Temporarily mitigate intermittent IntelliSense slowness

This change mitigates seemingly intermittent IntelliSense slowness by
preventing Get-Command and Get-Help from being called on cmdlets from
the PowerShellGet and PackageManagement modules.  Something in the
PackageManagement module is causing completions to be returned at 10x
delay when that module is loaded.  If the module is removed from the
session, completions go back to their normal duration.

By avoiding calling Get-Command on these cmdlets, we avoid loading
PackageManagement when the user types a string like `Get-P` which
incidentally happens to make VS Code see the `Get-Package` cmdlet and
try to resolve its details.

This fix is temporary and will be removed in the future once
OneGet/oneget#275 is fixed.

Related to PowerShell/vscode-powershell#647

Author: daviwil

src/PowerShellEditorServices.Protocol/Server/LanguageServer.cs

@@ -758,10 +758,13 @@ await CommandHelpers.GetCommandInfo(
                         completionItem.Label,
                         this.editorSession.PowerShellContext);
 
-                completionItem.Documentation =
-                    await CommandHelpers.GetCommandSynopsis(
-                        commandInfo,
-                        this.editorSession.PowerShellContext);
+                if (commandInfo != null)
+                {
+                    completionItem.Documentation =
+                        await CommandHelpers.GetCommandSynopsis(
+                            commandInfo,
+                            this.editorSession.PowerShellContext);
+                }
             }
 
             // Send back the updated CompletionItem

src/PowerShellEditorServices/Language/CommandHelpers.cs

@@ -3,6 +3,8 @@
 // Licensed under the MIT license. See LICENSE file in the project root for full license information.
 //
 
+using Microsoft.PowerShell.EditorServices.Utility;
+using System.Collections.Generic;
 using System.Linq;
 using System.Management.Automation;
 using System.Threading.Tasks;
@@ -14,6 +16,20 @@ namespace Microsoft.PowerShell.EditorServices
     /// </summary>
     public class CommandHelpers
     {
+        private static HashSet<string> NounBlackList =
+            new HashSet<string>
+            {
+                "Module",
+                "Script",
+                "Package",
+                "PackageProvider",
+                "PackageSource",
+                "InstalledModule",
+                "InstalledScript",
+                "ScriptFileInfo",
+                "PSRepository"
+            };
+
         /// <summary>
         /// Gets the CommandInfo instance for a command with a particular name.
         /// </summary>
@@ -24,6 +40,18 @@ public static async Task<CommandInfo> GetCommandInfo(
             string commandName,
             PowerShellContext powerShellContext)
         {
+            Validate.IsNotNull(nameof(commandName), commandName);
+
+            // Make sure the command's noun isn't blacklisted.  This is
+            // currently necessary to make sure that Get-Command doesn't
+            // load PackageManagement or PowerShellGet because they cause
+            // a major slowdown in IntelliSense.
+            var commandParts = commandName.Split('-');
+            if (commandParts.Length == 2 && NounBlackList.Contains(commandParts[1]))
+            {
+                return null;
+            }
+
             PSCommand command = new PSCommand();
             command.AddCommand(@"Microsoft.PowerShell.Core\Get-Command");
             command.AddArgument(commandName);