iOS: Exposes the RCTFont size overrides so unit tests can use the same values

Summary:
`RCTFontTests` test in RNTester is broken if the target deployment is <= OS 8.2. This is because RCTFont.mm overrides the OS-defined values, but the override is only visible to RCTFont.mm internals. As the result, when the Unit test tries to create UIFont of the "same" weight, it got a different font - most likely due to internal floating rounding errors.

To mitigate, code that wants to test out internals of RCTFont should import RCTFontConstantsOverride.h

Reviewed By: mmmulani

Differential Revision: D7900954

fbshipit-source-id: e5814ef059a8afdfb5205ca1af46c41b3cfd4318

Author: fkgozali

RNTester/RNTesterUnitTests/RCTFontTests.m

@@ -10,6 +10,7 @@
 #import <XCTest/XCTest.h>
 
 #import <React/RCTFont.h>
+#import <React/RCTFontConstantsOverride.h>
 
 @interface RCTFontTests : XCTestCase
 

React/React.xcodeproj/project.pbxproj

@@ -1147,6 +1147,8 @@
 		59EDBCC61FDF4E55003573DE /* (null) in Copy Headers */ = {isa = PBXBuildFile; };
 		59EDBCC71FDF4E55003573DE /* RCTScrollView.h in Copy Headers */ = {isa = PBXBuildFile; fileRef = 59EDBCA31FDF4E0C003573DE /* RCTScrollView.h */; };
 		59EDBCC81FDF4E55003573DE /* RCTScrollViewManager.h in Copy Headers */ = {isa = PBXBuildFile; fileRef = 59EDBCA51FDF4E0C003573DE /* RCTScrollViewManager.h */; };
+		5C70426020A1004800FBEEF7 /* RCTFontConstantsOverride.h in Headers */ = {isa = PBXBuildFile; fileRef = 5C70425F20A1004800FBEEF7 /* RCTFontConstantsOverride.h */; };
+		5C70426120A1022C00FBEEF7 /* RCTFontConstantsOverride.h in Copy Headers */ = {isa = PBXBuildFile; fileRef = 5C70425F20A1004800FBEEF7 /* RCTFontConstantsOverride.h */; };
 		5CE2080220772F7D009A43B3 /* YGConfig.cpp in Sources */ = {isa = PBXBuildFile; fileRef = 5CE2080020772F7C009A43B3 /* YGConfig.cpp */; };
 		5CE2080320772F7D009A43B3 /* YGConfig.h in Headers */ = {isa = PBXBuildFile; fileRef = 5CE2080120772F7C009A43B3 /* YGConfig.h */; };
 		657734841EE834C900A0E9EA /* RCTInspectorDevServerHelper.h in Headers */ = {isa = PBXBuildFile; fileRef = 657734821EE834C900A0E9EA /* RCTInspectorDevServerHelper.h */; };
@@ -1599,6 +1601,7 @@
 			dstPath = include/React;
 			dstSubfolderSpec = 16;
 			files = (
+				5C70426120A1022C00FBEEF7 /* RCTFontConstantsOverride.h in Copy Headers */,
 				39C50FF92046EACF00CEE534 /* RCTVersion.h in Copy Headers */,
 				591F78DE202ADB8F004A668C /* RCTLayout.h in Copy Headers */,
 				59EDBCBD1FDF4E43003573DE /* RCTScrollableProtocol.h in Copy Headers */,
@@ -2240,6 +2243,7 @@
 		59EDBCA41FDF4E0C003573DE /* RCTScrollView.m */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.objc; path = RCTScrollView.m; sourceTree = "<group>"; };
 		59EDBCA51FDF4E0C003573DE /* RCTScrollViewManager.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = RCTScrollViewManager.h; sourceTree = "<group>"; };
 		59EDBCA61FDF4E0C003573DE /* RCTScrollViewManager.m */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.objc; path = RCTScrollViewManager.m; sourceTree = "<group>"; };
+		5C70425F20A1004800FBEEF7 /* RCTFontConstantsOverride.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = RCTFontConstantsOverride.h; sourceTree = "<group>"; };
 		5CE2080020772F7C009A43B3 /* YGConfig.cpp */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.cpp; path = YGConfig.cpp; sourceTree = "<group>"; };
 		5CE2080120772F7C009A43B3 /* YGConfig.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = YGConfig.h; sourceTree = "<group>"; };
 		657734821EE834C900A0E9EA /* RCTInspectorDevServerHelper.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = RCTInspectorDevServerHelper.h; sourceTree = "<group>"; };
@@ -2561,6 +2565,7 @@
 		13B07FF31A6947C200A75B9A /* Views */ = {
 			isa = PBXGroup;
 			children = (
+				5C70425F20A1004800FBEEF7 /* RCTFontConstantsOverride.h */,
 				B95154301D1B34B200FE7B80 /* RCTActivityIndicatorView.h */,
 				B95154311D1B34B200FE7B80 /* RCTActivityIndicatorView.m */,
 				13B080181A69489C00A75B9A /* RCTActivityIndicatorViewManager.h */,
@@ -3568,6 +3573,7 @@
 				3D80DA621DF820620028D040 /* RCTAutoInsetsProtocol.h in Headers */,
 				C60128AB1F3D1258009DF9FF /* RCTCxxConvert.h in Headers */,
 				59EDBCAD1FDF4E0C003573DE /* RCTScrollContentView.h in Headers */,
+				5C70426020A1004800FBEEF7 /* RCTFontConstantsOverride.h in Headers */,
 				59EDBCA71FDF4E0C003573DE /* RCTScrollableProtocol.h in Headers */,
 				591F78DC202ADB22004A668C /* RCTLayout.h in Headers */,
 				5CE2080320772F7D009A43B3 /* YGConfig.h in Headers */,

