[DevTools] Compute environment names for the timeline (facebook#34892)

Stacked on facebook#34885.

This refactors the timeline to store not just an id but a complex object
for each step. This will later represent a group of boundaries.

Each timeline step is assigned an environment name. We pick the last
environment name (assumed to have resolved last) from the union of the
parent and child environment names. I.e. a child step is considered to
be blocked by the parent so if a child isn't blocked on any environment
name it still gets marked as the parent's environment name.

In a follow up, I'd like to reorder the document order timeline based on
environment names to favor loading everything in one environment before
the next.

Author: sebmarkbage

packages/react-devtools-shared/src/devtools/store.js

@@ -34,6 +34,7 @@ import {
   shallowDiffers,
   utfDecodeStringWithRanges,
   parseElementDisplayNameFromBackend,
+  unionOfTwoArrays,
 } from '../utils';
 import {localStorageGetItem, localStorageSetItem} from '../storage';
 import {__DEBUG__} from '../constants';
@@ -51,6 +52,7 @@ import type {
   ComponentFilter,
   ElementType,
   SuspenseNode,
+  SuspenseTimelineStep,
   Rect,
 } from 'react-devtools-shared/src/frontend/types';
 import type {
@@ -895,13 +897,10 @@ export default class Store extends EventEmitter<{
    */
   getSuspendableDocumentOrderSuspense(
     uniqueSuspendersOnly: boolean,
-  ): $ReadOnlyArray<SuspenseNode['id']> {
+  ): $ReadOnlyArray<SuspenseTimelineStep> {
+    const target: Array<SuspenseTimelineStep> = [];
     const roots = this.roots;
-    if (roots.length === 0) {
-      return [];
-    }
-
-    const list: SuspenseNode['id'][] = [];
+    let rootStep: null | SuspenseTimelineStep = null;
     for (let i = 0; i < roots.length; i++) {
       const rootID = roots[i];
       const root = this.getElementByID(rootID);
@@ -912,44 +911,76 @@ export default class Store extends EventEmitter<{
 
       const suspense = this.getSuspenseByID(rootID);
       if (suspense !== null) {
-        if (list.length === 0) {
-          // start with an arbitrary root that will allow inspection of the Screen
-          list.push(suspense.id);
-        }
-
-        const stack = [suspense];
-        while (stack.length > 0) {
-          const current = stack.pop();
-          if (current === undefined) {
-            continue;
-          }
-          // Ignore any suspense boundaries that has no visual representation as this is not
-          // part of the visible loading sequence.
-          // TODO: Consider making visible meta data and other side-effects get virtual rects.
-          const hasRects =
-            current.rects !== null &&
-            current.rects.length > 0 &&
-            current.rects.some(isNonZeroRect);
-          if (
-            hasRects &&
-            (!uniqueSuspendersOnly || current.hasUniqueSuspenders) &&
-            // Roots are already included as part of the Screen
-            current.id !== rootID
-          ) {
-            list.push(current.id);
-          }
-          // Add children in reverse order to maintain document order
-          for (let j = current.children.length - 1; j >= 0; j--) {
-            const childSuspense = this.getSuspenseByID(current.children[j]);
-            if (childSuspense !== null) {
-              stack.push(childSuspense);
-            }
-          }
+        const environments = suspense.environments;
+        const environmentName =
+          environments.length > 0
+            ? environments[environments.length - 1]
+            : null;
+        if (rootStep === null) {
+          // Arbitrarily use the first root as the root step id.
+          rootStep = {
+            id: suspense.id,
+            environment: environmentName,
+          };
+          target.push(rootStep);
+        } else if (rootStep.environment === null) {
+          // If any root has an environment name, then let's use it.
+          rootStep.environment = environmentName;
         }
+        this.pushTimelineStepsInDocumentOrder(
+          suspense.children,
+          target,
+          uniqueSuspendersOnly,
+          environments,
+        );
       }
     }
 
-    return list;
+    return target;
+  }
+
+  pushTimelineStepsInDocumentOrder(
+    children: Array<SuspenseNode['id']>,
+    target: Array<SuspenseTimelineStep>,
+    uniqueSuspendersOnly: boolean,
+    parentEnvironments: Array<string>,
+  ): void {
+    for (let i = 0; i < children.length; i++) {
+      const child = this.getSuspenseByID(children[i]);
+      if (child === null) {
+        continue;
+      }
+      // Ignore any suspense boundaries that has no visual representation as this is not
+      // part of the visible loading sequence.
+      // TODO: Consider making visible meta data and other side-effects get virtual rects.
+      const hasRects =
+        child.rects !== null &&
+        child.rects.length > 0 &&
+        child.rects.some(isNonZeroRect);
+      const childEnvironments = child.environments;
+      // Since children are blocked on the parent, they're also blocked by the parent environments.
+      // Only if we discover a novel environment do we add that and it becomes the name we use.
+      const unionEnvironments = unionOfTwoArrays(
+        parentEnvironments,
+        childEnvironments,
+      );
+      const environmentName =
+        unionEnvironments.length > 0
+          ? unionEnvironments[unionEnvironments.length - 1]
+          : null;
+      if (hasRects && (!uniqueSuspendersOnly || child.hasUniqueSuspenders)) {
+        target.push({
+          id: child.id,
+          environment: environmentName,
+        });
+      }
+      this.pushTimelineStepsInDocumentOrder(
+        child.children,
+        target,
+        uniqueSuspendersOnly,
+        unionEnvironments,
+      );
+    }
   }
 
