[Text] RCTConvert uses fontDescriptor of System font or given fonts.

 * System font + weight -> It uses fontDescriptor to generate font.
 * Other font -> uses fontDescriptor to getnere font.
 * Other font + weight/fontName -> It uses familyName to generate font.

It looks like iOS doesn't support changing weight dynamically.

Author: dalinaum

Examples/UIExplorer/UIExplorerIntegrationTests/ReferenceImages/Examples-UIExplorer-UIExplorerApp.ios/testLayoutExampleSnapshot_1@2x.png

@@ -41,8 +41,7 @@ - (void)DISABLED_testWeight // task #7118691
 - (void)testSize
 {
   {
-    UIFont *expected =
-      [UIFont fontWithName:[UIFont systemFontOfSize:18.5].fontName size:18.5];
+    UIFont *expected = [UIFont systemFontOfSize:18.5];
     UIFont *result = [RCTConvert UIFont:@{@"fontSize": @18.5}];
     RCTAssertEqualFonts(expected, result);
   }
@@ -69,33 +68,20 @@ - (void)testFamily
 
 - (void)testStyle
 {
-  NSString *systemFontName = [UIFont systemFontOfSize:14].fontName; 
   {
-    UIFont *bestMatch = [UIFont fontWithName:systemFontName size: 14];
-    CGFloat closestWeight = INFINITY;
-
-    for (NSString *name in [UIFont fontNamesForFamilyName:systemFontName]) {
-      UIFont *match = [UIFont fontWithName:name size:14];
-      NSDictionary *traits = [match.fontDescriptor objectForKey:UIFontDescriptorTraitsAttribute];
-      UIFontDescriptorSymbolicTraits symbolicTraits =
-        [traits[UIFontSymbolicTrait] unsignedIntValue];
-      BOOL isItalic = (symbolicTraits & UIFontDescriptorTraitItalic) != 0;
-      BOOL isCondensed = (symbolicTraits & UIFontDescriptorTraitCondensed) != 0;
-      CGFloat weightOfFont = [traits[UIFontWeightTrait] doubleValue];
-
-      if (isItalic && !isCondensed) {
-        if (ABS(weightOfFont) < ABS(closestWeight)) {
-          bestMatch = match;
-          closestWeight = weightOfFont;
-        }
-      }
-    }
-    UIFont *expected = [UIFont fontWithName:bestMatch.fontName size:14];
+    UIFont *font = [UIFont systemFontOfSize:14];
+    UIFontDescriptor *fontDescriptor = [font fontDescriptor];
+    UIFontDescriptorSymbolicTraits symbolicTraits =
+      fontDescriptor.symbolicTraits;
+    symbolicTraits |= UIFontDescriptorTraitItalic;
+    fontDescriptor =
+      [fontDescriptor fontDescriptorWithSymbolicTraits:symbolicTraits];
+    UIFont *expected = [UIFont fontWithDescriptor:fontDescriptor size:14];
     UIFont *result = [RCTConvert UIFont:@{@"fontStyle": @"italic"}];
     RCTAssertEqualFonts(expected, result);
   }
   {
-    UIFont *expected = [UIFont fontWithName:systemFontName size:14];
+    UIFont *expected = [UIFont systemFontOfSize:14];
     UIFont *result = [RCTConvert UIFont:@{@"fontStyle": @"normal"}];
     RCTAssertEqualFonts(expected, result);
   }

Examples/UIExplorer/UIExplorerIntegrationTests/ReferenceImages/Examples-UIExplorer-UIExplorerApp.ios/testSliderExampleSnapshot_1@2x.png

@@ -759,10 +759,54 @@ + (UIFont *)UIFont:(UIFont *)font withFamily:(id)family
 
   if ([[self NSString:family] isEqualToString:RCTDefaultFontFamily] ||
       (!family && !font)) {
-    font = [UIFont systemFontOfSize:fontSize];
+    if (font) {
+      fontSize = font.pointSize ?: RCTDefaultFontSize;
+      fontWeight = RCTWeightOfFont(font);
+      isItalic = RCTFontIsItalic(font);
+    }
+    fontSize = [self CGFloat:size] ?: fontSize;
+    fontWeight = [self RCTFontWeight:weight] ?: fontWeight;
+
+    if (weight) {
+      font = [UIFont systemFontOfSize:fontSize weight:fontWeight];
+    } else {
+      font = [UIFont systemFontOfSize:fontSize];
+    }
+
+    UIFontDescriptor *fontDescriptor = [font fontDescriptor];
+    UIFontDescriptorSymbolicTraits symbolicTraits =
+      fontDescriptor.symbolicTraits;
+    if (style) {
+      isItalic = [self RCTFontStyle:style];
+    }
+    if (isItalic) {
+      symbolicTraits |= UIFontDescriptorTraitItalic;
+      fontDescriptor =
+        [fontDescriptor fontDescriptorWithSymbolicTraits:symbolicTraits];
+    }
+    return [UIFont fontWithDescriptor:fontDescriptor size:fontSize];
   }
 
   if (font) {
+    if (!family && !weight) {
+      fontSize = font.pointSize ?: RCTDefaultFontSize;
+      fontSize = [self CGFloat:size] ?: fontSize;
+
+      UIFontDescriptor *fontDescriptor = [font fontDescriptor];
+      UIFontDescriptorSymbolicTraits symbolicTraits =
+        fontDescriptor.symbolicTraits;
+
+      if (style) {
+        isItalic = [self RCTFontStyle:style];
+      }
+      if (italic) {
+        symbolicTraits |= UIFontDescriptorTraitItalic;
+        fontDescriptor =
+          [fontDescriptor fontDescriptorWithSymbolicTraits:symbolicTraits];
+      }
+      return [UIFont fontWithDescriptor:fontDescriptor size:fontSize];
+    }
+
     familyName = font.familyName ?: RCTDefaultFontFamily;
     fontSize = font.pointSize ?: RCTDefaultFontSize;
     fontWeight = RCTWeightOfFont(font);