Prepare coalesced resolution replay

internal/engine/history.go

@@ -179,28 +179,50 @@ func mergeHistoryAtPath(root **document.Node, path Path, incoming *document.Node
 // intent into that event rather than replay a child assignment a second time.
 func coalescedResolutionSnapshots(snapshots []resolutionSnapshot) []resolutionSnapshot {
 	groups := make([]resolutionSnapshot, 0, len(snapshots))
+	reasons := make([]map[string]struct{}, 0, len(snapshots))
+	dependencies := make([]map[string]struct{}, 0, len(snapshots))
+	var coverage pathPrefixIndex
 	for _, snapshot := range snapshots {
-		merged := false
-		for i := range groups {
-			if !pathContains(groups[i].change.Path, snapshot.change.Path) {
-				continue
+		pointer := snapshot.change.Path.String()
+		groupIndex := -1
+		coverage.visitAncestors(pointer, func(id int) {
+			if groupIndex < 0 || id < groupIndex {
+				groupIndex = id
 			}
+		})
+		if groupIndex >= 0 {
+			group := &groups[groupIndex]
 			for _, reason := range snapshot.change.Reasons {
-				groups[i].change.Reasons = appendUniqueString(groups[i].change.Reasons, reason)
+				if _, found := reasons[groupIndex][reason]; !found {
+					reasons[groupIndex][reason] = struct{}{}
+					group.change.Reasons = append(group.change.Reasons, reason)
+				}
 			}
 			for _, dependency := range snapshot.change.Dependencies {
-				groups[i].change.Dependencies = appendUniquePath(groups[i].change.Dependencies, dependency)
+				dependencyPointer := dependency.String()
+				if _, found := dependencies[groupIndex][dependencyPointer]; !found {
+					dependencies[groupIndex][dependencyPointer] = struct{}{}
+					group.change.Dependencies = append(group.change.Dependencies, dependency.clone())
+				}
 			}
 			if snapshot.change.Origin.Operation == ChangeNormalization {
-				groups[i].change.Origin.Operation = ChangeNormalization
+				group.change.Origin.Operation = ChangeNormalization
 			}
-			merged = true
-			break
+			continue
 		}
-		if !merged {
-			snapshot.change = cloneChange(snapshot.change)
-			groups = append(groups, snapshot)
+		snapshot.change = cloneChange(snapshot.change)
+		groups = append(groups, snapshot)
+		reasonSet := make(map[string]struct{}, len(snapshot.change.Reasons))
+		for _, reason := range snapshot.change.Reasons {
+			reasonSet[reason] = struct{}{}
 		}
+		reasons = append(reasons, reasonSet)
+		dependencySet := make(map[string]struct{}, len(snapshot.change.Dependencies))
+		for _, dependency := range snapshot.change.Dependencies {
+			dependencySet[dependency.String()] = struct{}{}
+		}
+		dependencies = append(dependencies, dependencySet)
+		coverage.insert(pointer, len(groups)-1)
 	}
 	return groups
 }