[ios, macos] Raise NSException if layer or source added more than once

When MGLSource and MGLLayer instances are added to the style, they lose
ownership of their std::unique_ptr<T> after it is moved to the mbgl
level. Subsequent attempts to add such instances result in a C++
exception.

This adds logic in the Darwin platform to raise a NSException if the
source and layer addToMapView methods are called more than once and the
pointer is invalid. In addition, the documentation in MGLStyle for
addSource: and addLayer: has been update to warn developers to avoid
adding the same instance twice and, for that matter, instances with the
same identifier.

12 files changed, 135 insertions, 1 deletions

diff --git a/platform/darwin/src/MGLBackgroundStyleLayer.mm b/platform/darwin/src/MGLBackgroundStyleLayer.mm
index c8f8b39b3e..253414852a 100644
--- a/platform/darwin/src/MGLBackgroundStyleLayer.mm
+++ b/platform/darwin/src/MGLBackgroundStyleLayer.mm
@@ -35,6 +35,12 @@
 
 - (void)addToMapView:(MGLMapView *)mapView
 {
+    if (_pendingLayer == nullptr) {
+        [NSException raise:@"MGLRedundantLayerException"
+            format:@"This instance %@ was already added to %@. Adding the same layer instance " \
+                    "to the style more than once is invalid.", self, mapView.style];
+    }
+
     [self addToMapView:mapView belowLayer:nil];
 }
 
diff --git a/platform/darwin/src/MGLCircleStyleLayer.mm b/platform/darwin/src/MGLCircleStyleLayer.mm
index 7768ff66c9..91f91a7bcd 100644
--- a/platform/darwin/src/MGLCircleStyleLayer.mm
+++ b/platform/darwin/src/MGLCircleStyleLayer.mm
@@ -75,6 +75,12 @@ namespace mbgl {
 
 - (void)addToMapView:(MGLMapView *)mapView
 {
+    if (_pendingLayer == nullptr) {
+        [NSException raise:@"MGLRedundantLayerException"
+            format:@"This instance %@ was already added to %@. Adding the same layer instance " \
+                    "to the style more than once is invalid.", self, mapView.style];
+    }
+
     [self addToMapView:mapView belowLayer:nil];
 }
 
diff --git a/platform/darwin/src/MGLFillStyleLayer.mm b/platform/darwin/src/MGLFillStyleLayer.mm
index d1a96f7230..87a5144c6b 100644
--- a/platform/darwin/src/MGLFillStyleLayer.mm
+++ b/platform/darwin/src/MGLFillStyleLayer.mm
@@ -70,6 +70,12 @@ namespace mbgl {
 
 - (void)addToMapView:(MGLMapView *)mapView
 {
+    if (_pendingLayer == nullptr) {
+        [NSException raise:@"MGLRedundantLayerException"
+            format:@"This instance %@ was already added to %@. Adding the same layer instance " \
+                    "to the style more than once is invalid.", self, mapView.style];
+    }
+
     [self addToMapView:mapView belowLayer:nil];
 }
 
diff --git a/platform/darwin/src/MGLGeoJSONSource.mm b/platform/darwin/src/MGLGeoJSONSource.mm
index f7cd6be7df..8b37ba47cd 100644
--- a/platform/darwin/src/MGLGeoJSONSource.mm
+++ b/platform/darwin/src/MGLGeoJSONSource.mm
@@ -61,6 +61,12 @@ const MGLGeoJSONSourceOption MGLGeoJSONSourceOptionSimplificationTolerance = @"M
 
 - (void)addToMapView:(MGLMapView *)mapView
 {
+    if (_pendingSource == nullptr) {
+        [NSException raise:@"MGLRedundantSourceException"
+                    format:@"This instance %@ was already added to %@. Adding the same source instance " \
+                            "to the style more than once is invalid.", self, mapView.style];
+    }
+
     mapView.mbglMap->addSource(std::move(_pendingSource));
 }
 
diff --git a/platform/darwin/src/MGLLineStyleLayer.mm b/platform/darwin/src/MGLLineStyleLayer.mm
index a7ed2fc100..b155ec65d6 100644
--- a/platform/darwin/src/MGLLineStyleLayer.mm
+++ b/platform/darwin/src/MGLLineStyleLayer.mm
@@ -82,6 +82,12 @@ namespace mbgl {
 
