[core, darwin] Object identity for MGLSource*, MGLStyleLayer*

All `MGLSource` pointers referencing the same logical source will now be object identical; similarly for `MGLStyleLayer`.

12 files changed, 66 insertions, 20 deletions

diff --git a/CMakeLists.txt b/CMakeLists.txt
index a6ed681bde..9e7ee314e7 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -40,6 +40,7 @@ set_source_files_properties(src/mbgl/util/version.cpp PROPERTIES COMPILE_DEFINIT
 
 mason_use(geometry VERSION 0.9.0 HEADER_ONLY)
 mason_use(variant VERSION 1.1.4 HEADER_ONLY)
+mason_use(any VERSION 8fef1e9 HEADER_ONLY)
 mason_use(unique_resource VERSION cba309e HEADER_ONLY)
 mason_use(rapidjson VERSION 1.1.0 HEADER_ONLY)
 mason_use(boost VERSION 1.62.0 HEADER_ONLY)
diff --git a/cmake/core.cmake b/cmake/core.cmake
index 616e43028c..531edc092d 100644
--- a/cmake/core.cmake
+++ b/cmake/core.cmake
@@ -14,6 +14,7 @@ target_include_directories(mbgl-core
 
 target_add_mason_package(mbgl-core PUBLIC geometry)
 target_add_mason_package(mbgl-core PUBLIC variant)
+target_add_mason_package(mbgl-core PUBLIC any)
 target_add_mason_package(mbgl-core PRIVATE unique_resource)
 target_add_mason_package(mbgl-core PRIVATE rapidjson)
 target_add_mason_package(mbgl-core PRIVATE boost)
diff --git a/cmake/test.cmake b/cmake/test.cmake
index 5e77de2448..3c63f7bcf8 100644
--- a/cmake/test.cmake
+++ b/cmake/test.cmake
@@ -27,6 +27,7 @@ target_link_libraries(mbgl-test
 
 target_add_mason_package(mbgl-test PRIVATE geometry)
 target_add_mason_package(mbgl-test PRIVATE variant)
+target_add_mason_package(mbgl-test PRIVATE any)
 target_add_mason_package(mbgl-test PRIVATE unique_resource)
 target_add_mason_package(mbgl-test PRIVATE rapidjson)
 target_add_mason_package(mbgl-test PRIVATE gtest)
diff --git a/include/mbgl/style/layer.hpp b/include/mbgl/style/layer.hpp
index 670faa8254..fa88b30dbc 100644
--- a/include/mbgl/style/layer.hpp
+++ b/include/mbgl/style/layer.hpp
@@ -1,6 +1,7 @@
 #pragma once
 
 #include <mbgl/util/noncopyable.hpp>
+#include <mbgl/util/any.hpp>
 #include <mbgl/style/types.hpp>
 
 #include <memory>
@@ -118,6 +119,11 @@ public:
     // Private implementation
     const std::unique_ptr<Impl> baseImpl;
 
+    // For use in SDK bindings, which store a reference to a platform-native peer
+    // object here, so that separately-obtained references to this object share
+    // identical platform-native peers.
+    any peer;
+
     friend std::string layoutKey(const Layer&);
 };
 
diff --git a/include/mbgl/style/source.hpp b/include/mbgl/style/source.hpp
index 0e6e32b112..f2dfb6a896 100644
--- a/include/mbgl/style/source.hpp
+++ b/include/mbgl/style/source.hpp
@@ -4,6 +4,7 @@
 #include <mbgl/util/noncopyable.hpp>
 #include <mbgl/util/optional.hpp>
 #include <mbgl/util/range.hpp>
+#include <mbgl/util/any.hpp>
 #include <mbgl/style/types.hpp>
 #include <mbgl/style/query.hpp>
 
@@ -64,6 +65,11 @@ public:
     class Impl;
     const std::unique_ptr<Impl> baseImpl;
 
+    // For use in SDK bindings, which store a reference to a platform-native peer
+    // object here, so that separately-obtained references to this object share
+    // identical platform-native peers.
+    any peer;
+
 protected:
     const SourceType type;
     Source(SourceType, std::unique_ptr<Impl>);
diff --git a/include/mbgl/util/any.hpp b/include/mbgl/util/any.hpp
new file mode 100644
index 0000000000..eea64b188a
--- /dev/null
+++ b/include/mbgl/util/any.hpp
@@ -0,0 +1,10 @@
+#pragma once
+
+#include <linb/any.hpp>
+
+namespace mbgl {
+
+using linb::any;
+using linb::any_cast;
+
+} // namespace mbgl
diff --git a/platform/darwin/src/MGLSource.mm b/platform/darwin/src/MGLSource.mm
index 1940db688c..59c2ae13e6 100644
--- a/platform/darwin/src/MGLSource.mm
+++ b/platform/darwin/src/MGLSource.mm
@@ -29,6 +29,7 @@
     NSString *identifier = @(rawSource->getID().c_str());
     if (self = [self initWithIdentifier:identifier]) {
         _rawSource = rawSource;
+        _rawSource->peer = SourceWrapper { self };
     }
     return self;
 }
diff --git a/platform/darwin/src/MGLSource_Private.h b/platform/darwin/src/MGLSource_Private.h
index 2fc170b86b..6f86e4800b 100644
--- a/platform/darwin/src/MGLSource_Private.h
+++ b/platform/darwin/src/MGLSource_Private.h
@@ -10,6 +10,14 @@ namespace mbgl {
     }
 }
 
