Provide forceRTL for LTR language to test

Summary:
1. Provide forceRTL function for developer to test RTL layout in LTR language bundle in I18nUtil and expose it in I18nManager.
2. Rename `allowRTL` and `setAllowRTL` functions

Reviewed By: fkgozali

Differential Revision: D3663693

fbshipit-source-id: 3db13a44c069ae73d1728c211306422db5dd8122

Libraries/Utilities/I18nManager.js

@@ -14,11 +14,13 @@
 type I18nManagerStatus = {
   isRTL: boolean,
   allowRTL: (allowRTL: boolean) => {},
+  forceRTL: (forceRTL: boolean) => {},
 };
 
 const I18nManager : I18nManagerStatus = require('NativeModules').I18nManager || {
   isRTL: false,
   allowRTL: () => {},
+  forceRTL: () => {},
 };
 
 module.exports = I18nManager;

React/Modules/RCTI18nManager.m

@@ -16,7 +16,12 @@ RCT_EXPORT_MODULE()
 
 RCT_EXPORT_METHOD(allowRTL:(BOOL)value)
 {
-  [[RCTI18nUtil sharedInstance] setAllowRTL:value];
+  [[RCTI18nUtil sharedInstance] allowRTL:value];
+}
+
+RCT_EXPORT_METHOD(forceRTL:(BOOL)value)
+{
+  [[RCTI18nUtil sharedInstance] forceRTL:value];
 }
 
 - (NSDictionary *)constantsToExport

React/Modules/RCTI18nUtil.h

@@ -18,8 +18,10 @@
 @interface RCTI18nUtil : NSObject
 
 - (BOOL)isRTL;
-- (BOOL)allowRTL;
-- (void)setAllowRTL:(BOOL)value;
+- (BOOL)isRTLAllowed;
+- (void)allowRTL:(BOOL)value;
+- (BOOL)isRTLForced;
+- (void)forceRTL:(BOOL)value;
 + (id)sharedInstance;
 
 @end

React/Modules/RCTI18nUtil.m

@@ -22,29 +22,57 @@
    return sharedRCTI18nUtilInstance;
 }
 
-// If current using language is RTL language and meanwhile set allowRTL on the JS side,
-// the RN app will automatically have a RTL layout.
+/**
+ * Check if the app is currently running on an RTL locale.
+ * This only happens when the app:
+ * - is forcing RTL layout, regardless of the active language (for development purpose)
+ * - allows RTL layout when using RTL locale
+ */
 - (BOOL)isRTL
 {
-  if ([self allowRTL] && [self isApplicationPreferredLanguageRTL]) {
+  if ([self isRTLForced]) {
+    return YES;
+  }
+  if ([self isRTLAllowed] && [self isApplicationPreferredLanguageRTL]) {
     return YES;
   }
   return NO;
 }
 
-- (BOOL)allowRTL
+/**
+ * Should be used very early during app start up
+ * Before the bridge is initialized
+ */
+- (BOOL)isRTLAllowed
 {
   BOOL rtlStatus = [[NSUserDefaults standardUserDefaults]
                             boolForKey:@"RCTI18nUtil_allowRTL"];
   return rtlStatus;
 }
 
-- (void)setAllowRTL:(BOOL)rtlStatus
+- (void)allowRTL:(BOOL)rtlStatus
 {
   [[NSUserDefaults standardUserDefaults] setBool:rtlStatus forKey:@"RCTI18nUtil_allowRTL"];
   [[NSUserDefaults standardUserDefaults] synchronize];
 }
 
+/**
+ * Could be used to test RTL layout with English
+ * Used for development and testing purpose
+ */
+- (BOOL)isRTLForced
+{
+  BOOL rtlStatus = [[NSUserDefaults standardUserDefaults]
+                            boolForKey:@"RCTI18nUtil_forceRTL"];
+  return rtlStatus;
+}
+
+- (void)forceRTL:(BOOL)rtlStatus
+{
+  [[NSUserDefaults standardUserDefaults] setBool:rtlStatus forKey:@"RCTI18nUtil_forceRTL"];
+  [[NSUserDefaults standardUserDefaults] synchronize];
+}
+
 // Check if the current device language is RTL
 - (BOOL)isDevicePreferredLanguageRTL
 {