introduce Fantom.scrollTo (#48907)

Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/48907

changelog: [internal]

Introduce new function `Fantom.scrollTo`, which will fake a scroll to particular position.
Calling the method will call onScroll event using codepath that iOS uses. It will also set C++ state so the new scroll position is observable from JavaScript.

Reviewed By: javache

Differential Revision: D68554703

fbshipit-source-id: 2fc71e96836a03ec343053ceed85764c4bc2f5c7

packages/react-native-fantom/src/__tests__/Fantom-itest.js

@@ -473,4 +473,108 @@ describe('Fantom', () => {
       y: 2,
     });
   });
+
+  describe('scrollTo', () => {
+    it('throws error if called on node that is not scroll view', () => {
+      const root = Fantom.createRoot();
+      let maybeNode;
+
+      Fantom.runTask(() => {
+        root.render(
+          <View
+            ref={node => {
+              maybeNode = node;
+            }}
+          />,
+        );
+      });
+
+      const element = ensureInstance(maybeNode, ReactNativeElement);
+
+      expect(() => {
+        Fantom.runOnUIThread(() => {
+          Fantom.scrollTo(element, {
+            x: 0,
+            y: 1,
+          });
+        });
+      }).toThrow(
+        'Exception in HostFunction: scrollTo() can only be called on <ScrollView />',
+      );
+    });
+
+    it('delivers onScroll event and affects position of elements on screen', () => {
+      const root = Fantom.createRoot();
+      let maybeScrollViewNode;
+      let maybeNode;
+      const onScroll = jest.fn();
+
+      Fantom.runTask(() => {
+        root.render(
+          <ScrollView
+            onScroll={event => {
+              onScroll(event.nativeEvent);
+            }}
+            ref={node => {
+              maybeScrollViewNode = node;
+            }}>
+            <View
+              style={{width: 1, height: 2, top: 3}}
+              ref={node => {
+                maybeNode = node;
+              }}
+            />
+          </ScrollView>,
+        );
+      });
+
+      const scrollViewElement = ensureInstance(
+        maybeScrollViewNode,
+        ReactNativeElement,
+      );
+
+      Fantom.runOnUIThread(() => {
+        Fantom.scrollTo(scrollViewElement, {
+          x: 0,
+          y: 1,
+        });
+      });
+
+      Fantom.runWorkLoop();
+
+      expect(onScroll).toHaveBeenCalledTimes(1);
+
+      const viewElement = ensureInstance(maybeNode, ReactNativeElement);
+
+      let rect;
+
+      viewElement.measure((x, y, width, height, pageX, pageY) => {
+        rect = {
+          x,
+          y,
+          width,
+          height,
+          pageX,
+          pageY,
+        };
+      });
+
+      expect(rect).toEqual({
+        x: 0,
+        y: 3,
+        width: 1,
+        height: 2,
+        pageY: 2,
+        pageX: 0,
+      });
+
+      const boundingClientRect = viewElement.getBoundingClientRect();
+      expect(boundingClientRect.x).toBe(0);
+      expect(boundingClientRect.y).toBe(2);
+      expect(boundingClientRect.width).toBe(1);
+      expect(boundingClientRect.height).toBe(2);
+
+      root.destroy();
+    });
+  });
 });

packages/react-native-fantom/src/index.js

@@ -167,6 +167,16 @@ function dispatchNativeEvent(
   );
 }
 
+function scrollTo(
+  node: ReactNativeElement,
+  options: {x: number, y: number, zoomScale?: number},
+) {
+  const shadowNode = getShadowNode(node);
+  NativeFantom.scrollTo(shadowNode, options);
+}
+
+export const unstable_benchmark = Benchmark;
+
 type FantomConstants = $ReadOnly<{
   isRunningFromCI: boolean,
 }>;
@@ -255,4 +265,5 @@ export default {
   createRoot,
   dispatchNativeEvent,
   unstable_benchmark: Benchmark,
+  scrollTo,
 };

packages/react-native/Libraries/__tests__/__snapshots__/public-api-test.js.snap

@@ -10465,6 +10465,11 @@ export enum NativeEventCategory {
   Discrete = 3,
   Continuous = 4,
 }
+export type ScrollOptions = {
+  x: number,
+  y: number,
+  zoomScale?: number,
+};
 interface Spec extends TurboModule {
   startSurface: (
     surfaceId: number,
@@ -10480,6 +10485,7 @@ interface Spec extends TurboModule {
     category?: NativeEventCategory,
     isUnique?: boolean
   ) => void;
+  scrollTo: (shadowNode: mixed, options: ScrollOptions) => void;
   getMountingManagerLogs: (surfaceId: number) => Array<string>;
   flushMessageQueue: () => void;
   flushEventQueue: () => void;

packages/react-native/src/private/specs/modules/NativeFantom.js

@@ -51,6 +51,12 @@ export enum NativeEventCategory {
   Continuous = 4,
 }
 
+export type ScrollOptions = {
+  x: number,
+  y: number,
+  zoomScale?: number,
+};
+
 interface Spec extends TurboModule {
   startSurface: (
     surfaceId: number,
@@ -66,6 +72,10 @@ interface Spec extends TurboModule {
     category?: NativeEventCategory,
     isUnique?: boolean,
   ) => void;
+  scrollTo: (
+    shadowNode: mixed /* ShadowNode */,
+    options: ScrollOptions,
+  ) => void;
   getMountingManagerLogs: (surfaceId: number) => Array<string>;
   flushMessageQueue: () => void;
   flushEventQueue: () => void;