Make more explicit the fact that MarkerPayload is nullable

src/profile-logic/marker-data.js

@@ -496,9 +496,9 @@ export function deriveMarkersFromRawMarkerTable(
   // In the case of separate markers for the start and end of an interval,
   // merge the payloads together, with the end data overriding the start.
   function mergeIntervalData(
-    startData: MarkerPayload,
-    endData: MarkerPayload
-  ): MarkerPayload {
+    startData: MarkerPayload | null,
+    endData: MarkerPayload | null
+  ): MarkerPayload | null {
     if (!startData && !endData) {
       return null;
     }

src/profile-logic/process-profile.js

@@ -661,13 +661,16 @@ function _processStackTable(
  * synchronous stack. Otherwise, if it happened before, it was an async stack, and is
  * most likely some event that happened in the past that triggered the marker.
  */
-function _convertStackToCause(data: any): any {
+function _convertStackToCause(data: MarkerPayload_Gecko) {
   if ('stack' in data && data.stack && data.stack.samples.data.length > 0) {
     const { stack, ...newData } = data;
     const stackIndex = stack.samples.data[0][stack.samples.schema.stack];
     const time = stack.samples.data[0][stack.samples.schema.time];
     if (stackIndex !== null) {
-      newData.cause = { tid: stack.tid, time, stack: stackIndex };
+      return {
+        ...newData,
+        cause: { tid: stack.tid, time, stack: stackIndex },
+      };
     }
     return newData;
   }
@@ -679,7 +682,7 @@ function _convertStackToCause(data: any): any {
  * from a gecko payload.
  */
 function _convertPayloadStackToIndex(
-  data: MarkerPayload_Gecko
+  data: MarkerPayload_Gecko | null
 ): IndexIntoStackTable | null {
   if (!data) {
     return null;
@@ -714,7 +717,7 @@ function _processMarkers(geckoMarkers: GeckoMarkerStruct): {|
   let hasMemoryAddresses;
 
   for (let markerIndex = 0; markerIndex < geckoMarkers.length; markerIndex++) {
-    const geckoPayload: MarkerPayload_Gecko = geckoMarkers.data[markerIndex];
+    const geckoPayload = geckoMarkers.data[markerIndex];
 
     if (geckoPayload) {
       switch (geckoPayload.type) {
@@ -844,8 +847,8 @@ function convertPhaseTimes(
  * the GC information.
  */
 function _processMarkerPayload(
-  geckoPayload: MarkerPayload_Gecko
-): MarkerPayload {
+  geckoPayload: MarkerPayload_Gecko | null
+): MarkerPayload | null {
   if (!geckoPayload) {
     return null;
   }
@@ -904,10 +907,14 @@ function _processMarkerPayload(
       }
     }
     default:
-      // Coerce the payload into a MarkerPayload. This doesn't really provide
-      // any more type safety, but it shows the intent of going from an object
-      // without much type safety, to a specific type definition.
-      return (payload: MarkerPayload);
+      // `payload` is currently typed as the result of _convertStackToCause, which
+      // is MarkerPayload_Gecko where `stack` has been replaced with `cause`. This
+      // should be reasonably close to `MarkerPayload`, but Flow doesn't work well
+      // with our MarkerPayload type. So we're coerce this return value to `any`
+      // here, and then to `MarkerPayload` as the return value for this function.
+      // This doesn't provide type safety but it shows the intent of going from an
+      // object without much type safety, to a specific type definition.
+      return (payload: any);
   }
 }
 

src/profile-logic/profile-data.js

@@ -3091,8 +3091,8 @@ export function replaceStackReferences(
 
   // Markers
   function replaceStackReferenceInMarkerPayload(
-    oldData: MarkerPayload
-  ): MarkerPayload {
+    oldData: MarkerPayload | null
+  ): MarkerPayload | null {
     if (oldData && 'cause' in oldData && oldData.cause) {
       // Replace the cause with the right stack index.
       // Use (...: any) because our current version of Flow has trouble with

