Fix back swipe opening the drawer after a cold-start deep link (#11065)

Co-authored-by: Claude <noreply@anthropic.com>

__tests__/lib/routes-helpers.test.ts

@@ -0,0 +1,107 @@
+import {
+  buildStateObject,
+  getCurrentRoute,
+  isStateAtTabRoot,
+} from '#/lib/routes/helpers'
+import {type State} from '#/lib/routes/types'
+
+describe('getCurrentRoute', () => {
+  it('returns Home when there is no state', () => {
+    expect(getCurrentRoute(undefined).name).toBe('Home')
+  })
+
+  it('descends into nested state using the index', () => {
+    const state = {
+      index: 0,
+      routes: [
+        {
+          name: 'HomeTab',
+          state: {
+            index: 1,
+            routes: [{name: 'Home'}, {name: 'PostThread'}],
+          },
+        },
+      ],
+    } as unknown as State
+
+    expect(getCurrentRoute(state).name).toBe('PostThread')
+  })
+
+  /*
+   * Right after a cold start from a deep link, nested navigator states are
+   * still partial and have no `index`. React Navigation focuses the last
+   * route when rehydrating such a state, so getCurrentRoute must do the
+   * same (previously it stopped at the tab route, which re-enabled the
+   * drawer swipe gesture on top of the deep-linked screen).
+   */
+  it('descends into partial nested state without an index', () => {
+    const state = {
+      routes: [
+        {
+          name: 'HomeTab',
+          state: {
+            routes: [{name: 'Home'}, {name: 'PostThread'}],
+          },
+        },
+      ],
+    } as unknown as State
+
+    expect(getCurrentRoute(state).name).toBe('PostThread')
+  })
+})
+
+describe('isStateAtTabRoot', () => {
+  it('returns true for the initial deep link state of a tab root', () => {
+    const state = buildStateObject('HomeTab', 'Home', {}) as unknown as State
+    expect(isStateAtTabRoot(state)).toBe(true)
+  })
+
+  it('returns false for the initial deep link state of a nested screen', () => {
+    const state = buildStateObject(
+      'HomeTab',
+      'PostThread',
+      {name: 'alice.test', rkey: '123'},
+      [{name: 'Home', params: {}}],
+    ) as unknown as State
+    expect(isStateAtTabRoot(state)).toBe(false)
+  })
+})
+
+describe('buildStateObject', () => {
+  it('focuses the deep-linked route in the nested state', () => {
+    const state = buildStateObject(
+      'HomeTab',
+      'PostThread',
+      {name: 'alice.test', rkey: '123'},
+      [{name: 'Home', params: {}}],
+    )
+
+    expect(state).toEqual({
+      index: 0,
+      routes: [
+        {
+          name: 'HomeTab',
+          state: {
+            index: 1,
+            routes: [
+              {name: 'Home', params: {}},
+              {name: 'PostThread', params: {name: 'alice.test', rkey: '123'}},
+            ],
+          },
+        },
+      ],
+    })
+  })
+
+  it('builds a single-route state for the Flat navigator', () => {
+    const state = buildStateObject('Flat', 'PostThread', {
+      name: 'alice.test',
+      rkey: '123',
+    })
+
+    expect(state).toEqual({
+      index: 0,
+      routes: [{name: 'PostThread', params: {name: 'alice.test', rkey: '123'}}],
+    })
+  })
+})

src/Navigation.tsx

@@ -30,7 +30,7 @@ import {
 } from '#/lib/hooks/useNotificationHandler'
 import {useWebScrollRestoration} from '#/lib/hooks/useWebScrollRestoration'
 import {useCallOnce} from '#/lib/once'
-import {buildStateObject} from '#/lib/routes/helpers'
+import {buildStateObject, getCurrentRoute} from '#/lib/routes/helpers'
 import {
   type AllNavigatorParams,
   type BottomTabNavigatorParams,
@@ -783,10 +783,7 @@ const LINKING = {
 
   getPathFromState(state: State) {
     // find the current node in the navigation tree
-    let node = state.routes[state.index || 0]
-    while (node.state?.routes && typeof node.state?.index === 'number') {
-      node = node.state?.routes[node.state?.index]
-    }
+    const node = getCurrentRoute(state)
 
     // build the path
     const route = router.matchName(node.name)

src/lib/routes/helpers.ts

@@ -13,12 +13,20 @@ export function getRootNavigation<T extends {}>(
 
 export function getCurrentRoute(state?: State) {
   if (!state) {
-    return {name: 'Home'}
+    return {name: 'Home', params: undefined}
   }
 
+  /*
+   * Nested navigator states may still be partial ("stale") right after a cold
+   * start from a deep link, in which case `index` is not set yet. React
+   * Navigation focuses the last route when it rehydrates such a state, so
+   * mirror that here instead of stopping the descent early and misreporting
+   * the tab root as the current route (which e.g. re-enabled the drawer
+   * swipe gesture on top of a deep-linked screen).
+   */
   let node = state.routes[state.index || 0]
-  while (node.state?.routes && typeof node.state?.index === 'number') {
-    node = node.state?.routes[node.state?.index]
+  while (node.state?.routes) {
+    node = node.state.routes[node.state.index ?? node.state.routes.length - 1]
   }
   return node
 }
@@ -83,15 +91,24 @@ export function buildStateObject(
 ) {
   if (stack === 'Flat') {
     return {
+      index: 0,
       routes: [{name: route, params}],
     }
   }
+  /*
+   * Set `index` explicitly so consumers of this state (e.g. getCurrentRoute)
+   * can tell which route is focused before React Navigation has rehydrated
+   * the nested navigator state.
+   */
+  const routes = [...state, {name: route, params}]
   return {
+    index: 0,
     routes: [
       {
         name: stack,
         state: {
-          routes: [...state, {name: route, params}],
+          index: routes.length - 1,
+          routes,
         },
       },
     ],