Add support for cref-type-parameters.

src/Workspaces/Core/Portable/SymbolKey/SymbolKey.BodyLevelSymbolKey.cs

@@ -4,7 +4,7 @@
 
 using System.Collections.Generic;
 using System.Threading;
-using Microsoft.CodeAnalysis.Text;
+using Microsoft.CodeAnalysis.Shared.Extensions;
 
 namespace Microsoft.CodeAnalysis
 {
@@ -34,13 +34,11 @@ public static void Create(ISymbol symbol, SymbolKeyWriter visitor)
                 // locals in VB can't be found using GetDeclaredSymbol.  For those, we store the actual local span and
                 // use GetSymbolInfo to find it.
                 var ordinal = GetOrdinal();
-                var span = symbol.Locations[0].SourceSpan;
 
                 visitor.WriteString(localName);
                 visitor.WriteSymbolKey(containingSymbol);
                 visitor.WriteInteger(ordinal);
-                visitor.WriteInteger(span.Start);
-                visitor.WriteInteger(span.Length);
+                visitor.WriteLocation(symbol.Locations[0]);
                 visitor.WriteInteger((int)kind);
 
                 return;
@@ -64,8 +62,7 @@ public static SymbolKeyResolution Resolve(SymbolKeyReader reader)
                 var localName = reader.ReadString();
                 var containingSymbolResolution = reader.ReadSymbolKey();
                 var ordinal = reader.ReadInteger();
-                var spanStart = reader.ReadInteger();
-                var spanLength = reader.ReadInteger();
+                var location = reader.ReadLocation();
                 var kind = (SymbolKind)reader.ReadInteger();
 
                 var containingSymbol = containingSymbolResolution.Symbol;
@@ -81,23 +78,9 @@ public static SymbolKeyResolution Resolve(SymbolKeyReader reader)
                     }
                     else
                     {
-                        var span = new TextSpan(spanStart, spanLength);
-                        foreach (var containerRef in containingSymbol.DeclaringSyntaxReferences)
-                        {
-                            var containerNode = containerRef.GetSyntax(cancellationToken);
-                            if (containerNode.Parent.Span.Contains(span))
-                            {
-                                var syntaxTree = containerRef.SyntaxTree;
-                                var node = syntaxTree.GetRoot(cancellationToken).FindNode(span, getInnermostNodeForTie: true);
-                                var semanticModel = reader.Compilation.GetSemanticModel(syntaxTree);
-                                var info = semanticModel.GetSymbolInfo(node, cancellationToken);
-                                if (info.Symbol != null)
-                                    return new SymbolKeyResolution(info.Symbol);
-
-                                if (info.CandidateSymbols.Length > 0)
-                                    return new SymbolKeyResolution(info.CandidateSymbols, info.CandidateReason);
-                            }
-                        }
+                        var resolution = reader.ResolveLocation(location);
+                        if (resolution != null)
+                            return resolution.Value;
                     }
                 }
 

src/Workspaces/Core/Portable/SymbolKey/SymbolKey.SymbolKeyReader.cs

@@ -9,6 +9,7 @@
 using System.Text;
 using System.Threading;
 using Microsoft.CodeAnalysis.PooledObjects;
+using Microsoft.CodeAnalysis.Shared.Extensions;
 using Microsoft.CodeAnalysis.Shared.Utilities;
 using Microsoft.CodeAnalysis.Text;
 using Roslyn.Utilities;
@@ -445,7 +446,7 @@ private SymbolKeyResolution ReadWorker(SymbolKeyType type)
             /// will either be the same as the original amount written, or <c>default</c> will be 
             /// returned. It will never be less or more.  <c>default</c> will be returned if any 
             /// elements could not be resolved to the requested <typeparamref name="TSymbol"/> type 
-            /// in the provided <see cref="Compilation"/>.
+            /// in the provided <see cref="SymbolKeyReader.Compilation"/>.
             /// 
             /// Callers should <see cref="IDisposable.Dispose"/> the instance returned.  No check is
             /// necessary if <c>default</c> was returned before calling <see cref="IDisposable.Dispose"/>
@@ -545,6 +546,23 @@ public Location ReadLocation()
                 return Location.None;
             }
 
