Make FlatList permissive of ArrayLike data (#36236)

Summary:
Pull Request resolved: #36236

D38198351 (d574ea3) addedd a guard to FlatList, to no-op if passed `data` that was not an array. This broke functionality where Realm had documented using `Realm.Results` with FlatList. `Real.Results` is an array-like JSI object, but not actually an array, and fails any `Array.isArray()` checks.

This change loosens the FlatList contract, to explicitly allow array-like non-array entities. The requirement align to Flow `ArrayLike`, which allows both arrays, and objects which provide a length and indexer. Flow `$ArrayLike` currently also requires an iterator, but this is seemingly a mistake in the type definition, and not enforced.

Though `Realm.Results` has all the methods of TS `ReadonlyArray`, RN has generally assumes its array inputs will pass `Array.isArray()`. This includes any array props still being checked [via prop-types](https://github.com/facebook/prop-types/blob/044efd7a108556c7660f6b62092756666e39d74b/factoryWithTypeCheckers.js#L548).

This change intentionally does not yet change the parameter type of `getItemLayout()`, which is already too loose (allowing mutable arrays). Changing this is a breaking change, that would be disruptive to backport, so we separate it into a different commit that will be landed as part of 0.72 (see next diff in the stack).

Changelog:
[General][Changed] - Make FlatList permissive of ArrayLike data

Reviewed By: yungsters

Differential Revision: D43465654

fbshipit-source-id: 3ed8c76c15da680560d7639b7cc43272f3e46ac3

Author: NickGerleman

Libraries/Lists/FlatList.d.ts

@@ -14,9 +14,9 @@ import type {
   VirtualizedListProps,
 } from '@react-native/virtualized-lists';
 import type {ScrollViewComponent} from '../Components/ScrollView/ScrollView';
-import {StyleProp} from '../StyleSheet/StyleSheet';
-import {ViewStyle} from '../StyleSheet/StyleSheetTypes';
-import {View} from '../Components/View/View';
+import type {StyleProp} from '../StyleSheet/StyleSheet';
+import type {ViewStyle} from '../StyleSheet/StyleSheetTypes';
+import type {View} from '../Components/View/View';
 
 export interface FlatListProps<ItemT> extends VirtualizedListProps<ItemT> {
   /**
@@ -40,10 +40,10 @@ export interface FlatListProps<ItemT> extends VirtualizedListProps<ItemT> {
     | undefined;
 
   /**
-   * For simplicity, data is just a plain array. If you want to use something else,
-   * like an immutable list, use the underlying VirtualizedList directly.
+   * An array (or array-like list) of items to render. Other data types can be
+   * used by targetting VirtualizedList directly.
    */
-  data: ReadonlyArray<ItemT> | null | undefined;
+  data: ArrayLike<ItemT> | null | undefined;
 
   /**
    * A marker property for telling the list to re-render (since it implements PureComponent).

Libraries/Lists/FlatList.js

@@ -33,10 +33,10 @@ const React = require('react');
 
 type RequiredProps<ItemT> = {|
   /**
-   * For simplicity, data is just a plain array. If you want to use something else, like an
-   * immutable list, use the underlying `VirtualizedList` directly.
+   * An array (or array-like list) of items to render. Other data types can be
+   * used by targetting VirtualizedList directly.
    */
-  data: ?$ReadOnlyArray<ItemT>,
+  data: ?$ArrayLike<ItemT>,
 |};
 type OptionalProps<ItemT> = {|
   /**
@@ -166,6 +166,11 @@ function numColumnsOrDefault(numColumns: ?number) {
   return numColumns ?? 1;
 }
 
+function isArrayLike(data: mixed): boolean {
+  // $FlowExpectedError[incompatible-use]
+  return typeof Object(data).length === 'number';
+}
+
 type FlatListProps<ItemT> = {|
   ...RequiredProps<ItemT>,
   ...OptionalProps<ItemT>,
@@ -500,8 +505,10 @@ class FlatList<ItemT> extends React.PureComponent<Props<ItemT>, void> {
     );
   }
 
-  // $FlowFixMe[missing-local-annot]
-  _getItem = (data: Array<ItemT>, index: number) => {
+  _getItem = (
+    data: $ArrayLike<ItemT>,
+    index: number,
+  ): ?(ItemT | $ReadOnlyArray<ItemT>) => {
     const numColumns = numColumnsOrDefault(this.props.numColumns);
     if (numColumns > 1) {
       const ret = [];
@@ -518,8 +525,14 @@ class FlatList<ItemT> extends React.PureComponent<Props<ItemT>, void> {
     }
   };
 
-  _getItemCount = (data: ?Array<ItemT>): number => {
-    if (Array.isArray(data)) {
+  _getItemCount = (data: ?$ArrayLike<ItemT>): number => {
+    // Legacy behavior of FlatList was to forward "undefined" length if invalid
+    // data like a non-arraylike object is passed. VirtualizedList would then
+    // coerce this, and the math would work out to no-op. For compatibility, if
+    // invalid data is passed, we tell VirtualizedList there are zero items
+    // available to prevent it from trying to read from the invalid data
+    // (without propagating invalidly typed data).
+    if (data != null && isArrayLike(data)) {
       const numColumns = numColumnsOrDefault(this.props.numColumns);
       return numColumns > 1 ? Math.ceil(data.length / numColumns) : data.length;
     } else {

