CmdletBinding(DefaultParameterSetName = 'ScriptInputSet')]
+Param(
+    [Parameter(ParameterSetName = 'ScriptInputSet', Mandatory = $true, Position = 0)]
+    [string] $inputScript,
+
+    [Parameter(ParameterSetName = 'ScriptInputSet', Position = 1)]
+    [int] $cursorColumn = $inputScript.Length,
 
+    [Parameter(ParameterSetName = 'AstInputSet', Mandatory = $true, Position = 0)]
+    [System.Management.Automation.Language.Ast] $ast,
+
+    [Parameter(ParameterSetName = 'AstInputSet', Mandatory = $true, Position = 1)]
+    [System.Management.Automation.Language.Token[]] $tokens,
+
+    [Parameter(ParameterSetName = 'AstInputSet', Mandatory = $true, Position = 2)]
+    [System.Management.Automation.Language.IScriptPosition] $positionOfCursor,
+
+    [Parameter(ParameterSetName = 'ScriptInputSet', Position = 2)]
+    [Parameter(ParameterSetName = 'AstInputSet', Position = 3)]
+    [Hashtable] $options = $null
+)
+
+End
+{
+    if ($psCmdlet.ParameterSetName -eq 'ScriptInputSet')
+    {
+        return [System.Management.Automation.CommandCompletion]::CompleteInput(
+            <#inputScript#>  $inputScript,
+            <#cursorColumn#> $cursorColumn,
+            <#options#>      $options)
+    }
+    else
+    {
+        return [System.Management.Automation.CommandCompletion]::CompleteInput(
+            <#ast#>              $ast,
+            <#tokens#>           $tokens,
+            <#positionOfCursor#> $positionOfCursor,
+            <#options#>          $options)
+    }
+}
+        ";
         #endregion
 
         #region Properties
@@ -216,8 +270,15 @@ public static PowerShellContextService Create(
             if (hostStartupInfo.InitialSessionState.LanguageMode != PSLanguageMode.FullLanguage)
             {
                 if(hostStartupInfo.AdditionalModules.Count > 0)
+                {
                     hostStartupInfo.InitialSessionState.ImportPSModule(hostStartupInfo.AdditionalModules as string[]);
-                hostStartupInfo.InitialSessionState.ImportPSModule(new string[] { s_commandsModulePath });
+                }
+
+                hostStartupInfo.InitialSessionState.ImportPSModule(new [] { s_commandsModulePath });
+                if(!hostStartupInfo.InitialSessionState.Commands.Any(a=> a.Name.ToLower() == "tabexpansion2"))
+                {
+                    hostStartupInfo.InitialSessionState.Commands.Add(new SessionStateFunctionEntry("TabExpansion2", tabExpansionFunctionText));
+                }
             }
             Runspace runspace = PowerShellContextService.CreateRunspace(psHost, hostStartupInfo.InitialSessionState);
             powerShellContext.Initialize(hostStartupInfo.ProfilePaths, runspace, true, hostUserInterface);