core-api: fix accidental global singletons in collectors

Co-authored-by: blam <ben@blam.sh>

packages/core-api/src/extensions/traversal.test.tsx

@@ -41,11 +41,14 @@ describe('discovery', () => {
       root,
       discoverers: [childDiscoverer],
       collectors: {
-        names: createCollector(Array<string>(), (acc, el) => {
-          if (typeof el.type === 'string') {
-            acc.push(el.type);
-          }
-        }),
+        names: createCollector(
+          () => Array<string>(),
+          (acc, el) => {
+            if (typeof el.type === 'string') {
+              acc.push(el.type);
+            }
+          },
+        ),
       },
     });
 
@@ -85,11 +88,14 @@ describe('discovery', () => {
           ),
       ],
       collectors: {
-        names: createCollector(Array<string>(), (acc, el) => {
-          if (typeof el.type === 'string') {
-            acc.push(el.type);
-          }
-        }),
+        names: createCollector(
+          () => Array<string>(),
+          (acc, el) => {
+            if (typeof el.type === 'string') {
+              acc.push(el.type);
+            }
+          },
+        ),
       },
     });
 

packages/core-api/src/extensions/traversal.ts

@@ -120,10 +120,10 @@ export function traverseElementTree<Results>(options: {
 }
 
 export function createCollector<Result, Context>(
-  initialResult: Result,
+  accumulatorFactory: () => Result,
   visit: ReturnType<Collector<Result, Context>>['visit'],
 ): Collector<Result, Context> {
-  return () => ({ accumulator: initialResult, visit });
+  return () => ({ accumulator: accumulatorFactory(), visit });
 }
 
 export function childDiscoverer(element: ReactElement): ReactNode {

packages/core-api/src/plugin/collectors.ts

@@ -34,7 +34,7 @@ import { getComponentData } from '../extensions';
 import { createCollector } from '../extensions/traversal';
 
 export const pluginCollector = createCollector(
-  new Set<BackstagePlugin>(),
+  () => new Set<BackstagePlugin>(),
   (acc, node) => {
     const plugin = getComponentData<BackstagePlugin>(node, 'core.plugin');
     if (plugin) {

packages/core-api/src/routing/collectors.tsx

@@ -20,7 +20,7 @@ import { getComponentData } from '../extensions';
 import { createCollector } from '../extensions/traversal';
 
 export const routeCollector = createCollector(
-  new Map<RouteRef, string>(),
+  () => new Map<RouteRef, string>(),
   (acc, node, parent) => {
     if (parent.props.element === node) {
       return;
@@ -51,7 +51,7 @@ export const routeCollector = createCollector(
 );
 
 export const routeParentCollector = createCollector(
-  new Map<RouteRef, RouteRef | undefined>(),
+  () => new Map<RouteRef, RouteRef | undefined>(),
   (acc, node, parent, parentRouteRef?: RouteRef) => {
     if (parent.props.element === node) {
       return parentRouteRef;