Add SymbolMoniker helper

src/EditorFeatures/Core/SymbolMonikers/SymbolMoniker.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.
+
+#nullable enable
+
+using System;
+using VS.IntelliNav.Contracts;
+
+namespace Microsoft.CodeAnalysis.SymbolMonikers
+{
+    internal class SymbolMoniker : ISymbolMoniker
+    {
+        public string Scheme { get; }
+
+        public string Identifier { get; }
+
+        public IPackageInformation? PackageInformation { get; }
+
+        public SymbolMoniker(string scheme, string identifier)
+        {
+            this.Scheme = scheme;
+            this.Identifier = identifier;
+        }
+
+        public static ISymbolMoniker? TryCreate(ISymbol symbol)
+        {
+            // This uses the existing format that earlier prototypes of the Roslyn LSIF tool implemented; a different format may make more sense long term, but changing the
+            // moniker makes it difficult for other systems that have older LSIF indexes to the connect the two indexes together.
+
+            // Skip all local things that cannot escape outside of a single file: downstream consumers simply treat this as meaning a references/definition result
+            // doesn't need to be stitched together across files or multiple projects or repositories.
+            if (symbol.Kind == SymbolKind.Local ||
+                symbol.Kind == SymbolKind.RangeVariable ||
+                symbol.Kind == SymbolKind.Label ||
+                symbol.Kind == SymbolKind.Alias)
+            {
+                return null;
+            }
+
+            // Skip built in-operators. We could pick some sort of moniker for these, but I doubt anybody really needs to search for all uses of
+            // + in the world's projects at once.
+            if (symbol is IMethodSymbol method && method.MethodKind == MethodKind.BuiltinOperator)
+            {
+                return null;
+            }
+
+            // TODO: some symbols for things some things in crefs don't have a ContainingAssembly. We'll skip those for now but do
+            // want those to work.
+            if (symbol.Kind != SymbolKind.Namespace && symbol.ContainingAssembly == null)
+            {
+                return null;
+            }
+
+            // Namespaces are special: they're just a name that exists in the ether between compilations
+            if (symbol.Kind == SymbolKind.Namespace)
+            {
+                return new SymbolMoniker(WellKnownSymbolMonikerSchemes.DotnetNamespace, symbol.ToDisplayString());
+            }
+
+            var symbolMoniker = symbol.ContainingAssembly.Name + "#";
+
+            if (symbol.Kind == SymbolKind.Parameter)
+            {
+                symbolMoniker += GetRequiredDocumentationCommentId(symbol.ContainingSymbol) + "#" + symbol.Name;
+            }
+            else
+            {
+                symbolMoniker += GetRequiredDocumentationCommentId(symbol);
+            }
+
+            return new SymbolMoniker(WellKnownSymbolMonikerSchemes.DotnetXmlDoc, symbolMoniker);
+
+            static string GetRequiredDocumentationCommentId(ISymbol symbol)
+            {
+                var documentationCommentId = symbol.GetDocumentationCommentId();
+
+                if (documentationCommentId == null)
+                {
+                    throw new Exception($"Unable to get documentation comment ID for {symbol.ToDisplayString()}");
+                }
+
+                return documentationCommentId;
+            }
+        }
+    }
+}

src/EditorFeatures/Core/SymbolMonikers/WellKnownSymbolMonikerSchemes.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.
+
+#nullable enable
+
+
+namespace Microsoft.CodeAnalysis.SymbolMonikers
+{
+    internal static class WellKnownSymbolMonikerSchemes
+    {
+        public static string DotnetNamespace = "dotnet-namespace";
+        public static string DotnetXmlDoc = "dotnet-xml-doc";
+    }
+}