Merge pull request #19539 from CyrusNajmabadi/gotodefPerf

Fix perf regression in gotodef.

src/EditorFeatures/Core/FindUsages/ClassifiedSpansAndHighlightSpan.cs

@@ -43,7 +43,8 @@ public static async Task<ClassifiedSpansAndHighlightSpan> ClassifyAsync(
             // If the document span is providing us with the classified spans up front, then we
             // can just use that.  Otherwise, go back and actually classify the text for the line
             // the document span is on.
-            if (documentSpan.Properties.TryGetValue(Key, out var value))
+            if (documentSpan.Properties != null &&
+                documentSpan.Properties.TryGetValue(Key, out var value))
             {
                 return (ClassifiedSpansAndHighlightSpan)value;
             }

src/EditorFeatures/Core/FindUsages/IDefinitionsAndReferencesFactory.cs

@@ -12,6 +12,7 @@
 using Microsoft.CodeAnalysis.Host;
 using Microsoft.CodeAnalysis.Host.Mef;
 using Microsoft.CodeAnalysis.Shared.Extensions;
+using Roslyn.Utilities;
 
 namespace Microsoft.CodeAnalysis.Editor.FindUsages
 {
@@ -47,7 +48,7 @@ public static DefinitionItem ToNonClassifiedDefinitionItem(
             // to compute the classified spans for the locations of the definition.  So it's totally 
             // fine to pass in CancellationToken.None and block on the result.
             return ToDefinitionItemAsync(definition, solution, includeHiddenLocations,
-                includeClassifiedSpans: false, cancellationToken: CancellationToken.None).Result;
+                includeClassifiedSpans: false, cancellationToken: CancellationToken.None).WaitAndGetResult_CanCallOnBackground(CancellationToken.None);
         }
 
         public static Task<DefinitionItem> ToClassifiedDefinitionItemAsync(

src/EditorFeatures/Core/GoToDefinition/GoToDefinitionHelpers.cs

@@ -61,8 +61,27 @@ public static bool TryGoToDefinition(
             }
 
             var definitions = ArrayBuilder<DefinitionItem>.GetInstance();
-            var definitionItem = symbol.ToClassifiedDefinitionItemAsync(
-                solution, includeHiddenLocations: true, cancellationToken: cancellationToken).WaitAndGetResult(cancellationToken);
+
+            // Going to a symbol may end up actually showing the symbol in the Find-Usages window.
+            // This happens when there is more than one location for the symbol (i.e. for partial
+            // symbols) and we don't know the best place to take you to.
+            //
+            // The FindUsages window supports showing the classified text for an item.  It does this
+            // in two ways.  Either the item can pass along its classified text (and the window will
+            // defer to that), or the item will have no classified text, and the window will compute
+            // it in the BG.
+            //
+            // Passing along the classified information is valuable for OOP scenarios where we want
+            // all that expensive computation done on the OOP side and not in the VS side.
+            // 
+            // However, Go To Definition is all in-process, and is also synchronous.  So we do not
+            // want to fetch the classifications here.  It slows down the command and leads to a 
+            // measurable delay in our perf tests.
+            // 
+            // So, if we only have a single location to go to, this does no unnecessary work.  And,
+            // if we do have multiple locations to show, it will just be done in the BG, unblocking
+            // this command thread so it can return the user faster.
+            var definitionItem = symbol.ToNonClassifiedDefinitionItem(solution, includeHiddenLocations: true);
 
             if (thirdPartyNavigationAllowed)
             {