   getRendererIDForElement(id: number): number | null {
@@ -1627,6 +1658,7 @@ export default class Store extends EventEmitter<{
             rects,
             hasUniqueSuspenders: false,
             isSuspended: isSuspended,
+            environments: [],
           });
 
           hasSuspenseTreeChanged = true;
@@ -1812,7 +1844,10 @@ export default class Store extends EventEmitter<{
               envIndex++
             ) {
               const environmentNameStringID = operations[i++];
-              environmentNames.push(stringTable[environmentNameStringID]);
+              const environmentName = stringTable[environmentNameStringID];
+              if (environmentName != null) {
+                environmentNames.push(environmentName);
+              }
             }
             const suspense = this._idToSuspense.get(id);
 
@@ -1836,7 +1871,7 @@ export default class Store extends EventEmitter<{
 
             suspense.hasUniqueSuspenders = hasUniqueSuspenders;
             suspense.isSuspended = isSuspended;
-            // TODO: Recompute the environment names.
+            suspense.environments = environmentNames;
           }
 
           hasSuspenseTreeChanged = true;

packages/react-devtools-shared/src/devtools/views/SuspenseTab/SuspenseRects.js

@@ -154,7 +154,8 @@ function SuspenseRects({
   const selected = inspectedElementID === suspenseID;
 
   const hovered =
-    hoveredTimelineIndex > -1 && timeline[hoveredTimelineIndex] === suspenseID;
+    hoveredTimelineIndex > -1 &&
+    timeline[hoveredTimelineIndex].id === suspenseID;
 
   const boundingBox = getBoundingBox(suspense.rects);
 

packages/react-devtools-shared/src/devtools/views/SuspenseTab/SuspenseTimeline.js

@@ -34,7 +34,7 @@ function SuspenseTimelineInput() {
   const max = timeline.length > 0 ? timeline.length - 1 : 0;
 
   function switchSuspenseNode(nextTimelineIndex: number) {
-    const nextSelectedSuspenseID = timeline[nextTimelineIndex];
+    const nextSelectedSuspenseID = timeline[nextTimelineIndex].id;
     treeDispatch({
       type: 'SELECT_ELEMENT_BY_ID',
       payload: nextSelectedSuspenseID,
@@ -54,7 +54,7 @@ function SuspenseTimelineInput() {
   }
 
   function handleHoverSegment(hoveredIndex: number) {
-    const nextSelectedSuspenseID = timeline[hoveredIndex];
+    const nextSelectedSuspenseID = timeline[hoveredIndex].id;
     suspenseTreeDispatch({
       type: 'HOVER_TIMELINE_FOR_ID',
       payload: nextSelectedSuspenseID,
@@ -68,7 +68,7 @@ function SuspenseTimelineInput() {
   }
 
   function skipPrevious() {
-    const nextSelectedSuspenseID = timeline[timelineIndex - 1];
+    const nextSelectedSuspenseID = timeline[timelineIndex - 1].id;
     treeDispatch({
       type: 'SELECT_ELEMENT_BY_ID',
       payload: nextSelectedSuspenseID,
@@ -80,7 +80,7 @@ function SuspenseTimelineInput() {
   }
 
   function skipForward() {
-    const nextSelectedSuspenseID = timeline[timelineIndex + 1];
+    const nextSelectedSuspenseID = timeline[timelineIndex + 1].id;
     treeDispatch({
       type: 'SELECT_ELEMENT_BY_ID',
       payload: nextSelectedSuspenseID,
@@ -106,7 +106,7 @@ function SuspenseTimelineInput() {
     // anything suspended in the root. The step after that should have one less
     // thing suspended. I.e. the first suspense boundary should be unsuspended
     // when it's selected. This also lets you show everything in the last step.
-    const suspendedSet = timeline.slice(timelineIndex + 1);
+    const suspendedSet = timeline.slice(timelineIndex + 1).map(step => step.id);
     bridge.send('overrideSuspenseMilestone', {
       suspendedSet,
     });