Add letterSpacing style property for Text

Summary:
Fixes #457
Closes https://github.com/facebook/react-native/pull/482
Github Author: Vladimir Kurchatkin <vladimir.kurchatkin@gmail.com>

Test Plan: Imported from GitHub, without a `Test Plan:` line.

Examples/UIExplorer/TextExample.ios.js

@@ -218,6 +218,26 @@ exports.examples = [
       </View>
     );
   },
+}, {
+  title: 'Letter Spacing',
+  render: function() {
+    return (
+      <View>
+        <Text style={{letterSpacing: 0}}>
+          letterSpacing = 0
+        </Text>
+        <Text style={{letterSpacing: 2, marginTop: 5}}>
+          letterSpacing = 2
+        </Text>
+        <Text style={{letterSpacing: 9, marginTop: 5}}>
+          letterSpacing = 9
+        </Text>
+        <Text style={{letterSpacing: -1, marginTop: 5}}>
+          letterSpacing = -1
+        </Text>
+      </View>
+    );
+  },
 }, {
   title: 'Spaces',
   render: function() {

Examples/UIExplorer/UIExplorerTests/UIExplorerTests.m

@@ -88,35 +88,19 @@
   XCTAssertTrue(foundElement, @"Cound't find element with '<View>' text in %d seconds", TIMEOUT_SECONDS);
 }
 
-- (void)testViewExampleSnapshot
-{
-  [_runner runTest:_cmd module:@"ViewExample"];
+#define RCT_SNAPSHOT_TEST(name, reRecord) \
+- (void)test##name##Snapshot              \
+{                                         \
+  _runner.recordMode |= reRecord;         \
+  [_runner runTest:_cmd module:@#name];   \
 }
 
-- (void)testLayoutExampleSnapshot
-{
-  [_runner runTest:_cmd module:@"LayoutExample"];
-}
-
-- (void)testTextExampleSnapshot
-{
-  [_runner runTest:_cmd module:@"TextExample"];
-}
-
-- (void)testSwitchExampleSnapshot
-{
-  [_runner runTest:_cmd module:@"SwitchExample"];
-}
-
-- (void)testSliderExampleSnapshot
-{
-  [_runner runTest:_cmd module:@"SliderExample"];
-}
-
-- (void)testTabBarExampleSnapshot
-{
-  [_runner runTest:_cmd module:@"TabBarExample"];
-}
+RCT_SNAPSHOT_TEST(ViewExample, NO)
+RCT_SNAPSHOT_TEST(LayoutExample, NO)
+RCT_SNAPSHOT_TEST(TextExample, NO)
+RCT_SNAPSHOT_TEST(SwitchExample, NO)
+RCT_SNAPSHOT_TEST(SliderExample, NO)
+RCT_SNAPSHOT_TEST(TabBarExample, NO)
 
 // Make sure this test runs last
 - (void)testZZZ_NotInRecordMode

Libraries/Text/RCTShadowText.h

@@ -22,6 +22,7 @@ extern NSString *const RCTReactTagAttributeName;
 @property (nonatomic, copy) NSString *fontWeight;
 @property (nonatomic, copy) NSString *fontStyle;
 @property (nonatomic, assign) BOOL isHighlighted;
+@property (nonatomic, assign) CGFloat letterSpacing;
 @property (nonatomic, assign) CGFloat lineHeight;
 @property (nonatomic, assign) NSUInteger maximumNumberOfLines;
 @property (nonatomic, assign) CGSize shadowOffset;
@@ -30,6 +31,7 @@ extern NSString *const RCTReactTagAttributeName;
 // Not exposed to JS
 @property (nonatomic, strong) UIFont *font;
 @property (nonatomic, assign) NSLineBreakMode truncationMode;
+@property (nonatomic, assign) CGFloat effectiveLetterSpacing;
 
 @property (nonatomic, copy, readonly) NSAttributedString *attributedString;
 @property (nonatomic, strong, readonly) NSLayoutManager *layoutManager;

Libraries/Text/RCTShadowText.m

@@ -40,11 +40,15 @@ static css_dim_t RCTMeasure(void *context, float width)
 
   css_dim_t result;
   result.dimensions[CSS_WIDTH] = RCTCeilPixelValue(computedSize.width);
+  if (shadowText.effectiveLetterSpacing < 0) {
+    result.dimensions[CSS_WIDTH] -= shadowText.effectiveLetterSpacing;
+  }
   result.dimensions[CSS_HEIGHT] = RCTCeilPixelValue(computedSize.height);
   return result;
 }
 
-@implementation RCTShadowText {
+@implementation RCTShadowText
+{
   NSLayoutManager *_layoutManager;
   NSTextContainer *_textContainer;
   NSAttributedString *_cachedAttributedString;
@@ -55,6 +59,7 @@ static css_dim_t RCTMeasure(void *context, float width)
 {
   if ((self = [super init])) {
     _fontSize = NAN;
+    _letterSpacing = NAN;
     _isHighlighted = NO;
 
     _textContainer = [[NSTextContainer alloc] init];
@@ -71,22 +76,24 @@ static css_dim_t RCTMeasure(void *context, float width)
 - (NSAttributedString *)attributedString
 {
   return [self _attributedStringWithFontFamily:nil
-                                      fontSize:0
+                                      fontSize:nil
                                     fontWeight:nil
-                                     fontStyle:nil];
+                                     fontStyle:nil
+                                 letterSpacing:nil];
 }
 
