Add variance results to tracing, capture variance verification on annotated type params (#49712)

* Add variance results to tracing

* Tweak format, prohibit `results` on `E` events

src/compiler/checker.ts

@@ -20785,7 +20785,7 @@ namespace ts {
                     variances.push(variance);
                 }
                 links.variances = variances;
-                tracing?.pop();
+                tracing?.pop({ variances: variances.map(Debug.formatVariance) });
             }
             return links.variances;
         }
@@ -35055,12 +35055,14 @@ namespace ts {
                         error(node, Diagnostics.Variance_annotations_are_only_supported_in_type_aliases_for_object_function_constructor_and_mapped_types);
                     }
                     else if (modifiers === ModifierFlags.In || modifiers === ModifierFlags.Out) {
+                        tracing?.push(tracing.Phase.CheckTypes, "checkTypeParameterDeferred", { parent: getTypeId(getDeclaredTypeOfSymbol(symbol)), id: getTypeId(typeParameter) });
                         const source = createMarkerType(symbol, typeParameter, modifiers === ModifierFlags.Out ? markerSubTypeForCheck : markerSuperTypeForCheck);
                         const target = createMarkerType(symbol, typeParameter, modifiers === ModifierFlags.Out ? markerSuperTypeForCheck : markerSubTypeForCheck);
                         const saveVarianceTypeParameter = typeParameter;
                         varianceTypeParameter = typeParameter;
                         checkTypeAssignableTo(source, target, node, Diagnostics.Type_0_is_not_assignable_to_type_1_as_implied_by_variance_annotation);
                         varianceTypeParameter = saveVarianceTypeParameter;
+                        tracing?.pop();
                     }
                 }
             }

src/compiler/debug.ts

@@ -748,5 +748,22 @@ namespace ts {
             const deprecation = createDeprecation(options?.name ?? getFunctionName(func), options);
             return wrapFunction(deprecation, func);
         }
+
+        export function formatVariance(varianceFlags: VarianceFlags) {
+            const variance = varianceFlags & VarianceFlags.VarianceMask;
+            let result =
+                variance === VarianceFlags.Invariant ? "in out" :
+                variance === VarianceFlags.Bivariant ? "[bivariant]" :
+                variance === VarianceFlags.Contravariant ? "in" :
+                variance === VarianceFlags.Covariant ? "out" :
+                variance === VarianceFlags.Independent ? "[independent]" : "";
+            if (varianceFlags & VarianceFlags.Unmeasurable) {
+                result += " (unmeasurable)";
+            }
+            else if (varianceFlags & VarianceFlags.Unreliable) {
+                result += " (unreliable)";
+            }
+            return result;
+        }
     }
 }

src/compiler/tracing.ts

@@ -131,9 +131,9 @@ namespace ts { // eslint-disable-line one-namespace-per-file
             }
             eventStack.push({ phase, name, args, time: 1000 * timestamp(), separateBeginAndEnd });
         }
-        export function pop() {
+        export function pop(results?: Args) {
             Debug.assert(eventStack.length > 0);
-            writeStackEvent(eventStack.length - 1, 1000 * timestamp());
+            writeStackEvent(eventStack.length - 1, 1000 * timestamp(), results);
             eventStack.length--;
         }
         export function popAll() {
@@ -145,14 +145,15 @@ namespace ts { // eslint-disable-line one-namespace-per-file
         }
         // sample every 10ms
         const sampleInterval = 1000 * 10;
-        function writeStackEvent(index: number, endTime: number) {
+        function writeStackEvent(index: number, endTime: number, results?: Args) {
             const { phase, name, args, time, separateBeginAndEnd } = eventStack[index];
             if (separateBeginAndEnd) {
+                Debug.assert(!results, "`results` are not supported for events with `separateBeginAndEnd`");
                 writeEvent("E", phase, name, args, /*extras*/ undefined, endTime);
             }
             // test if [time,endTime) straddles a sampling point
             else if (sampleInterval - (time % sampleInterval) <= endTime - time) {
-                writeEvent("X", phase, name, args, `"dur":${endTime - time}`, time);
+                writeEvent("X", phase, name, { ...args, results }, `"dur":${endTime - time}`, time);
             }
         }