[iOS] Set application root as asset root

As of #2746, we no longer bundle any styles with the SDK, so the asset: URL scheme is unused. Instead, point asset: to the application root for developer convenience and consistency with the Android and default asset roots. Also fixed an issue that prevented relative URLs from being treated as asset: URLs.

Fixes #1208, fixes #3050.

CHANGELOG.md

@@ -27,6 +27,7 @@ Known issues:
 - The `styleID` property has been removed from MGLMapView. Instead, set the `styleURL` property to an NSURL in the form `mapbox://styles/STYLE_ID`. If you previously set the style ID in Interface Builder’s Attributes inspector, delete the `styleID` entry from the User Defined Runtime Attributes section of the Identity inspector, then set the new “Style URL” inspectable to a value in the form `mapbox://styles/STYLE_ID`. ([#2632](https://github.com/mapbox/mapbox-gl-native/pull/2632))
 - Default styles such as Streets are no longer bundled with the SDK; instead, they are loaded at runtime from the style API on mapbox.com. As always, you can use these default styles with any valid access token, and Streets continues to be `MGLMapView`’s initial style. The `bundledStyleURLs` property on `MGLMapView` has been deprecated in favor of several class methods on `MGLStyle` that provide direct access to the default styles. ([#2746](https://github.com/mapbox/mapbox-gl-native/pull/2746))
 - The SDK now builds with Bitcode enabled. A version of libMapbox.a with Bitcode disabled is also available. ([#2332](https://github.com/mapbox/mapbox-gl-native/issues/2332), [#3003](https://github.com/mapbox/mapbox-gl-native/pull/3003))
+- The style URL can be set to a local resource: `asset://local-color.json` and `local-color.json` both resolve to a file named `local-color.json` in the application’s root folder. ([#3087](https://github.com/mapbox/mapbox-gl-native/pull/3087))
 - The double-tap-drag gesture for zooming in and out is now consistent with the Google Maps SDK. ([#2153](https://github.com/mapbox/mapbox-gl-native/pull/2153))
 - A new `MGLAnnotationImage.enabled` property allows you to disable touch events on individual annotations. ([#2501](https://github.com/mapbox/mapbox-gl-native/pull/2501))
 - Fixed a rendering issue that caused one-way arrows along tile boundaries to point due east instead of in the direction of travel. ([#2530](https://github.com/mapbox/mapbox-gl-native/pull/2530))

platform/darwin/asset_root.mm

@@ -2,24 +2,13 @@
 
 #include <mbgl/platform/platform.hpp>
 
-@interface MGLApplicationRootBundleCanary : NSObject
-@end
-
-@implementation MGLApplicationRootBundleCanary
-@end
-
 namespace mbgl {
 namespace platform {
 
 // Returns the path to the root folder of the application.
 const std::string &assetRoot() {
     static const std::string root = []() -> std::string {
-        NSString *path = [[NSBundle bundleForClass:[MGLApplicationRootBundleCanary class]] pathForResource:@"Mapbox" ofType:@"bundle"];
-        if (!path) {
-            path = [[[NSBundle mainBundle] resourceURL] path];
-        }
-        return {[path cStringUsingEncoding : NSUTF8StringEncoding],
-                [path lengthOfBytesUsingEncoding:NSUTF8StringEncoding]};
+        return [[[[NSBundle mainBundle] resourceURL] path] UTF8String];
     }();
     return root;
 }

platform/ios/MGLMapView.mm

@@ -192,8 +192,8 @@ std::chrono::steady_clock::duration durationInSeconds(float duration)
 
     if ( ! [styleURL scheme])
     {
-        // Assume a relative path into the developer’s bundle.
-        styleURL = [[NSBundle mainBundle] URLForResource:styleURL.path withExtension:nil];
+        // Assume a relative path into the application bundle.
+        styleURL = [NSURL URLWithString:[@"asset://" stringByAppendingString:[styleURL absoluteString]]];
     }
 
     _mbglMap->setStyleURL([[styleURL absoluteString] UTF8String]);