+            public SymbolKeyResolution? ResolveLocation(Location location)
+            {
+                if (location.SourceTree != null)
+                {
+                    var node = location.FindNode(findInsideTrivia: true, getInnermostNodeForTie: true, CancellationToken);
+                    var semanticModel = Compilation.GetSemanticModel(location.SourceTree);
+                    var info = semanticModel.GetSymbolInfo(node, CancellationToken);
+                    if (info.Symbol != null)
+                        return new SymbolKeyResolution(info.Symbol);
+
+                    if (info.CandidateSymbols.Length > 0)
+                        return new SymbolKeyResolution(info.CandidateSymbols, info.CandidateReason);
+                }
+
+                return null;
+            }
+
             private IModuleSymbol GetModule(IEnumerable<IModuleSymbol> modules, string moduleName)
             {
                 foreach (var module in modules)

src/Workspaces/Core/Portable/SymbolKey/SymbolKey.TypeParameterSymbolKey.cs

@@ -12,28 +12,48 @@ private static class TypeParameterSymbolKey
         {
             public static void Create(ITypeParameterSymbol symbol, SymbolKeyWriter visitor)
             {
-                visitor.WriteString(symbol.MetadataName);
-                visitor.WriteSymbolKey(symbol.ContainingSymbol);
+                if (symbol.TypeParameterKind == TypeParameterKind.Cref)
+                {
+                    visitor.WriteBoolean(true);
+                    visitor.WriteLocation(symbol.Locations[0]);
+                }
+                else
+                {
+                    visitor.WriteBoolean(false);
+                    visitor.WriteString(symbol.MetadataName);
+                    visitor.WriteSymbolKey(symbol.ContainingSymbol);
+                }
             }
 
             public static SymbolKeyResolution Resolve(SymbolKeyReader reader)
             {
-                var metadataName = reader.ReadString();
-                var containingSymbolResolution = reader.ReadSymbolKey();
+                var isCref = reader.ReadBoolean();
 
-                using var result = PooledArrayBuilder<ITypeParameterSymbol>.GetInstance();
-                foreach (var containingSymbol in containingSymbolResolution)
+                if (isCref)
                 {
-                    foreach (var typeParam in containingSymbol.GetTypeParameters())
+                    var location = reader.ReadLocation();
+                    var resolution = reader.ResolveLocation(location);
+                    return resolution.GetValueOrDefault();
+                }
+                else
+                {
+                    var metadataName = reader.ReadString();
+                    var containingSymbolResolution = reader.ReadSymbolKey();
+
+                    using var result = PooledArrayBuilder<ITypeParameterSymbol>.GetInstance();
+                    foreach (var containingSymbol in containingSymbolResolution)
                     {
-                        if (typeParam.MetadataName == metadataName)
+                        foreach (var typeParam in containingSymbol.GetTypeParameters())
                         {
-                            result.AddIfNotNull(typeParam);
+                            if (typeParam.MetadataName == metadataName)
+                            {
+                                result.AddIfNotNull(typeParam);
+                            }
                         }
                     }
-                }
 
-                return CreateResolution(result);
+                    return CreateResolution(result);
+                }
             }
         }
     }

src/Workspaces/Core/Portable/Workspace/Solution/SolutionState.SymbolToProjectId.cs

@@ -87,6 +87,15 @@ internal partial class SolutionState
                     }
                 }
             }
+            else if (symbol.IsKind(SymbolKind.TypeParameter, out ITypeParameterSymbol? typeParameter) &&
+                     typeParameter.TypeParameterKind == TypeParameterKind.Cref)
+            {
+                // Cref type parameters don't belong to any containing symbol.  But we can map them to a doc/project
+                // using the declaring syntax of the type parameter itself.
+                var tree = typeParameter.Locations[0].SourceTree;
+                var doc = this.GetDocumentState(tree, projectId: null);
+                return doc?.Id.ProjectId;
+            }
 
             return null;
         }