WIP: Evaluate variables on hover

If their value is available (either because its been set in the session
manually, or the script has been executed or is being debugged) we can
return it on the hover.

We should ask if we actually want to do this, and if so, how we want to
format it.

src/PowerShellEditorServices/Services/PowerShell/Handlers/EvaluateHandler.cs

@@ -1,6 +1,7 @@
 // Copyright (c) Microsoft Corporation.
 // Licensed under the MIT License.
 
+using System.Collections.Generic;
 using System.Management.Automation;
 using System.Threading;
 using System.Threading.Tasks;
@@ -22,9 +23,9 @@ internal class EvaluateHandler : IEvaluateHandler
         public async Task<EvaluateResponseBody> Handle(EvaluateRequestArguments request, CancellationToken cancellationToken)
         {
             // This API is mostly used for F8 execution so it requires the foreground.
-            await _executionService.ExecutePSCommandAsync(
+            IReadOnlyList<PSObject> results = await _executionService.ExecutePSCommandAsync<PSObject>(
                 new PSCommand().AddScript(request.Expression),
-                CancellationToken.None,
+                cancellationToken,
                 new PowerShellExecutionOptions
                 {
                     RequiresForeground = true,
@@ -34,10 +35,9 @@ await _executionService.ExecutePSCommandAsync(
                     ThrowOnError = false,
                 }).ConfigureAwait(false);
 
-            // TODO: Should we return a more informative result?
             return new EvaluateResponseBody
             {
-                Result = "",
+                Result = string.Join(System.Environment.NewLine, results),
                 VariablesReference = 0
             };
         }

src/PowerShellEditorServices/Services/TextDocument/Handlers/HoverHandler.cs

@@ -1,11 +1,15 @@
 // Copyright (c) Microsoft Corporation.
 // Licensed under the MIT License.
 
+using System;
 using System.Collections.Generic;
+using System.Management.Automation;
 using System.Threading;
 using System.Threading.Tasks;
 using Microsoft.Extensions.Logging;
 using Microsoft.PowerShell.EditorServices.Services;
+using Microsoft.PowerShell.EditorServices.Services.PowerShell;
+using Microsoft.PowerShell.EditorServices.Services.PowerShell.Execution;
 using Microsoft.PowerShell.EditorServices.Services.Symbols;
 using Microsoft.PowerShell.EditorServices.Services.TextDocument;
 using Microsoft.PowerShell.EditorServices.Utility;
@@ -18,15 +22,18 @@ namespace Microsoft.PowerShell.EditorServices.Handlers
     internal class PsesHoverHandler : HoverHandlerBase
     {
         private readonly ILogger _logger;
+        private readonly IInternalPowerShellExecutionService _executionService;
         private readonly SymbolsService _symbolsService;
         private readonly WorkspaceService _workspaceService;
 
         public PsesHoverHandler(
             ILoggerFactory factory,
+            IInternalPowerShellExecutionService executionService,
             SymbolsService symbolsService,
             WorkspaceService workspaceService)
         {
             _logger = factory.CreateLogger<PsesHoverHandler>();
+            _executionService = executionService;
             _symbolsService = symbolsService;
             _workspaceService = workspaceService;
         }
@@ -63,6 +70,21 @@ await _symbolsService.FindSymbolDetailsAtLocationAsync(
                 new MarkedString("PowerShell", symbolDetails.SymbolReference.Name)
             };
 
+            // If we're looking at a variable, try to get its value.
+            if (symbolDetails.SymbolReference.Type == SymbolType.Variable)
+            {
+                PSCommand command = new PSCommand().AddScript($"[System.Diagnostics.DebuggerHidden()]param() {symbolDetails.SymbolReference.Name}");
+                IReadOnlyList<PSObject> results = await _executionService.ExecutePSCommandAsync<PSObject>(
+                    command,
+                    cancellationToken,
+                    new PowerShellExecutionOptions { ThrowOnError = false }).ConfigureAwait(false);
+
+                if (results != null)
+                {
+                    symbolInfo.Add(new MarkedString("PowerShell", string.Join(Environment.NewLine, results)));
+                }
+            }
+
             if (!string.IsNullOrEmpty(symbolDetails.Documentation))
             {
                 symbolInfo.Add(new MarkedString("markdown", symbolDetails.Documentation));