From a150669a66811c6bff3e15f8442ac80dc969d657 Mon Sep 17 00:00:00 2001
From: brysonbw <brysonward77@gmail.com>
Date: Tue, 11 Aug 2026 04:50:28 -0500
Subject: [PATCH] feat(router): add containsTree as public API

Export containsTree from @angular/router to enable direct UrlTree subset matching.
---
 goldens/public-api/router/index.api.md | 3 +++
 packages/router/src/index.ts           | 1 +
 packages/router/src/url_tree.ts        | 9 +++++++++
 3 files changed, 13 insertions(+)

diff --git a/goldens/public-api/router/index.api.md b/goldens/public-api/router/index.api.md
index 765ae315633..6d5b76838dd 100644
--- a/goldens/public-api/router/index.api.md
+++ b/goldens/public-api/router/index.api.md
@@ -205,6 +205,9 @@ export interface ComponentInputBindingOptions {
     unmatchedInputBehavior?: 'alwaysUndefined' | 'undefinedIfStale';
 }
 
+// @public
+export function containsTree(container: UrlTree, containee: UrlTree, options: IsActiveMatchOptions): boolean;
+
 // @public
 export function convertToParamMap(params: Params): ParamMap;
 
diff --git a/packages/router/src/index.ts b/packages/router/src/index.ts
index 6513a0d7044..abfa4b04e49 100644
--- a/packages/router/src/index.ts
+++ b/packages/router/src/index.ts
@@ -140,6 +140,7 @@ export {
   UrlSegmentGroup,
   UrlSerializer,
   UrlTree,
+  containsTree,
 } from './url_tree';
 export {
   mapToCanActivate,
diff --git a/packages/router/src/url_tree.ts b/packages/router/src/url_tree.ts
index ee6853cc087..38a9fc31e7c 100644
--- a/packages/router/src/url_tree.ts
+++ b/packages/router/src/url_tree.ts
@@ -130,6 +130,15 @@ export function isActive(
   );
 }
 
+/**
+ * Determines if a `UrlTree` is contained within another `UrlTree` based on the provided matching options.
+ *
+ * @param container The outer or reference `UrlTree`.
+ * @param containee The target `UrlTree` to test against the container.
+ * @param options Matching rules for paths, matrix parameters, query parameters, and fragments.
+ *
+ * @publicApi
+ */
 export function containsTree(
   container: UrlTree,
   containee: UrlTree,