src/test/fixtures/profiles/gecko-profile.js

@@ -336,7 +336,7 @@ type TestDefinedGeckoMarker = {|
   +endTime: Milliseconds | null,
   +phase: MarkerPhase,
   +category?: IndexIntoCategoryList,
-  +data?: MarkerPayload_Gecko,
+  +data?: MarkerPayload_Gecko | null,
 |};
 
 function _createGeckoThreadWithMarkers(

src/test/fixtures/profiles/processed-profile.js

@@ -75,7 +75,7 @@ export type TestDefinedMarkers = Array<
       MarkerName,
       MarkerTime, // start time
       MarkerTime | null, // end time
-      MarkerPayload | MockPayload
+      MarkerPayload | MockPayload | null
     ]
 >;
 
@@ -86,7 +86,7 @@ export type TestDefinedRawMarker = {|
   +endTime: Milliseconds | null,
   +phase: MarkerPhase,
   +category?: IndexIntoCategoryList,
-  +data?: MarkerPayload,
+  +data?: MarkerPayload | null,
 |};
 
 export type TestDefinedJsTracerEvent = [
@@ -131,7 +131,7 @@ export function addMarkersToThreadWithCorrespondingSamples(
     const startTime = tuple[1];
     // Flow doesn't support variadic tuple types.
     const maybeEndTime = (tuple: any)[2] || null;
-    const payload: MarkerPayload = (tuple: any)[3] || null;
+    const payload: MarkerPayload | null = (tuple: any)[3] || null;
 
     markersTable.name.push(stringTable.indexForString(name));
     if (maybeEndTime === null) {

src/types/gecko-profile.js

@@ -44,7 +44,7 @@ export type GeckoMarkerTuple = [
   Milliseconds | null,
   MarkerPhase,
   IndexIntoCategoryList,
-  MarkerPayload_Gecko
+  MarkerPayload_Gecko | null
 ];
 
 export type GeckoMarkers = {
@@ -70,7 +70,7 @@ export type GeckoMarkerStruct = {|
   startTime: Milliseconds[],
   endTime: Milliseconds[],
   phase: MarkerPhase[],
-  data: MarkerPayload_Gecko[],
+  data: Array<MarkerPayload_Gecko | null>,
   category: IndexIntoCategoryList[],
   length: number,
 |};

src/types/markers.js

@@ -766,8 +766,7 @@ export type MarkerPayload =
   | MediaSampleMarkerPayload
   | JankPayload
   | BrowsertimeMarkerPayload
-  | NoPayloadUserData
-  | null;
+  | NoPayloadUserData;
 
 export type MarkerPayload_Gecko =
   | GPUMarkerPayload
@@ -795,6 +794,4 @@ export type MarkerPayload_Gecko =
   | $ReplaceCauseWithStack<FileIoPayload>
   | $ReplaceCauseWithStack<PaintProfilerMarkerTracing>
   | $ReplaceCauseWithStack<StyleMarkerPayload>
-  | $ReplaceCauseWithStack<TextMarkerPayload>
-  // Payloads can be null.
-  | null;
+  | $ReplaceCauseWithStack<TextMarkerPayload>;

src/types/profile-derived.js

@@ -197,7 +197,7 @@ export type Marker = {|
   name: string,
   category: IndexIntoCategoryList,
   threadId: Tid | null,
-  data: MarkerPayload,
+  data: MarkerPayload | null,
   incomplete?: boolean,
 |};
 

src/types/profile.js

@@ -253,7 +253,7 @@ export type ProfilerMarkerPayload = {
  * it into a structured marker.
  */
 export type RawMarkerTable = {|
-  data: MarkerPayload[],
+  data: Array<MarkerPayload | null>,
   name: IndexIntoStringTable[],
   startTime: Array<number | null>,
   endTime: Array<number | null>,