Write custom full prompt each time it is displayed

This change fixes an issue where the user's custom prompt function is
only written out fully (including any Write-Host or Write-Output
behavior) the first time the prompt appears after a command is executed.
This is because the return value of the prompt function was being cached
and re-printed each time the user hit Enter without running a new
command.

Resolves PowerShell/vscode-powershell#774.

Author: daviwil

src/PowerShellEditorServices/Console/ConsoleService.cs

@@ -13,6 +13,7 @@ namespace Microsoft.PowerShell.EditorServices.Console
     using Microsoft.PowerShell.EditorServices.Session;
     using System;
     using System.Globalization;
+    using System.Linq;
     using System.Management.Automation;
     using System.Security;
 
@@ -218,9 +219,24 @@ public async Task<SecureString> ReadSecureLine(CancellationToken cancellationTok
 
         #region Private Methods
 
-        private void WritePromptStringToHost()
+        private async Task WritePromptStringToHost()
         {
-            string promptString = this.powerShellContext.PromptString;
+            PSCommand promptCommand = new PSCommand().AddScript("prompt");
+
+            string promptString =
+                (await this.powerShellContext.ExecuteCommand<object>(promptCommand, false, false))
+                    .OfType<string>()
+                    .FirstOrDefault() ?? "PS> ";
+
+            // Add the [DBG] prefix if we're stopped in the debugger
+            if (this.powerShellContext.IsDebuggerStopped)
+            {
+                promptString =
+                    string.Format(
+                        CultureInfo.InvariantCulture,
+                        "[DBG]: {0}",
+                        promptString);
+            }
 
             // Update the stored prompt string if the session is remote
             if (this.powerShellContext.CurrentRunspace.Location == RunspaceLocation.Remote)
@@ -295,7 +311,7 @@ private async Task StartReplLoop(CancellationToken cancellationToken)
             {
                 string commandString = null;
 
-                this.WritePromptStringToHost();
+                await this.WritePromptStringToHost();
 
                 try
                 {

src/PowerShellEditorServices/Session/PowerShellContext.cs

@@ -103,14 +103,6 @@ public RunspaceDetails CurrentRunspace
             private set;
         }
 
-        /// <summary>
-        /// Gets the prompt string for the current runspace.
-        /// </summary>
-        public string PromptString
-        {
-            get { return this.mostRecentSessionDetails.PromptString; }
-        }
-
         #endregion
 
         #region Constructors

src/PowerShellEditorServices/Session/SessionDetails.cs

@@ -15,11 +15,6 @@ namespace Microsoft.PowerShell.EditorServices.Session
     /// </summary>
     public class SessionDetails
     {
-        /// <summary>
-        /// Gets the current prompt string.
-        /// </summary>
-        public string PromptString { get; internal set; }
-
         /// <summary>
         /// Gets the process ID of the current process.
         /// </summary>
@@ -47,7 +42,6 @@ public SessionDetails(PSObject detailsObject)
 
             Hashtable innerHashtable = detailsObject.BaseObject as Hashtable;
 
-            this.PromptString = innerHashtable["prompt"] as string ?? "PS> ";
             this.ProcessId = (int)innerHashtable["processId"] as int?;
             this.ComputerName = innerHashtable["computerName"] as string;
             this.InstanceId = innerHashtable["instanceId"] as Guid?;
@@ -62,7 +56,7 @@ public static PSCommand GetDetailsCommand()
         {
             PSCommand infoCommand = new PSCommand();
             infoCommand.AddScript(
-                "@{ 'prompt' = prompt; 'computerName' = $env:ComputerName; 'processId' = $PID; 'instanceId' = $host.InstanceId }");
+                "@{ 'computerName' = $env:ComputerName; 'processId' = $PID; 'instanceId' = $host.InstanceId }");
 
             return infoCommand;
         }