The New <Text> on iOS

Summary:
This is a complete rewrite of RCTText, the part of React Native which manages Text and TextInput components.

Key points:

* It's understandable now. It follows a simple architectural pattern, and it's easy to debug and iterate. Text flow layout is a first-class citizen in React Native layout system now, not just a wired special case. It also brings entirely new possibilities such as nested interleaving <Text> and <View> components.
* All <Text>-specific APIs were removed from UIManager and co (it's about ~16 public methods which were used exclusively only by <Text>).
* It relies on new Yoga measurement/cloning API and on-dirty handler. So, it removes built-in dirty propagation subsystem from RN completely.
* It caches string fragments properly and granularly on a per-node basis which makes updating text-containing components more performant.
* It does not instantiate UIView for virtual components which reduces memory utilization.
* It drastically improves <TextInput> capabilities (e.g. rich text inside single line <TextInput> is now supported).

Screenshots:
https://cl.ly/2j3r1V0L0324
https://cl.ly/3N2V3C3d3q3R

Reviewed By: mmmulani

Differential Revision: D6617326

fbshipit-source-id: 35d4d81b35c9870e9557d0211c0e934e6072a41e

Author: shergin

js/TextExample.ios.js

@@ -233,20 +233,8 @@ exports.examples = [
     render: function() {
       return (
         <Text>
-          The text
-          <View style={{borderColor: 'red', borderWidth: 1}}>
-            <Text style={{borderColor: 'blue', borderWidth: 1}}>Text Inside</Text>
-            <Text style={{borderColor: 'green', borderWidth: 1}}>Another text Inside</Text>
-            <Text style={{borderColor: 'yellow', borderWidth: 1}}>
-              Total inseption
-              <View style={{borderColor: 'red', borderWidth: 1}}>
-                <Text style={{borderColor: 'blue', borderWidth: 1}}>Insepted Text Inside</Text>
-              </View>
-            </Text>
-          </View>
           The text should wrap if it goes on multiple lines. See, this is going
           to the next line.
-          The text after.
         </Text>
       );
     },
@@ -759,6 +747,27 @@ exports.examples = [
       );
     },
   },
+  {
+    title: 'Nested content',
+    render: function() {
+      return (
+        <Text>
+          This text has a view
+          <View style={{borderColor: 'red', borderWidth: 1}}>
+            <Text style={{borderColor: 'blue', borderWidth: 1}}>which has</Text>
+            <Text style={{borderColor: 'green', borderWidth: 1}}>another text inside.</Text>
+            <Text style={{borderColor: 'yellow', borderWidth: 1}}>
+              And moreover, it has another view
+              <View style={{borderColor: 'red', borderWidth: 1}}>
+                <Text style={{borderColor: 'blue', borderWidth: 1}}>with another text inside!</Text>
+              </View>
+            </Text>
+          </View>
+          Because we need to go deeper.
+        </Text>
+      );
+    },
+  },
   {
     title: 'Dynamic Font Size Adjustment',
     render: function(): React.Element<any> {

js/TextInputExample.ios.js

@@ -18,6 +18,8 @@ var {
   TextInput,
   View,
   StyleSheet,
+  Slider,
+  Switch,
 } = ReactNative;
 
 class WithLabel extends React.Component<$FlowFixMeProps> {
@@ -335,6 +337,61 @@ class SelectionExample extends React.Component<$FlowFixMeProps, SelectionExample
   }
 }
 
+class AutogrowingTextInputExample extends React.Component<$FlowFixMeProps, $FlowFixMeState> {
+  constructor(props) {
+    super(props);
+
+    this.state = {
+      width: 100,
+      multiline: true,
+      text: '',
+      contentSize: {
+        width: 0,
+        height: 0,
+      },
+    };
+  }
+
+  componentWillReceiveProps(props) {
+    this.setState({
+      multiline: props.multiline,
+    });
+  }
+
+  render() {
+    var {style, multiline, ...props} = this.props;
+    return (
+      <View>
+        <Text>Width:</Text>
+        <Slider
+          value={100}
+          minimumValue={0}
+          maximumValue={100}
+          step={10}
+          onValueChange={(value) => this.setState({width: value})}
+        />
+        <Text>Multiline:</Text>
+        <Switch
+          value={this.state.multiline}
+          onValueChange={(value) => this.setState({multiline: value})}
+        />
+        <Text>TextInput:</Text>
+        <TextInput
+          value="prop"
+          multiline={this.state.multiline}
+          style={[style, {width: this.state.width + '%'}]}
+          onChangeText={(value) => this.setState({text: value})}
+          onContentSizeChange={(event) => this.setState({contentSize: event.nativeEvent.contentSize})}
+          {...props}
+        />
+        <Text>Plain text value representation:</Text>
+        <Text>{this.state.text}</Text>
+        <Text>Content Size: {JSON.stringify(this.state.contentSize)}</Text>
+      </View>
+    );
+  }
+}
+
 var styles = StyleSheet.create({
   page: {
     paddingBottom: 300,
@@ -478,6 +535,29 @@ exports.examples = [
       );
     }
   },
+  {
+    title: 'Nested content and `value` property',
+    render: function() {
+      return (
+        <View>
+          <WithLabel label="singleline">
+            <TextInput style={styles.default} value="(value property)">
+              (first raw text node)
+              <Text color="red">(internal raw text node)</Text>
+              (last raw text node)
+            </TextInput>
+          </WithLabel>
+          <WithLabel label="multiline">
+            <TextInput style={styles.default} multiline={true} value="(value property)">
+              (first raw text node)
+              <Text color="red">(internal raw text node)</Text>
+              (last raw text node)
+            </TextInput>
+          </WithLabel>
+        </View>
+      );
+    }
+  },
   {
     title: 'Keyboard types',
     render: function() {
@@ -854,6 +934,34 @@ exports.examples = [
       );
     }
   },
+  {
+    title: 'Auto-expanding',
+    render: function() {
+      return (
+        <View>
+          <AutogrowingTextInputExample
+            enablesReturnKeyAutomatically={true}
+            returnKeyType="done"
+            multiline={true}
+            style={{maxHeight: 400, minHeight: 20, paddingTop: 0, backgroundColor: '#eeeeee', color: 'blue'}}
+          >
+            <Text style={{fontSize: 30, color: 'green'}}>
+              huge
+            </Text>
+            generic generic generic
+            <Text style={{fontSize: 6, color: 'red'}}>
+              small small small small small small
+            </Text>
+            <Text>regular regular</Text>
+            <Text style={{fontSize: 30, color: 'green'}}>
+              huge huge huge huge huge
+            </Text>
+            generic generic generic
+          </AutogrowingTextInputExample>
+        </View>
+      );
+    }
+  },
   {
     title: 'Attributed text',
     render: function() {