 - (NSAttributedString *)_attributedStringWithFontFamily:(NSString *)fontFamily
-                                               fontSize:(CGFloat)fontSize
+                                               fontSize:(NSNumber *)fontSize
                                              fontWeight:(NSString *)fontWeight
                                               fontStyle:(NSString *)fontStyle
+                                          letterSpacing:(NSNumber *)letterSpacing
 {
   if (![self isTextDirty] && _cachedAttributedString) {
     return _cachedAttributedString;
   }
 
   if (_fontSize && !isnan(_fontSize)) {
-    fontSize = _fontSize;
+    fontSize = @(_fontSize);
   }
   if (_fontWeight) {
     fontWeight = _fontWeight;
@@ -97,12 +104,17 @@ static css_dim_t RCTMeasure(void *context, float width)
   if (_fontFamily) {
     fontFamily = _fontFamily;
   }
+  if (!isnan(_letterSpacing)) {
+    letterSpacing = @(_letterSpacing);
+  }
+
+  _effectiveLetterSpacing = letterSpacing.doubleValue;
 
   NSMutableAttributedString *attributedString = [[NSMutableAttributedString alloc] init];
   for (RCTShadowView *child in [self reactSubviews]) {
     if ([child isKindOfClass:[RCTShadowText class]]) {
       RCTShadowText *shadowText = (RCTShadowText *)child;
-      [attributedString appendAttributedString:[shadowText _attributedStringWithFontFamily:fontFamily fontSize:fontSize fontWeight:fontWeight fontStyle:fontStyle]];
+      [attributedString appendAttributedString:[shadowText _attributedStringWithFontFamily:fontFamily fontSize:fontSize fontWeight:fontWeight fontStyle:fontStyle letterSpacing:letterSpacing]];
     } else if ([child isKindOfClass:[RCTShadowRawText class]]) {
       RCTShadowRawText *shadowRawText = (RCTShadowRawText *)child;
       [attributedString appendAttributedString:[[NSAttributedString alloc] initWithString:[shadowRawText text] ?: @""]];
@@ -123,8 +135,9 @@ static css_dim_t RCTMeasure(void *context, float width)
     [self _addAttribute:NSBackgroundColorAttributeName withValue:self.textBackgroundColor toAttributedString:attributedString];
   }
 
-  _font = [RCTConvert UIFont:nil withFamily:fontFamily size:@(fontSize) weight:fontWeight style:fontStyle];
+  _font = [RCTConvert UIFont:nil withFamily:fontFamily size:fontSize weight:fontWeight style:fontStyle];
   [self _addAttribute:NSFontAttributeName withValue:_font toAttributedString:attributedString];
+  [self _addAttribute:NSKernAttributeName withValue:letterSpacing toAttributedString:attributedString];
   [self _addAttribute:RCTReactTagAttributeName withValue:self.reactTag toAttributedString:attributedString];
   [self _setParagraphStyleOnAttributedString:attributedString];
 
@@ -143,7 +156,7 @@ static css_dim_t RCTMeasure(void *context, float width)
 - (void)_addAttribute:(NSString *)attribute withValue:(id)attributeValue toAttributedString:(NSMutableAttributedString *)attributedString
 {
   [attributedString enumerateAttribute:attribute inRange:NSMakeRange(0, [attributedString length]) options:0 usingBlock:^(id value, NSRange range, BOOL *stop) {
-    if (!value) {
+    if (!value && attributeValue) {
       [attributedString addAttribute:attribute value:attributeValue range:range];
     }
   }];
@@ -223,6 +236,7 @@ RCT_TEXT_PROPERTY(Color, _color, UIColor *);
 RCT_TEXT_PROPERTY(FontFamily, _fontFamily, NSString *);
 RCT_TEXT_PROPERTY(FontSize, _fontSize, CGFloat);
 RCT_TEXT_PROPERTY(FontWeight, _fontWeight, NSString *);
+RCT_TEXT_PROPERTY(LetterSpacing, _letterSpacing, CGFloat);
 RCT_TEXT_PROPERTY(LineHeight, _lineHeight, CGFloat);
 RCT_TEXT_PROPERTY(ShadowOffset, _shadowOffset, CGSize);
 RCT_TEXT_PROPERTY(TextAlign, _textAlign, NSTextAlignment);

Libraries/Text/RCTText.h

@@ -14,7 +14,6 @@
 @property (nonatomic, strong) NSLayoutManager *layoutManager;
 @property (nonatomic, strong) NSTextContainer *textContainer;
 @property (nonatomic, copy) NSAttributedString *attributedText;
-
 @property (nonatomic, assign) UIEdgeInsets contentInset;
 
 @end

Libraries/Text/RCTTextManager.m

@@ -45,6 +45,7 @@ RCT_EXPORT_SHADOW_PROPERTY(fontSize, CGFloat)
 RCT_EXPORT_SHADOW_PROPERTY(fontWeight, NSString)
 RCT_EXPORT_SHADOW_PROPERTY(fontStyle, NSString)
 RCT_EXPORT_SHADOW_PROPERTY(isHighlighted, BOOL)
+RCT_EXPORT_SHADOW_PROPERTY(letterSpacing, CGFloat)
 RCT_EXPORT_SHADOW_PROPERTY(lineHeight, CGFloat)
 RCT_EXPORT_SHADOW_PROPERTY(maximumNumberOfLines, NSInteger)
 RCT_EXPORT_SHADOW_PROPERTY(shadowOffset, CGSize)

Libraries/Text/TextStylePropTypes.js

@@ -32,6 +32,7 @@ var TextStylePropTypes = Object.assign(Object.create(ViewStylePropTypes), {
   writingDirection: ReactPropTypes.oneOf(
     ['auto' /*default*/, 'ltr', 'rtl']
   ),
+  letterSpacing: ReactPropTypes.number,
 });
 
 // Text doesn't support padding correctly (#4841912)