 - (void)addToMapView:(MGLMapView *)mapView
 {
+    if (_pendingLayer == nullptr) {
+        [NSException raise:@"MGLRedundantLayerException"
+            format:@"This instance %@ was already added to %@. Adding the same layer instance " \
+                    "to the style more than once is invalid.", self, mapView.style];
+    }
+
     [self addToMapView:mapView belowLayer:nil];
 }
 
diff --git a/platform/darwin/src/MGLRasterSource.mm b/platform/darwin/src/MGLRasterSource.mm
index 53caae5af9..62472050e3 100644
--- a/platform/darwin/src/MGLRasterSource.mm
+++ b/platform/darwin/src/MGLRasterSource.mm
@@ -62,6 +62,12 @@
 
 - (void)addToMapView:(MGLMapView *)mapView
 {
+    if (_pendingSource == nullptr) {
+        [NSException raise:@"MGLRedundantSourceException"
+                    format:@"This instance %@ was already added to %@. Adding the same source instance " \
+                            "to the style more than once is invalid.", self, mapView.style];
+    }
+
     mapView.mbglMap->addSource(std::move(_pendingSource));
 }
 
diff --git a/platform/darwin/src/MGLRasterStyleLayer.mm b/platform/darwin/src/MGLRasterStyleLayer.mm
index 24dba21c71..3b2c3bd83b 100644
--- a/platform/darwin/src/MGLRasterStyleLayer.mm
+++ b/platform/darwin/src/MGLRasterStyleLayer.mm
@@ -34,6 +34,12 @@
 
 - (void)addToMapView:(MGLMapView *)mapView
 {
+    if (_pendingLayer == nullptr) {
+        [NSException raise:@"MGLRedundantLayerException"
+            format:@"This instance %@ was already added to %@. Adding the same layer instance " \
+                    "to the style more than once is invalid.", self, mapView.style];
+    }
+
     [self addToMapView:mapView belowLayer:nil];
 }
 
diff --git a/platform/darwin/src/MGLStyle.h b/platform/darwin/src/MGLStyle.h
index 10fad0196e..31808290f9 100644
--- a/platform/darwin/src/MGLStyle.h
+++ b/platform/darwin/src/MGLStyle.h
@@ -200,6 +200,9 @@ static const NSInteger MGLStyleDefaultVersion = 9;
 /**
  Adds a new source to the current style.
  
+ @note Adding the same source instance more than once or reusing source 
+    identifers in the sources you add will trigger exceptions.
+ 
  @param source The source to add to the current style.
  */
 - (void)addSource:(MGLSource *)source;
@@ -247,6 +250,9 @@ static const NSInteger MGLStyleDefaultVersion = 9;
 /**
  Adds a new layer on top of existing layers.
 
+ @note Adding the same layer instance more than once or reusing layer
+    identifers in the layers you add will trigger exceptions.
+
  @param layer The layer object to add to the map view. This object must be an
     instance of a concrete subclass of `MGLStyleLayer`.
  */
@@ -255,6 +261,9 @@ static const NSInteger MGLStyleDefaultVersion = 9;
 /**
  Inserts a new layer into the style at the given index.
  
+ @note Adding the same layer instance more than once or reusing layer
+    identifers in the layers you add will trigger exceptions.
+ 
  @param layer The layer to insert.
  @param index The index at which to insert the layer. An index of 0 would send
     the layer to the back; an index equal to the number of objects in the
@@ -272,6 +281,9 @@ static const NSInteger MGLStyleDefaultVersion = 9;
     inspectable in Interface Builder, or a manually constructed `NSURL`. This
     approach also avoids layer identifer name changes that will occur in the default
     style’s layers over time.
+ 
+    Adding the same layer instance more than once or reusing layer identifers in 
+    the layers you add will trigger exceptions.
 
