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'}}],
+    })
+  })
+})