Avoid crash in NSOrthography category method

platform/darwin/src/NSString+MGLAdditions.h

@@ -22,14 +22,14 @@ NS_ASSUME_NONNULL_BEGIN
 
 /**
  Returns a transliterated representation of the receiver using the specified
- script. If transliteration fails, the receiver will be returned.
+ script. If transliteration fails or script is nil, the receiver will be returned.
 
  Only supports scripts for languages used by Mapbox Streets.
 
  @param script The four-letter code representing the name of the script, as
     specified by ISO 15924.
  */
-- (NSString *)mgl_stringByTransliteratingIntoScript:(NSString *)script;
+- (NSString *)mgl_stringByTransliteratingIntoScript:(nullable NSString *)script;
 
 @end
 

platform/darwin/src/NSString+MGLAdditions.m

@@ -40,7 +40,7 @@ - (NSString *)mgl_titleCasedStringWithLocale:(NSLocale *)locale {
     return string;
 }
 
-- (NSString *)mgl_stringByTransliteratingIntoScript:(NSString *)script {
+- (NSString *)mgl_stringByTransliteratingIntoScript:(nullable NSString *)script {
     NSMutableString *string = self.mutableCopy;
     NSStringTransform transform;
     if ([script isEqualToString:@"Latn"]) {

platform/darwin/test/MGLNSStringAdditionsTests.m

@@ -84,6 +84,8 @@ - (void)testTransliteratedString {
     XCTAssertEqualObjects([@"ロンドン" mgl_stringByTransliteratingIntoScript:@"Jpan"], @"ロンドン");
     XCTAssertEqualObjects([@"ロンドン" mgl_stringByTransliteratingIntoScript:@"Kore"], @"론돈");
     XCTAssertEqualObjects([@"ロンドン" mgl_stringByTransliteratingIntoScript:@"Fake"], @"ロンドン");
+
+    XCTAssertEqualObjects([@"" mgl_stringByTransliteratingIntoScript:nil], @"");
 }
 
 @end

platform/ios/CHANGELOG.md

@@ -8,6 +8,7 @@ Mapbox welcomes participation and contributions from everyone. Please read [CONT
 
 * Fixed a CocoaPods warning when integrating this SDK and the Mapbox Navigation SDK for iOS into the same application. ([#549](https://github.com/mapbox/mapbox-gl-native-ios/pull/549))
 * Fixed an issue where offline packs were not invalidated before being deallocated, resulting in a crash. ([#620](https://github.com/mapbox/mapbox-gl-native-ios/pull/620))
+* Fixed a crash in `-[NSOrthography mgl_dominantScriptForMapboxStreetsLanguage]`. ([#619](https://github.com/mapbox/mapbox-gl-native-ios/pull/619))
 
 ## 6.3.0 - November 10, 2020
 

platform/ios/src/MGLMapAccessibilityElement.mm

@@ -49,8 +49,11 @@ - (instancetype)initWithAccessibilityContainer:(id)container feature:(id<MGLFeat
         _feature = feature;
 
         NSString *languageCode = [MGLVectorTileSource preferredMapboxStreetsLanguage];
-        NSString *nameAttribute = [NSString stringWithFormat:@"name_%@", languageCode];
-        NSString *name = [feature attributeForKey:nameAttribute];
+        NSString *name;
+        if (languageCode != nil) {
+            NSString *nameAttribute = [NSString stringWithFormat:@"name_%@", languageCode];
+            name = [feature attributeForKey:nameAttribute];
+        }
 
         NSString *dominantScript;
         if (name == nil && [feature attributeForKey:@"name"] != nil) {
@@ -62,7 +65,7 @@ - (instancetype)initWithAccessibilityContainer:(id)container feature:(id<MGLFeat
         // may be in the local language, which may be written in another script.
         // Attempt to transform to the script of the preferred language, keeping
         // the original string if no transform exists or if transformation fails.
-        if (!dominantScript) {
+        if (dominantScript == nil && languageCode != nil) {
             dominantScript = [NSOrthography mgl_dominantScriptForMapboxStreetsLanguage:languageCode];
         }
         name = [name mgl_stringByTransliteratingIntoScript:dominantScript];
@@ -88,7 +91,7 @@ - (instancetype)initWithAccessibilityContainer:(id)container feature:(id<MGLFeat
         // Announce the kind of place or POI.
         NSString *languageCode = [MGLVectorTileSource preferredMapboxStreetsLanguage];
         NSString *categoryAttribute = [NSString stringWithFormat:@"category_%@", languageCode];
-        if (attributes[categoryAttribute]) {
+        if (languageCode != nil && attributes[categoryAttribute]) {
             [facts addObject:attributes[categoryAttribute]];
         } else if (attributes[@"type"]) {
             // FIXME: Unfortunately, these types aren’t a closed set that can be

platform/ios/src/NSOrthography+MGLAdditions.m

@@ -3,6 +3,10 @@
 @implementation NSOrthography (MGLAdditions)
 
 + (NSString *)mgl_dominantScriptForMapboxStreetsLanguage:(NSString *)language {
+    if (language == nil) {
+        return nil;
+    }
+
     if (@available(iOS 11.0, *)) {
         NSLocale *locale = [NSLocale localeWithLocaleIdentifier:language];
         NSOrthography *orthography = [NSOrthography defaultOrthographyForLanguage:locale.localeIdentifier];

platform/ios/test/MGLNSOrthographyAdditionsTests.m

@@ -16,4 +16,8 @@ - (void)testStreetsLanguages {
     }
 }
 
+- (void)testDominantScriptWhenLanguageIsNil {
+    XCTAssertNil([NSOrthography mgl_dominantScriptForMapboxStreetsLanguage:nil]);
+}
+
 @end