Libraries/Lists/__tests__/FlatList-test.js

@@ -182,4 +182,29 @@ describe('FlatList', () => {
 
     expect(renderItemInThreeColumns).toHaveBeenCalledTimes(7);
   });
+  it('renders array-like data', () => {
+    const arrayLike = {
+      length: 3,
+      0: {key: 'i1'},
+      1: {key: 'i2'},
+      2: {key: 'i3'},
+    };
+
+    const component = ReactTestRenderer.create(
+      <FlatList
+        data={arrayLike}
+        renderItem={({item}) => <item value={item.key} />}
+      />,
+    );
+    expect(component).toMatchSnapshot();
+  });
+  it('ignores invalid data', () => {
+    const component = ReactTestRenderer.create(
+      <FlatList
+        data={123456}
+        renderItem={({item}) => <item value={item.key} />}
+      />,
+    );
+    expect(component).toMatchSnapshot();
+  });
 });

Libraries/Lists/__tests__/__snapshots__/FlatList-test.js.snap

@@ -1,5 +1,63 @@
 // Jest Snapshot v1, https://goo.gl/fbAQLP
 
+exports[`FlatList ignores invalid data 1`] = `
+<RCTScrollView
+  alwaysBounceVertical={true}
+  data={123456}
+  getItem={[Function]}
+  getItemCount={[Function]}
+  keyExtractor={[Function]}
+  onContentSizeChange={null}
+  onLayout={[Function]}
+  onMomentumScrollBegin={[Function]}
+  onMomentumScrollEnd={[Function]}
+  onResponderGrant={[Function]}
+  onResponderReject={[Function]}
+  onResponderRelease={[Function]}
+  onResponderTerminationRequest={[Function]}
+  onScroll={[Function]}
+  onScrollBeginDrag={[Function]}
+  onScrollEndDrag={[Function]}
+  onScrollShouldSetResponder={[Function]}
+  onStartShouldSetResponder={[Function]}
+  onStartShouldSetResponderCapture={[Function]}
+  onTouchCancel={[Function]}
+  onTouchEnd={[Function]}
+  onTouchMove={[Function]}
+  onTouchStart={[Function]}
+  pagingEnabled={false}
+  removeClippedSubviews={false}
+  renderItem={[Function]}
+  scrollEventThrottle={50}
+  scrollViewRef={[Function]}
+  sendMomentumEvents={true}
+  snapToEnd={true}
+  snapToStart={true}
+  stickyHeaderIndices={Array []}
+  style={
+    Object {
+      "flexDirection": "column",
+      "flexGrow": 1,
+      "flexShrink": 1,
+      "overflow": "scroll",
+    }
+  }
+  viewabilityConfigCallbackPairs={Array []}
+>
+  <RCTScrollContentView
+    collapsable={false}
+    onLayout={[Function]}
+    removeClippedSubviews={false}
+    style={
+      Array [
+        false,
+        undefined,
+      ]
+    }
+  />
+</RCTScrollView>
+`;
+
 exports[`FlatList renders all the bells and whistles 1`] = `
 <RCTScrollView
   ItemSeparatorComponent={[Function]}
@@ -122,6 +180,105 @@ exports[`FlatList renders all the bells and whistles 1`] = `
 </RCTScrollView>
 `;
 
+exports[`FlatList renders array-like data 1`] = `
+<RCTScrollView
+  alwaysBounceVertical={true}
+  data={
+    Object {
+      "0": Object {
+        "key": "i1",
+      },
+      "1": Object {
+        "key": "i2",
+      },
+      "2": Object {
+        "key": "i3",
+      },
+      "length": 3,
+    }
+  }
+  getItem={[Function]}
+  getItemCount={[Function]}
+  keyExtractor={[Function]}
+  onContentSizeChange={null}
+  onLayout={[Function]}
+  onMomentumScrollBegin={[Function]}
+  onMomentumScrollEnd={[Function]}
+  onResponderGrant={[Function]}
+  onResponderReject={[Function]}
+  onResponderRelease={[Function]}
+  onResponderTerminationRequest={[Function]}
+  onScroll={[Function]}
+  onScrollBeginDrag={[Function]}
+  onScrollEndDrag={[Function]}
+  onScrollShouldSetResponder={[Function]}
+  onStartShouldSetResponder={[Function]}
+  onStartShouldSetResponderCapture={[Function]}
+  onTouchCancel={[Function]}
+  onTouchEnd={[Function]}
+  onTouchMove={[Function]}
+  onTouchStart={[Function]}
+  pagingEnabled={false}
+  removeClippedSubviews={false}
+  renderItem={[Function]}
+  scrollEventThrottle={50}
+  scrollViewRef={[Function]}
+  sendMomentumEvents={true}
+  snapToEnd={true}
+  snapToStart={true}
+  stickyHeaderIndices={Array []}
+  style={
+    Object {
+      "flexDirection": "column",
+      "flexGrow": 1,
+      "flexShrink": 1,
+      "overflow": "scroll",
+    }
+  }
+  viewabilityConfigCallbackPairs={Array []}
+>
+  <RCTScrollContentView
+    collapsable={false}
+    onLayout={[Function]}
+    removeClippedSubviews={false}
+    style={
+      Array [
+        false,
+        undefined,
+      ]
+    }
+  >
+    <View
+      onFocusCapture={[Function]}
+      onLayout={[Function]}
+      style={null}
+    >
+      <item
+        value="i1"
+      />
+    </View>
+    <View
+      onFocusCapture={[Function]}
+      onLayout={[Function]}
+      style={null}
+    >
+      <item
+        value="i2"
+      />
+    </View>
+    <View
+      onFocusCapture={[Function]}
+      onLayout={[Function]}
+      style={null}
+    >
+      <item
+        value="i3"
+      />
+    </View>
+  </RCTScrollContentView>
+</RCTScrollView>
+`;
+
 exports[`FlatList renders empty list 1`] = `
 <RCTScrollView
   data={Array []}