+// A struct to be stored in the `peer` member of mbgl::style::Source, in order to implement
+// object identity. We don't store a MGLSource pointer directly because that doesn't
+// interoperate with ARC. The inner pointer is weak in order to avoid a reference cycle for
+// "pending" MGLSources, which have a strong owning pointer to the mbgl::style::Source.
+struct SourceWrapper {
+    __weak MGLSource *source;
+};
+
 @class MGLMapView;
 
 @interface MGLSource (Private)
diff --git a/platform/darwin/src/MGLStyle.mm b/platform/darwin/src/MGLStyle.mm
index 83ff73e8f9..b01d9aa513 100644
--- a/platform/darwin/src/MGLStyle.mm
+++ b/platform/darwin/src/MGLStyle.mm
@@ -166,17 +166,21 @@ static NSURL *MGLStyleURL_emerald;
     return rawSource ? [self sourceFromMBGLSource:rawSource] : nil;
 }
 
-- (MGLSource *)sourceFromMBGLSource:(mbgl::style::Source *)source {
+- (MGLSource *)sourceFromMBGLSource:(mbgl::style::Source *)rawSource {
+    if (MGLSource *source = rawSource->peer.empty() ? nil : mbgl::any_cast<SourceWrapper>(rawSource->peer).source) {
+        return source;
+    }
+
     // TODO: Fill in options specific to the respective source classes
     // https://github.com/mapbox/mapbox-gl-native/issues/6584
-    if (auto vectorSource = source->as<mbgl::style::VectorSource>()) {
+    if (auto vectorSource = rawSource->as<mbgl::style::VectorSource>()) {
         return [[MGLVectorSource alloc] initWithRawSource:vectorSource];
-    } else if (auto geoJSONSource = source->as<mbgl::style::GeoJSONSource>()) {
+    } else if (auto geoJSONSource = rawSource->as<mbgl::style::GeoJSONSource>()) {
         return [[MGLShapeSource alloc] initWithRawSource:geoJSONSource];
-    } else if (auto rasterSource = source->as<mbgl::style::RasterSource>()) {
+    } else if (auto rasterSource = rawSource->as<mbgl::style::RasterSource>()) {
         return [[MGLRasterSource alloc] initWithRawSource:rasterSource];
     } else {
-        return [[MGLSource alloc] initWithRawSource:source];
+        return [[MGLSource alloc] initWithRawSource:rawSource];
     }
 }
 
@@ -319,35 +323,32 @@ static NSURL *MGLStyleURL_emerald;
     [styleLayer removeFromMapView:self.mapView];
 }
 
-- (MGLStyleLayer *)layerFromMBGLLayer:(mbgl::style::Layer *)mbglLayer
+- (MGLStyleLayer *)layerFromMBGLLayer:(mbgl::style::Layer *)rawLayer
 {
-    NSParameterAssert(mbglLayer);
+    NSParameterAssert(rawLayer);
 
-    NSString *identifier = @(mbglLayer->getID().c_str());
+    if (MGLStyleLayer *layer = rawLayer->peer.empty() ? nil : mbgl::any_cast<LayerWrapper>(rawLayer->peer).layer) {
+        return layer;
+    }
 
