Add functionality to allow a Show-Command like panel in VS Code (#697)

* Return PowerShell Commands
Return all commands but aliases. We're returning the same as show-command

Author: corbob

src/PowerShellEditorServices.Protocol/LanguageServer/GetCommandRequest.cs

@@ -0,0 +1,34 @@
+//
+// Copyright (c) Microsoft. All rights reserved.
+// Licensed under the MIT license. See LICENSE file in the project root for full license information.
+//
+
+using Microsoft.PowerShell.EditorServices.Protocol.MessageProtocol;
+using System.Collections.Generic;
+using System.Management.Automation;
+
+namespace Microsoft.PowerShell.EditorServices.Protocol.LanguageServer
+{
+    /// <summary>
+    /// Describes the request to get the details for PowerShell Commands from the current session.
+    /// </summary>
+        public class GetCommandRequest
+    {
+        public static readonly
+            RequestType<string, object, object, object> Type =
+            RequestType<string, object, object, object>.Create("powerShell/getCommand");
+    }
+
+    /// <summary>
+    /// Describes the message to get the details for a single PowerShell Command
+    /// from the current session
+    /// </summary>
+    public class PSCommandMessage
+    {
+        public string Name { get; set; }
+        public string ModuleName { get; set; }
+        public string DefaultParameterSet { get; set; }
+        public Dictionary<string, ParameterMetadata> Parameters { get; set; }
+        public System.Collections.ObjectModel.ReadOnlyCollection<CommandParameterSetInfo> ParameterSets { get; set; }
+    }
+}

src/PowerShellEditorServices.Protocol/Server/LanguageServer.cs

@@ -13,6 +13,7 @@
 using Newtonsoft.Json.Linq;
 using System;
 using System.Collections.Generic;
+using System.Diagnostics;
 using System.IO;
 using System.Linq;
 using System.Management.Automation;
@@ -138,6 +139,7 @@ public void Start()
             this.messageHandlers.SetRequestHandler(ShowHelpRequest.Type, this.HandleShowHelpRequest);
 
             this.messageHandlers.SetRequestHandler(ExpandAliasRequest.Type, this.HandleExpandAliasRequest);
+            this.messageHandlers.SetRequestHandler(GetCommandRequest.Type, this.HandleGetCommandRequestAsync);
 
             this.messageHandlers.SetRequestHandler(FindModuleRequest.Type, this.HandleFindModuleRequest);
             this.messageHandlers.SetRequestHandler(InstallModuleRequest.Type, this.HandleInstallModuleRequest);
@@ -525,6 +527,48 @@ function __Expand-Alias {
             await requestContext.SendResult(result.First().ToString());
         }
 
+        private async Task HandleGetCommandRequestAsync(
+            string param,
+            RequestContext<object> requestContext)
+        {
+            PSCommand psCommand = new PSCommand();
+            if (!string.IsNullOrEmpty(param))
+            {    
+                psCommand.AddCommand("Microsoft.PowerShell.Core\\Get-Command").AddArgument(param);
+            }
+            else
+            {
+                // Executes the following:
+                // Get-Command -CommandType Function,Cmdlet,ExternalScript | Select-Object -Property Name,ModuleName | Sort-Object -Property Name
+                psCommand
+                    .AddCommand("Microsoft.PowerShell.Core\\Get-Command")
+                        .AddParameter("CommandType", new[]{"Function", "Cmdlet", "ExternalScript"})
+                    .AddCommand("Microsoft.PowerShell.Utility\\Select-Object")
+                        .AddParameter("Property", new[]{"Name", "ModuleName"})
+                    .AddCommand("Microsoft.PowerShell.Utility\\Sort-Object")
+                        .AddParameter("Property", "Name");
+            }
+            IEnumerable<PSObject> result = await this.editorSession.PowerShellContext.ExecuteCommand<PSObject>(psCommand);
+            var commandList = new List<PSCommandMessage>();
+
+            if (result != null)
+            {
+                foreach (dynamic command in result)
+                {
+                    commandList.Add(new PSCommandMessage
+                    {
+                        Name = command.Name,
+                        ModuleName = command.ModuleName,
+                        Parameters = command.Parameters,
+                        ParameterSets = command.ParameterSets,
+                        DefaultParameterSet = command.DefaultParameterSet
+                    });
+                }
+            }
+
+            await requestContext.SendResult(commandList);
+        }
+
         private async Task HandleFindModuleRequest(
             object param,
             RequestContext<object> requestContext)