  @param layer The layer to insert.
  @param sibling An existing layer in the style.
@@ -288,6 +300,9 @@ static const NSInteger MGLStyleDefaultVersion = 9;
     inspectable in Interface Builder, or a manually constructed `NSURL`. This
     approach also avoids layer identifer name changes that will occur in the default
     style’s layers over time.
+ 
+    Adding the same layer instance more than once or reusing layer identifers in
+    the layers you add will trigger exceptions.
 
  @param layer The layer to insert.
  @param sibling An existing layer in the style.
diff --git a/platform/darwin/src/MGLStyleLayer.mm.ejs b/platform/darwin/src/MGLStyleLayer.mm.ejs
index 85a1af9970..c89912c1ff 100644
--- a/platform/darwin/src/MGLStyleLayer.mm.ejs
+++ b/platform/darwin/src/MGLStyleLayer.mm.ejs
@@ -112,6 +112,12 @@ namespace mbgl {
 
 - (void)addToMapView:(MGLMapView *)mapView
 {
+    if (_pendingLayer == nullptr) {
+        [NSException raise:@"MGLRedundantLayerException"
+            format:@"This instance %@ was already added to %@. Adding the same layer instance " \
+                    "to the style more than once is invalid.", self, mapView.style];
+    }
+
     [self addToMapView:mapView belowLayer:nil];
 }
 
diff --git a/platform/darwin/src/MGLSymbolStyleLayer.mm b/platform/darwin/src/MGLSymbolStyleLayer.mm
index 29fe322181..d1d66f8ffb 100644
--- a/platform/darwin/src/MGLSymbolStyleLayer.mm
+++ b/platform/darwin/src/MGLSymbolStyleLayer.mm
@@ -129,6 +129,12 @@ namespace mbgl {
 
 - (void)addToMapView:(MGLMapView *)mapView
 {
+    if (_pendingLayer == nullptr) {
+        [NSException raise:@"MGLRedundantLayerException"
+            format:@"This instance %@ was already added to %@. Adding the same layer instance " \
+                    "to the style more than once is invalid.", self, mapView.style];
+    }
+
     [self addToMapView:mapView belowLayer:nil];
 }
 
diff --git a/platform/darwin/src/MGLVectorSource.mm b/platform/darwin/src/MGLVectorSource.mm
index ae69456b45..ab68d45ba1 100644
--- a/platform/darwin/src/MGLVectorSource.mm
+++ b/platform/darwin/src/MGLVectorSource.mm
@@ -59,6 +59,12 @@
 
 - (void)addToMapView:(MGLMapView *)mapView
 {
+    if (_pendingSource == nullptr) {
+        [NSException raise:@"MGLRedundantSourceException"
+                    format:@"This instance %@ was already added to %@. Adding the same source instance " \
+                            "to the style more than once is invalid.", self, mapView.style];
+    }
+
     mapView.mbglMap->addSource(std::move(_pendingSource));
 }
 
diff --git a/platform/darwin/test/MGLStyleTests.mm b/platform/darwin/test/MGLStyleTests.mm
index 07e012edc6..6a6a4a827f 100644
--- a/platform/darwin/test/MGLStyleTests.mm
+++ b/platform/darwin/test/MGLStyleTests.mm
@@ -1,4 +1,16 @@
-#import "MGLStyle.h"
+#import "MGLMapView.h"
+#import "MGLStyle_Private.h"
+
+#import "MGLGeoJSONSource.h"
+#import "MGLRasterSource.h"
+#import "MGLVectorSource.h"
+
+#import "MGLBackgroundStyleLayer.h"
+#import "MGLCircleStyleLayer.h"
+#import "MGLFillStyleLayer.h"
+#import "MGLLineStyleLayer.h"
+#import "MGLRasterStyleLayer.h"
+#import "MGLSymbolStyleLayer.h"
 
 #import "NSBundle+MGLAdditions.h"
 