-    if (auto fillLayer = mbglLayer->as<mbgl::style::FillLayer>()) {
+    if (auto fillLayer = rawLayer->as<mbgl::style::FillLayer>()) {
         MGLSource *source = [self sourceWithIdentifier:@(fillLayer->getSourceID().c_str())];
         return [[MGLFillStyleLayer alloc] initWithRawLayer:fillLayer source:source];
-    } else if (auto lineLayer = mbglLayer->as<mbgl::style::LineLayer>()) {
+    } else if (auto lineLayer = rawLayer->as<mbgl::style::LineLayer>()) {
         MGLSource *source = [self sourceWithIdentifier:@(lineLayer->getSourceID().c_str())];
         return [[MGLLineStyleLayer alloc] initWithRawLayer:lineLayer source:source];
-    } else if (auto symbolLayer = mbglLayer->as<mbgl::style::SymbolLayer>()) {
+    } else if (auto symbolLayer = rawLayer->as<mbgl::style::SymbolLayer>()) {
         MGLSource *source = [self sourceWithIdentifier:@(symbolLayer->getSourceID().c_str())];
         return [[MGLSymbolStyleLayer alloc] initWithRawLayer:symbolLayer source:source];
-    } else if (auto rasterLayer = mbglLayer->as<mbgl::style::RasterLayer>()) {
+    } else if (auto rasterLayer = rawLayer->as<mbgl::style::RasterLayer>()) {
         MGLSource *source = [self sourceWithIdentifier:@(rasterLayer->getSourceID().c_str())];
         return [[MGLRasterStyleLayer alloc] initWithRawLayer:rasterLayer source:source];
-    } else if (auto circleLayer = mbglLayer->as<mbgl::style::CircleLayer>()) {
+    } else if (auto circleLayer = rawLayer->as<mbgl::style::CircleLayer>()) {
         MGLSource *source = [self sourceWithIdentifier:@(circleLayer->getSourceID().c_str())];
         return [[MGLCircleStyleLayer alloc] initWithRawLayer:circleLayer source:source];
-    } else if (auto backgroundLayer = mbglLayer->as<mbgl::style::BackgroundLayer>()) {
+    } else if (auto backgroundLayer = rawLayer->as<mbgl::style::BackgroundLayer>()) {
         return [[MGLBackgroundStyleLayer alloc] initWithRawLayer:backgroundLayer];
-    } else if (auto customLayer = mbglLayer->as<mbgl::style::CustomLayer>()) {
-        MGLStyleLayer *styleLayer = self.openGLLayers[identifier];
-        if (styleLayer) {
-            NSAssert(styleLayer.rawLayer == customLayer, @"%@ wraps a CustomLayer that differs from the one associated with the underlying style.", styleLayer);
-            return styleLayer;
-        }
+    } else if (auto customLayer = rawLayer->as<mbgl::style::CustomLayer>()) {
         return [[MGLOpenGLStyleLayer alloc] initWithRawLayer:customLayer];
     } else {
         NSAssert(NO, @"Unrecognized layer type");
diff --git a/platform/darwin/src/MGLStyleLayer.mm b/platform/darwin/src/MGLStyleLayer.mm
index c72541526f..4bfaea934b 100644
--- a/platform/darwin/src/MGLStyleLayer.mm
+++ b/platform/darwin/src/MGLStyleLayer.mm
@@ -18,6 +18,7 @@
     if (self = [super init]) {
         _identifier = @(rawLayer->getID().c_str());
         _rawLayer = rawLayer;
+        _rawLayer->peer = LayerWrapper { self };
     }
     return self;
 }
diff --git a/platform/darwin/src/MGLStyleLayer_Private.h b/platform/darwin/src/MGLStyleLayer_Private.h
index d024a0bb13..ed8ec31755 100644
--- a/platform/darwin/src/MGLStyleLayer_Private.h
+++ b/platform/darwin/src/MGLStyleLayer_Private.h
@@ -7,6 +7,14 @@
 
 NS_ASSUME_NONNULL_BEGIN
 
+// A struct to be stored in the `peer` member of mbgl::style::Layer, in order to implement
+// object identity. We don't store a MGLStyleLayer pointer directly because that doesn't
+// interoperate with ARC. The inner pointer is weak in order to avoid a reference cycle for
+// "pending" MGLStyleLayers, which have a strong owning pointer to the mbgl::style::Layer.
+struct LayerWrapper {
+    __weak MGLStyleLayer *layer;
+};
+
 /**
  Assert that the style layer is valid.
 
diff --git a/platform/darwin/test/MGLStyleTests.mm b/platform/darwin/test/MGLStyleTests.mm
index 36772e556d..f9598a143d 100644
--- a/platform/darwin/test/MGLStyleTests.mm
+++ b/platform/darwin/test/MGLStyleTests.mm
@@ -148,6 +148,7 @@
     MGLShapeSource *shapeSource = [[MGLShapeSource alloc] initWithIdentifier:@"shapeSource" shape:nil options:nil];
     [self.style addSource:shapeSource];
     XCTAssertEqual(self.style.sources.count, initialSources.count + 1);
+    XCTAssertEqual(shapeSource, [self.style sourceWithIdentifier:@"shapeSource"]);
     [self.style removeSource:shapeSource];
     XCTAssertEqual(self.style.sources.count, initialSources.count);
 }
@@ -238,6 +239,7 @@
     MGLFillStyleLayer *fillLayer = [[MGLFillStyleLayer alloc] initWithIdentifier:@"fillLayer" source:shapeSource];
     [self.style addLayer:fillLayer];
     XCTAssertEqual(self.style.layers.count, initialLayers.count + 1);
+    XCTAssertEqual(fillLayer, [self.style layerWithIdentifier:@"fillLayer"]);
     [self.style removeLayer:fillLayer];
     XCTAssertEqual(self.style.layers.count, initialLayers.count);
 }