Initial Attempt

Author: JustinGrote

src/PowerShellEditorServices/Server/PsesLanguageServer.cs

@@ -112,6 +112,7 @@ public async Task StartAsync()
                     .WithHandler<PsesCompletionHandler>(
                         new JsonRpcHandlerOptions() { RequestProcessType = RequestProcessType.Serial })
                     .WithHandler<PsesHoverHandler>()
+                    .WithHandler<PsesInlayHandler>()
                     .WithHandler<PsesSignatureHelpHandler>()
                     .WithHandler<PsesDefinitionHandler>()
                     .WithHandler<TemplateHandlers>()

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

@@ -0,0 +1,76 @@
+// Copyright (c) Microsoft Corporation.
+// Licensed under the MIT License.
+
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Threading;
+using System.Threading.Tasks;
+using Microsoft.Extensions.Logging;
+using Microsoft.PowerShell.EditorServices.Services;
+using Microsoft.PowerShell.EditorServices.Services.Symbols;
+using Microsoft.PowerShell.EditorServices.Services.TextDocument;
+using Microsoft.PowerShell.EditorServices.Utility;
+using OmniSharp.Extensions.LanguageServer.Protocol.Client.Capabilities;
+using OmniSharp.Extensions.LanguageServer.Protocol.Document;
+using OmniSharp.Extensions.LanguageServer.Protocol.Models;
+
+namespace Microsoft.PowerShell.EditorServices.Handlers;
+
+/// <summary>
+/// Resolves PowerShell types and parameters as inlay hints for the LSP client. See: https://microsoft.github.io/language-server-protocol/specifications/lsp/3.17/specification/#textDocument_inlayHints
+/// </summary>
+internal class PsesInlayHandler(
+    ILoggerFactory loggerFactory,
+    SymbolsService symbolsService,
+    WorkspaceService workspaceService
+) : InlayHintsHandlerBase
+{
+    private readonly ILogger logger = loggerFactory.CreateLogger<PsesInlayHandler>();
+
+    /// <summary>
+    /// Expresses the capabilities of our Inlay Hints handler to the LSP
+    /// </summary>
+    protected override InlayHintRegistrationOptions CreateRegistrationOptions(InlayHintClientCapabilities capability, ClientCapabilities clientCapabilities) => new()
+    {
+        DocumentSelector = LspUtils.PowerShellDocumentSelector,
+        WorkDoneProgress = false, //TODO: Report progress for large documents
+        ResolveProvider = false //TODO: Add a resolve Provider for detailed inlay information
+    };
+
+    public override async Task<InlayHint> Handle(InlayHint request, CancellationToken cancellationToken) => throw new NotImplementedException();
+
+    public override async Task<InlayHintContainer> Handle(InlayHintParams request, CancellationToken cancellationToken)
+    {
+        if (cancellationToken.IsCancellationRequested)
+        {
+            logger.LogDebug("InlayHint request canceled for file: {Uri}", request.TextDocument.Uri);
+            return null;
+        }
+
+        // TODO: Limit search to request.range
+        ScriptFile scriptFile = workspaceService.GetFile(request.TextDocument.Uri);
+
+        IEnumerable<SymbolReference> symbolReferences =
+            symbolsService.FindSymbolsInFile(scriptFile);
+
+        if (symbolReferences is null)
+        {
+            return null;
+        }
+
+        IEnumerable<InlayHint> inlayHints =
+            from s in symbolReferences
+            where s.Type == SymbolType.Variable | s.Type == SymbolType.Parameter
+            select new InlayHint
+            {
+                Kind = InlayHintKind.Type,
+                Position = new Position(
+                    s.ScriptRegion.StartLineNumber - 1,
+                    s.ScriptRegion.StartColumnNumber - 1),
+                Label = s.Type.ToString()
+            };
+
+        return new InlayHintContainer(inlayHints);
+    }
+}