@@ -92,6 +104,53 @@
     }];
 }
 
+- (void)testAddingSourcesTwice {
+    MGLMapView *mapView = [[MGLMapView alloc] initWithFrame:CGRectMake(0, 0, 100, 100)];
+    MGLStyle *style = [[MGLStyle alloc] initWithMapView:mapView];
+
+    MGLGeoJSONSource *geoJSONSource = [[MGLGeoJSONSource alloc] initWithIdentifier:@"geoJSONSource" features:@[] options:nil];
+    [style addSource:geoJSONSource];
+    XCTAssertThrowsSpecificNamed([style addSource:geoJSONSource], NSException, @"MGLRedundantSourceException");
+
+    MGLRasterSource *rasterSource = [[MGLRasterSource alloc] initWithIdentifier:@"rasterSource" URL:[NSURL new] tileSize:42];
+    [style addSource:rasterSource];
+    XCTAssertThrowsSpecificNamed([style addSource:rasterSource], NSException, @"MGLRedundantSourceException");
+
+    MGLVectorSource *vectorSource = [[MGLVectorSource alloc] initWithIdentifier:@"vectorSource" URL:[NSURL new]];
+    [style addSource:vectorSource];
+    XCTAssertThrowsSpecificNamed([style addSource:vectorSource], NSException, @"MGLRedundantSourceException");
+}
+
+- (void)testAddingLayersTwice {
+    MGLMapView *mapView = [[MGLMapView alloc] initWithFrame:CGRectMake(0, 0, 100, 100)];
+    MGLStyle *style = [[MGLStyle alloc] initWithMapView:mapView];
+    MGLGeoJSONSource *source = [[MGLGeoJSONSource alloc] initWithIdentifier:@"geoJSONSource" features:@[] options:nil];
+
+    MGLBackgroundStyleLayer *backgroundLayer = [[MGLBackgroundStyleLayer alloc] initWithIdentifier:@"backgroundLayer"];
+    [style addLayer:backgroundLayer];
+    XCTAssertThrowsSpecificNamed([style addLayer:backgroundLayer], NSException, @"MGLRedundantLayerException");
+
+    MGLCircleStyleLayer *circleLayer = [[MGLCircleStyleLayer alloc] initWithIdentifier:@"circleLayer" source:source];
+    [style addLayer:circleLayer];
+    XCTAssertThrowsSpecificNamed([style addLayer:circleLayer], NSException, @"MGLRedundantLayerException");
+
+    MGLFillStyleLayer *fillLayer = [[MGLFillStyleLayer alloc] initWithIdentifier:@"fillLayer" source:source];
+    [style addLayer:fillLayer];
+    XCTAssertThrowsSpecificNamed([style addLayer:fillLayer], NSException, @"MGLRedundantLayerException");
+
+    MGLLineStyleLayer *lineLayer = [[MGLLineStyleLayer alloc] initWithIdentifier:@"lineLayer" source:source];
+    [style addLayer:lineLayer];
+    XCTAssertThrowsSpecificNamed([style addLayer:lineLayer], NSException, @"MGLRedundantLayerException");
+
+    MGLRasterStyleLayer *rasterLayer = [[MGLRasterStyleLayer alloc] initWithIdentifier:@"rasterLayer" source:source];
+    [style addLayer:rasterLayer];
+    XCTAssertThrowsSpecificNamed([style addLayer:rasterLayer], NSException, @"MGLRedundantLayerException");
+
+    MGLSymbolStyleLayer *symbolLayer = [[MGLSymbolStyleLayer alloc] initWithIdentifier:@"symbolLayer" source:source];
+    [style addLayer:symbolLayer];
+    XCTAssertThrowsSpecificNamed([style addLayer:symbolLayer], NSException, @"MGLRedundantLayerException");
+}
+
 - (NSString *)stringWithContentsOfStyleHeader {
     NSURL *styleHeaderURL = [[[NSBundle mgl_frameworkBundle].bundleURL
                               URLByAppendingPathComponent:@"Headers" isDirectory:YES]