Don't map completion items to function (#47412)

src/Features/LanguageServer/Protocol/Extensions/ProtocolConversions.cs

@@ -24,6 +24,8 @@ namespace Microsoft.CodeAnalysis.LanguageServer
 {
     internal static class ProtocolConversions
     {
+        // NOTE: While the spec allows it, don't use Function and Method, as both VS and VS Code display them the same way
+        // which can confuse users
         public static readonly Dictionary<string, LSP.CompletionItemKind> RoslynTagToCompletionItemKind = new Dictionary<string, LSP.CompletionItemKind>()
         {
             { WellKnownTags.Public, LSP.CompletionItemKind.Keyword },
@@ -36,7 +38,7 @@ internal static class ProtocolConversions
             { WellKnownTags.Assembly, LSP.CompletionItemKind.File },
             { WellKnownTags.Class, LSP.CompletionItemKind.Class },
             { WellKnownTags.Constant, LSP.CompletionItemKind.Constant },
-            { WellKnownTags.Delegate, LSP.CompletionItemKind.Function },
+            { WellKnownTags.Delegate, LSP.CompletionItemKind.Method },
             { WellKnownTags.Enum, LSP.CompletionItemKind.Enum },
             { WellKnownTags.EnumMember, LSP.CompletionItemKind.EnumMember },
             { WellKnownTags.Event, LSP.CompletionItemKind.Event },
@@ -326,7 +328,6 @@ public static LSP.SymbolKind GlyphToSymbolKind(Glyph glyph)
                 case Glyph.DelegateProtected:
                 case Glyph.DelegatePrivate:
                 case Glyph.DelegateInternal:
-                    return LSP.SymbolKind.Function;
                 case Glyph.ExtensionMethodPublic:
                 case Glyph.ExtensionMethodProtected:
                 case Glyph.ExtensionMethodPrivate:
@@ -355,9 +356,8 @@ public static Glyph CompletionItemKindToGlyph(LSP.CompletionItemKind kind)
                     return Glyph.None;
                 case LSP.CompletionItemKind.Method:
                 case LSP.CompletionItemKind.Constructor:
+                case LSP.CompletionItemKind.Function:    // We don't use Function, but map it just in case. It has the same icon as Method in VS and VS Code
                     return Glyph.MethodPublic;
-                case LSP.CompletionItemKind.Function:
-                    return Glyph.DelegatePublic;
                 case LSP.CompletionItemKind.Field:
                     return Glyph.FieldPublic;
                 case LSP.CompletionItemKind.Variable:

src/Features/LanguageServer/ProtocolUnitTests/ProtocolConversionsTests.cs

+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+
+using System.Linq;
+using Microsoft.VisualStudio.LanguageServer.Protocol;
+using Xunit;
+
+namespace Microsoft.CodeAnalysis.LanguageServer.UnitTests
+{
+    public class ProtocolConversionsTests
+    {
+        [Fact]
+        public void CompletionItemKind_DontUseMethodAndFunction()
+        {
+            var map = ProtocolConversions.RoslynTagToCompletionItemKind;
+
+            var containsMethod = map.Values.Any(c => c == CompletionItemKind.Method);
+            var containsFunction = map.Values.Any(c => c == CompletionItemKind.Function);
+
+            Assert.False(containsFunction && containsMethod, "Don't use Method and Function completion item kinds as it causes user confusion.");
+        }
+    }
+}