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

Libraries/Text/BaseText/RCTBaseTextShadowView.h

@@ -0,0 +1,26 @@
+/**
+ * Copyright (c) 2015-present, Facebook, Inc.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree. An additional grant
+ * of patent rights can be found in the PATENTS file in the same directory.
+ */
+
+#import <React/RCTShadowView.h>
+
+#import "RCTTextAttributes.h"
+
+NS_ASSUME_NONNULL_BEGIN
+
+extern NSString *const RCTBaseTextShadowViewEmbeddedShadowViewAttributeName;
+
+@interface RCTBaseTextShadowView : RCTShadowView
+
+@property (nonatomic, strong) RCTTextAttributes *textAttributes;
+
+- (NSAttributedString *)attributedTextWithBaseTextAttributes:(nullable RCTTextAttributes *)baseTextAttributes;
+
+@end
+
+NS_ASSUME_NONNULL_END

Libraries/Text/BaseText/RCTBaseTextShadowView.m

@@ -0,0 +1,125 @@
+/**
+ * Copyright (c) 2015-present, Facebook, Inc.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree. An additional grant
+ * of patent rights can be found in the PATENTS file in the same directory.
+ */
+
+#import "RCTBaseTextShadowView.h"
+
+#import <React/RCTShadowView+Layout.h>
+
+#import "RCTRawTextShadowView.h"
+#import "RCTVirtualTextShadowView.h"
+
+NSString *const RCTBaseTextShadowViewEmbeddedShadowViewAttributeName = @"RCTBaseTextShadowViewEmbeddedShadowViewAttributeName";
+
+@implementation RCTBaseTextShadowView
+{
+  NSAttributedString *_Nullable _cachedAttributedText;
+  RCTTextAttributes *_Nullable _cachedTextAttributes;
+}
+
+- (instancetype)init
+{
+  if (self = [super init]) {
+    _textAttributes = [RCTTextAttributes new];
+  }
+
+  return self;
+}
+
+- (void)setReactTag:(NSNumber *)reactTag
+{
+  [super setReactTag:reactTag];
+  _textAttributes.tag = reactTag;
+}
+
+#pragma mark - attributedString
+
+- (NSAttributedString *)attributedTextWithBaseTextAttributes:(nullable RCTTextAttributes *)baseTextAttributes
+{
+  RCTTextAttributes *textAttributes;
+
+  if (baseTextAttributes) {
+    textAttributes = [baseTextAttributes copy];
+    [textAttributes applyTextAttributes:self.textAttributes];
+  } else {
+    textAttributes = [self.textAttributes copy];
+  }
+
+  if (_cachedAttributedText && [_cachedTextAttributes isEqual:textAttributes]) {
+    return _cachedAttributedText;
+  }
+
+  NSMutableAttributedString *attributedText = [NSMutableAttributedString new];
+
+  [attributedText beginEditing];
+
+  for (RCTShadowView *shadowView in self.reactSubviews) {
+    // Special Case: RCTRawTextShadowView
+    if ([shadowView isKindOfClass:[RCTRawTextShadowView class]]) {
+      RCTRawTextShadowView *rawTextShadowView = (RCTRawTextShadowView *)shadowView;
+      NSString *text = rawTextShadowView.text;
+      if (text) {
+        NSAttributedString *rawTextAttributedString =
+          [[NSAttributedString alloc] initWithString:rawTextShadowView.text
+                                          attributes:textAttributes.effectiveTextAttributes];
+        [attributedText appendAttributedString:rawTextAttributedString];
+      }
+      continue;
+    }
+
+    // Special Case: RCTBaseTextShadowView
+    if ([shadowView isKindOfClass:[RCTBaseTextShadowView class]]) {
+      RCTBaseTextShadowView *baseTextShadowView = (RCTBaseTextShadowView *)shadowView;
+      NSAttributedString *baseTextAttributedString =
+        [baseTextShadowView attributedTextWithBaseTextAttributes:textAttributes];
+      [attributedText appendAttributedString:baseTextAttributedString];
+      continue;
+    }
+
+    // Generic Case: Any RCTShadowView
+    NSTextAttachment *attachment = [NSTextAttachment new];
+    NSMutableAttributedString *embeddedShadowViewAttributedString = [NSMutableAttributedString new];
+    [embeddedShadowViewAttributedString beginEditing];
+    [embeddedShadowViewAttributedString appendAttributedString:[NSAttributedString attributedStringWithAttachment:attachment]];
+    [embeddedShadowViewAttributedString addAttribute:RCTBaseTextShadowViewEmbeddedShadowViewAttributeName
+                                               value:shadowView
+                                               range:(NSRange){0, embeddedShadowViewAttributedString.length}];
+    [embeddedShadowViewAttributedString endEditing];
+    [attributedText appendAttributedString:embeddedShadowViewAttributedString];
+  }
+
+  [attributedText endEditing];
+
+  [self clearLayout];
+
+  _cachedAttributedText = [attributedText copy];
+  _cachedTextAttributes = textAttributes;
+
+  return _cachedAttributedText;
+}
+
+- (void)dirtyLayout
+{
+  [super dirtyLayout];
+  _cachedAttributedText = nil;
+  _cachedTextAttributes = nil;
+}
+
+- (void)didUpdateReactSubviews
+{
+  [super didUpdateReactSubviews];
+  [self dirtyLayout];
+}
+
+- (void)didSetProps:(NSArray<NSString *> *)changedProps
+{
+  [super didSetProps:changedProps];
+  [self dirtyLayout];
+}
+
+@end