React/Views/RCTFont.mm

@@ -7,31 +7,13 @@
 
 #import "RCTAssert.h"
 #import "RCTFont.h"
+#import "RCTFontConstantsOverride.h"
 #import "RCTLog.h"
 
 #import <CoreText/CoreText.h>
 
 #import <mutex>
 
-#if !defined(__IPHONE_8_2) || __IPHONE_OS_VERSION_MIN_REQUIRED < __IPHONE_8_2
-
-// These constants are defined in iPhone SDK 8.2, but the app cannot run on
-// iOS < 8.2 unless we redefine them here. If you target iOS 8.2 or above
-// as a base target, the standard constants will be used instead.
-// These constants can only be removed when React Native drops iOS8 support.
-
-#define UIFontWeightUltraLight -0.8
-#define UIFontWeightThin -0.6
-#define UIFontWeightLight -0.4
-#define UIFontWeightRegular 0
-#define UIFontWeightMedium 0.23
-#define UIFontWeightSemibold 0.3
-#define UIFontWeightBold 0.4
-#define UIFontWeightHeavy 0.56
-#define UIFontWeightBlack 0.62
-
-#endif
-
 typedef CGFloat RCTFontWeight;
 static RCTFontWeight weightOfFont(UIFont *font)
 {

React/Views/RCTFontConstantsOverride.h

@@ -0,0 +1,29 @@
+/**
+ * Copyright (c) 2015-present, Facebook, Inc.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+// NOTE: Include this header file to ensure consistency of the constants defined here.
+// The values are the ones used in RCTFont.mm.
+// Example: import it for testing RCTFont internals in a unit test.
+
+#if !defined(__IPHONE_8_2) || __IPHONE_OS_VERSION_MIN_REQUIRED < __IPHONE_8_2
+
+// These constants are defined in iPhone SDK 8.2, but the app cannot run on
+// iOS < 8.2 unless we redefine them here. If you target iOS 8.2 or above
+// as a base target, the standard constants will be used instead.
+// These constants can only be removed when React Native drops iOS8 support.
+
+#define UIFontWeightUltraLight -0.8
+#define UIFontWeightThin -0.6
+#define UIFontWeightLight -0.4
+#define UIFontWeightRegular 0
+#define UIFontWeightMedium 0.23
+#define UIFontWeightSemibold 0.3
+#define UIFontWeightBold 0.4
+#define UIFontWeightHeavy 0.56
+#define UIFontWeightBlack 0.62
+
+#endif