fix(portal): replay queued portal operations in order

src/components/Portal/PortalHost.tsx

@@ -50,7 +50,9 @@ export default class PortalHost extends React.Component<Props> {
     const queue = this.queue;
 
     while (queue.length && manager) {
-      const action = queue.pop();
+      // Replay in the order the operations were recorded, otherwise portals
+      // that mounted in the same commit end up stacked in reverse.
+      const action = queue.shift();
       if (action) {
         switch (action.type) {
           case 'mount':
@@ -89,7 +91,7 @@ export default class PortalHost extends React.Component<Props> {
     } else {
       const op: Operation = { type: 'mount', key, children };
       const index = this.queue.findIndex(
-        (o) => o.type === 'mount' || (o.type === 'update' && o.key === key)
+        (o) => (o.type === 'mount' || o.type === 'update') && o.key === key
       );
 
       if (index > -1) {

src/components/__tests__/Portal.test.tsx

@@ -1,9 +1,14 @@
+import * as React from 'react';
 import { Text } from 'react-native';
 
 import { expect, it, jest } from '@jest/globals';
 
 import { render, screen } from '../../test-utils';
+import Dialog from '../Dialog/Dialog';
+import Modal from '../Modal';
 import Portal from '../Portal/Portal';
+import PortalHost, { PortalContext } from '../Portal/PortalHost';
+import type { PortalMethods } from '../Portal/PortalHost';
 
 jest.useRealTimers();
 
@@ -21,3 +26,98 @@ it('renders portal with siblings', async () => {
 
   expect(toJSON()).toMatchSnapshot();
 });
+
+it('renders portals in source order when mounted in the same commit', async () => {
+  await render(
+    <Portal.Host>
+      <Portal>
+        <Text testID="portal-content">first</Text>
+      </Portal>
+      <Portal>
+        <Text testID="portal-content">second</Text>
+      </Portal>
+      <Portal>
+        <Text testID="portal-content">third</Text>
+      </Portal>
+    </Portal.Host>
+  );
+
+  const portals = screen.getAllByTestId('portal-content');
+
+  expect(portals).toHaveLength(3);
+  expect(portals[0]).toBe(screen.getByText('first'));
+  expect(portals[1]).toBe(screen.getByText('second'));
+  expect(portals[2]).toBe(screen.getByText('third'));
+});
+
+it('stacks components mounted in the same commit in source order', async () => {
+  await render(
+    <Portal.Host>
+      <Portal>
+        <Modal visible onDismiss={() => {}}>
+          <Text testID="layer">modal</Text>
+        </Modal>
+      </Portal>
+      <Portal>
+        <Dialog visible onDismiss={() => {}}>
+          <Text testID="layer">dialog</Text>
+        </Dialog>
+      </Portal>
+    </Portal.Host>
+  );
+
+  // The last portal in source order is painted on top, so `dialog` has to come
+  // after `modal` in the rendered tree.
+  const layers = await screen.findAllByTestId('layer');
+
+  expect(layers).toHaveLength(2);
+  expect(layers[0]).toBe(screen.getByText('modal'));
+  expect(layers[1]).toBe(screen.getByText('dialog'));
+});
+
+it('keeps queued mounts of other portals when one of them is updated', async () => {
+  // Mirrors `PortalConsumer`: mounts from `componentDidMount`, then updates its
+  // own key. Both calls land before `PortalHost` attaches its manager, so they
+  // go through the queue.
+  class QueuedConsumer extends React.Component<{
+    manager: PortalMethods;
+    label: string;
+    update?: boolean;
+  }> {
+    componentDidMount() {
+      const key = this.props.manager.mount(
+        <Text testID="queued">{this.props.label}</Text>
+      );
+
+      if (this.props.update) {
+        this.props.manager.update(
+          key,
+          <Text testID="queued">{`${this.props.label} (updated)`}</Text>
+        );
+      }
+    }
+
+    render() {
+      return null;
+    }
+  }
+
+  await render(
+    <PortalHost>
+      <PortalContext.Consumer>
+        {(manager) => (
+          <>
+            <QueuedConsumer manager={manager} label="first" />
+            <QueuedConsumer manager={manager} label="second" update />
+          </>
+        )}
+      </PortalContext.Consumer>
+    </PortalHost>
+  );
+
+  // Deliberately order-independent: this asserts that no portal is lost, which
+  // is a separate concern from the order the queue is replayed in.
+  expect(screen.getAllByTestId('queued')).toHaveLength(2);
+  expect(screen.getByText('first')).toBeTruthy();
+  expect(screen.getByText('second (updated)')).toBeTruthy();
+});