Libraries/Text/RCTFontAttributesDelegate.h renamed to Libraries/Text/BaseText/RCTBaseTextViewManager.h

@@ -7,8 +7,12 @@
  * of patent rights can be found in the PATENTS file in the same directory.
  */
 
-@protocol RCTFontAttributesDelegate <NSObject>
+#import <React/RCTViewManager.h>
 
-- (void)fontAttributesDidChangeWithFont:(UIFont *)font;
+NS_ASSUME_NONNULL_BEGIN
+
+@interface RCTBaseTextViewManager : RCTViewManager
 
 @end
+
+NS_ASSUME_NONNULL_END

Libraries/Text/BaseText/RCTBaseTextViewManager.m

@@ -0,0 +1,57 @@
+/**
+ * Copyright (c) 2015-present, Facebook, Inc.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree. An additional grant
+ * of patent rights can be found in the PATENTS file in the same directory.
+ */
+
+#import "RCTBaseTextViewManager.h"
+
+@implementation RCTBaseTextViewManager
+
+RCT_EXPORT_MODULE(RCTBaseText)
+
+- (UIView *)view
+{
+  RCTAssert(NO, @"The `-[RCTBaseTextViewManager view]` property must be overridden in subclass.");
+  return nil;
+}
+
+- (RCTShadowView *)shadowView
+{
+  RCTAssert(NO, @"The `-[RCTBaseTextViewManager shadowView]` property must be overridden in subclass.");
+  return nil;
+}
+
+#pragma mark - Text Attributes
+
+// Color
+RCT_REMAP_SHADOW_PROPERTY(color, textAttributes.foregroundColor, UIColor)
+RCT_REMAP_SHADOW_PROPERTY(backgroundColor, textAttributes.backgroundColor, UIColor)
+RCT_REMAP_SHADOW_PROPERTY(opacity, textAttributes.opacity, CGFloat)
+// Font
+RCT_REMAP_SHADOW_PROPERTY(fontFamily, textAttributes.fontFamily, NSString)
+RCT_REMAP_SHADOW_PROPERTY(fontSize, textAttributes.fontSize, CGFloat)
+RCT_REMAP_SHADOW_PROPERTY(fontWeight, textAttributes.fontWeight, NSString)
+RCT_REMAP_SHADOW_PROPERTY(fontStyle, textAttributes.fontStyle, NSString)
+RCT_REMAP_SHADOW_PROPERTY(fontVariant, textAttributes.fontVariant, NSArray)
+RCT_REMAP_SHADOW_PROPERTY(allowFontScaling, textAttributes.allowFontScaling, BOOL)
+RCT_REMAP_SHADOW_PROPERTY(letterSpacing, textAttributes.letterSpacing, CGFloat)
+// Paragraph Styles
+RCT_REMAP_SHADOW_PROPERTY(lineHeight, textAttributes.lineHeight, CGFloat)
+RCT_REMAP_SHADOW_PROPERTY(textAlign, textAttributes.alignment, NSTextAlignment)
+RCT_REMAP_SHADOW_PROPERTY(writingDirection, textAttributes.baseWritingDirection, NSWritingDirection)
+// Decoration
+RCT_REMAP_SHADOW_PROPERTY(textDecorationColor, textAttributes.textDecorationColor, UIColor)
+RCT_REMAP_SHADOW_PROPERTY(textDecorationStyle, textAttributes.textDecorationStyle, NSUnderlineStyle)
+RCT_REMAP_SHADOW_PROPERTY(textDecorationLine, textAttributes.textDecorationLine, RCTTextDecorationLineType)
+// Shadow
+RCT_REMAP_SHADOW_PROPERTY(textShadowOffset, textAttributes.textShadowOffset, CGSize)
+RCT_REMAP_SHADOW_PROPERTY(textShadowRadius, textAttributes.textShadowRadius, CGFloat)
+RCT_REMAP_SHADOW_PROPERTY(textShadowColor, textAttributes.textShadowColor, UIColor)
+// Special
+RCT_REMAP_SHADOW_PROPERTY(isHighlighted, textAttributes.isHighlighted, BOOL)
+
+@end

Libraries/Text/RCTConvert+Text.h

@@ -9,9 +9,13 @@
 
 #import <React/RCTConvert.h>
 
+NS_ASSUME_NONNULL_BEGIN
+
 @interface RCTConvert (Text)
 
-+ (UITextAutocorrectionType)UITextAutocorrectionType:(id)json;
-+ (UITextSpellCheckingType)UITextSpellCheckingType:(id)json;
++ (UITextAutocorrectionType)UITextAutocorrectionType:(nullable id)json;
++ (UITextSpellCheckingType)UITextSpellCheckingType:(nullable id)json;
 
 @end
+
+NS_ASSUME_NONNULL_END