[Text] Get the system font instead of Helvetica programmatically and add a virtual fontName called "System"

Examples/UIExplorer/UIExplorerUnitTests/RCTConvert_UIFontTests.m

@@ -41,7 +41,7 @@ - (void)DISABLED_testWeight // task #7118691
 - (void)testSize
 {
   {
-    UIFont *expected = [UIFont fontWithName:@"HelveticaNeue" size:18.5];
+    UIFont *expected = [UIFont systemFontOfSize:18.5];
     UIFont *result = [RCTConvert UIFont:@{@"fontSize": @18.5}];
     RCTAssertEqualFonts(expected, result);
   }
@@ -69,12 +69,19 @@ - (void)testFamily
 - (void)testStyle
 {
   {
-    UIFont *expected = [UIFont fontWithName:@"HelveticaNeue-Italic" 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:@"HelveticaNeue" size:14];
+    UIFont *expected = [UIFont systemFontOfSize:14];
     UIFont *result = [RCTConvert UIFont:@{@"fontStyle": @"normal"}];
     RCTAssertEqualFonts(expected, result);
   }

Libraries/Text/RCTTextView.m

@@ -222,7 +222,7 @@ - (BOOL)canBecomeFirstResponder
 
 - (UIFont *)defaultPlaceholderFont
 {
-  return [UIFont fontWithName:@"Helvetica" size:17];
+  return [UIFont systemFontOfSize:17];
 }
 
 - (UIColor *)defaultPlaceholderTextColor

React/Base/RCTConvert.m

@@ -746,7 +746,7 @@ + (UIFont *)UIFont:(UIFont *)font withFamily:(id)family
               size:(id)size weight:(id)weight style:(id)style
 {
   // Defaults
-  NSString *const RCTDefaultFontFamily = @"Helvetica Neue";
+  NSString *const RCTDefaultFontFamily = @"System";
   const RCTFontWeight RCTDefaultFontWeight = UIFontWeightRegular;
   const CGFloat RCTDefaultFontSize = 14;
 
@@ -757,7 +757,59 @@ + (UIFont *)UIFont:(UIFont *)font withFamily:(id)family
   BOOL isItalic = NO;
   BOOL isCondensed = NO;
 
+  if ([[self NSString:family] isEqualToString:RCTDefaultFontFamily] ||
+      (!family && !font)) {
+    if (font) {
+      fontSize = font.pointSize ?: RCTDefaultFontSize;
+      fontWeight = RCTWeightOfFont(font);
+      isItalic = RCTFontIsItalic(font);
+    }
+
+    fontSize = [self CGFloat:size] ?: fontSize;
+
+    if (weight) {
+      fontWeight = [self RCTFontWeight:weight];
+    }
+
+    font = [UIFont systemFontOfSize:fontSize];
+
+    if (ABS(fontWeight - RCTDefaultFontWeight) <  0.01) {
+      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 (isItalic) {
+        symbolicTraits |= UIFontDescriptorTraitItalic;
+        fontDescriptor =
+          [fontDescriptor fontDescriptorWithSymbolicTraits:symbolicTraits];
+      }
+      return [UIFont fontWithDescriptor:fontDescriptor size:fontSize];
+    }
+
     familyName = font.familyName ?: RCTDefaultFontFamily;
     fontSize = font.pointSize ?: RCTDefaultFontSize;
     fontWeight = RCTWeightOfFont(font);