Store tags rather than IDs for pending scroll/hover

Following https://github.com/hypothesis/client/pull/4962, we can now identify
annotations that should be scrolled to/focused after they anchor by their tag
rather than ID, since the annotation in the sidebar's store persists across the
chapter navigation.

src/sidebar/services/frame-sync.ts

@@ -127,22 +127,19 @@ export class FrameSyncService {
   private _store: SidebarStore;
 
   /**
-   * ID of an annotation that should be scrolled to after anchoring completes.
+   * Tag of an annotation that should be scrolled to after anchoring completes.
    *
    * This is set when {@link scrollToAnnotation} is called and the document
    * needs to be navigated to a different URL. This can happen in EPUBs.
-   *
-   * We store an ID rather than a tag because the navigation currently triggers
-   * a reload of annotations, which will change their tags but not their IDs.
    */
-  private _pendingScrollToId: string | null;
+  private _pendingScrollToTag: string | null;
 
   /**
-   * ID of an annotation that should be hovered after anchoring completes.
+   * Tag of an annotation that should be hovered after anchoring completes.
    *
-   * See notes for {@link _pendingScrollToId}.
+   * See notes for {@link _pendingScrollToTag}.
    */
-  private _pendingHoverId: string | null;
+  private _pendingHoverTag: string | null;
 
   // Test seam
   private _window: Window;
@@ -166,8 +163,8 @@ export class FrameSyncService {
     this._inFrame = new Set<string>();
     this._highlightsVisible = false;
 
-    this._pendingScrollToId = null;
-    this._pendingHoverId = null;
+    this._pendingScrollToTag = null;
+    this._pendingHoverTag = null;
 
     this._setupSyncToGuests();
     this._setupHostEvents();
@@ -376,14 +373,13 @@ export class FrameSyncService {
       anchoringStatusUpdates[$tag] = $orphan ? 'orphan' : 'anchored';
       scheduleAnchoringStatusUpdate();
 
-      const [id] = this._store.findIDsForTags([$tag]);
-      if (id === this._pendingHoverId) {
-        this._pendingHoverId = null;
+      if ($tag === this._pendingHoverTag) {
+        this._pendingHoverTag = null;
         guestRPC.call('hoverAnnotations', [$tag]);
       }
-      if (this._pendingScrollToId) {
-        if (id === this._pendingScrollToId) {
-          this._pendingScrollToId = null;
+      if (this._pendingScrollToTag) {
+        if ($tag === this._pendingScrollToTag) {
+          this._pendingScrollToTag = null;
           guestRPC.call('scrollToAnnotation', $tag);
         }
       }
@@ -532,7 +528,7 @@ export class FrameSyncService {
    * user can hover multiple highlights in the document at once.
    */
   hoverAnnotation(ann: Annotation | null) {
-    this._pendingHoverId = null;
+    this._pendingHoverTag = null;
 
     if (!ann) {
       this._guestRPC.forEach(rpc => rpc.call('hoverAnnotations', []));
@@ -551,9 +547,7 @@ export class FrameSyncService {
       !frame ||
       (frame.segment && !annotationMatchesSegment(ann, frame.segment))
     ) {
-      if (ann.id) {
-        this._pendingHoverId = ann.id;
-      }
+      this._pendingHoverTag = ann.$tag;
       return;
     }
     this._guestRPC.forEach(rpc => rpc.call('hoverAnnotations', tags));
@@ -580,10 +574,8 @@ export class FrameSyncService {
     // the annotation to anchor in the new guest frame before we can actually
     // scroll to it.
     if (frame.segment && !annotationMatchesSegment(ann, frame.segment)) {
-      if (ann.id) {
       // Schedule scroll once anchoring completes.
-        this._pendingScrollToId = ann.id;
-      }
+      this._pendingScrollToTag = ann.$tag;
       guest.call('navigateToSegment', formatAnnot(ann));
       return;
     }

src/sidebar/services/test/frame-sync-test.js

@@ -947,7 +947,6 @@ describe('FrameSyncService', () => {
 
       // Create an annotation with a CFI that doesn't match `fixtures.epubDocumentInfo`.
       const ann = createEPUBAnnotation('/4/8');
-      fakeStore.findIDsForTags.withArgs([ann.$tag]).returns([ann.id]);
 
       // Request hover of annotation. The annotation is marked as hovered in
       // the sidebar, but nothing is sent to the guest since the annotation's
@@ -1001,7 +1000,6 @@ describe('FrameSyncService', () => {
 
       // Create an annotation with a CFI that doesn't match `fixtures.epubDocumentInfo`.
       const ann = createEPUBAnnotation('/4/8');
-      fakeStore.findIDsForTags.withArgs([ann.$tag]).returns([ann.id]);
 
       // Request a scroll to this annotation, this will require a navigation of
       // the guest frame.