Specialize codegen for heatmap-color property

Because `heatmap-color` must be an expression depending only on the `["heatmap-density"]` (`$heatmapDensity`) variable, it's represented in core using a specialized `HeatmapColorPropertyValue` class rather than `PropertyValue<T>` or `DataDrivenPropertyValue<T>`. This change updates the darwin codegen to reflect that.

8 files changed, 86 insertions, 4 deletions

diff --git a/include/mbgl/style/heatmap_color_property_value.hpp b/include/mbgl/style/heatmap_color_property_value.hpp
index a530fc5332..130639c6e2 100644
--- a/include/mbgl/style/heatmap_color_property_value.hpp
+++ b/include/mbgl/style/heatmap_color_property_value.hpp
@@ -40,6 +40,8 @@ public:
 
     bool isDataDriven()     const { return false; }
     bool hasDataDrivenPropertyDifference(const HeatmapColorPropertyValue&) const { return false; }
+    
+    const expression::Expression& getExpression() const { return *value; }
 };
 
 
diff --git a/platform/darwin/scripts/generate-style-code.js b/platform/darwin/scripts/generate-style-code.js
index 59654eca34..ed7204d244 100755
--- a/platform/darwin/scripts/generate-style-code.js
+++ b/platform/darwin/scripts/generate-style-code.js
@@ -311,7 +311,8 @@ global.propertyDoc = function (propertyName, property, layerType, kind) {
         if (property["property-function"]) {
             doc += '* Interpolation and step functions applied to the `$zoomLevel` variable and/or feature attributes\n';
         } else if (property.function === "interpolated") {
-            doc += '* Interpolation and step functions applied to the `$zoomLevel` variable\n\n' +
+            const variable = property.name === 'heatmap-color' ? '$heatmapDensity' : '$zoomLevel';
+            doc += `* Interpolation and step functions applied to the \`${variable}\` variable\n\n` +
                 'This property does not support applying interpolation or step functions to feature attributes.';
         } else {
             doc += '* Step functions applied to the `$zoomLevel` variable\n\n' +
@@ -632,7 +633,6 @@ const layers = _(spec.layer.type.values).map((value, layerType) => {
     }, []);
 
     const paintProperties = Object.keys(spec[`paint_${layerType}`]).reduce((memo, name) => {
-        if (name === 'heatmap-color') return memo;
         spec[`paint_${layerType}`][name].name = name;
         memo.push(spec[`paint_${layerType}`][name]);
         return memo;
diff --git a/platform/darwin/src/MGLHeatmapStyleLayer.h b/platform/darwin/src/MGLHeatmapStyleLayer.h
index 1cecc30441..ebb7461455 100644
--- a/platform/darwin/src/MGLHeatmapStyleLayer.h
+++ b/platform/darwin/src/MGLHeatmapStyleLayer.h
@@ -65,6 +65,27 @@ MGL_EXPORT
 #pragma mark - Accessing the Paint Attributes
 
 /**
+ Defines the color of each point based on its density value in a heatmap. 
+ Should be an expression that uses `["heatmapDensity"]` as input.
+ 
+ The default value of this property is an expression that evaluates to a rainbow
+ color scale from blue to red. Set this property to `nil` to reset it to the
+ default value.
+ 
+ You can set this property to an expression containing any of the following:
+ 
+ * Constant `UIColor` values
+ * Predefined functions, including mathematical and string operators
+ * Conditional expressions
+ * Variable assignments and references to assigned variables
+ * Interpolation and step functions applied to the `$heatmapDensity` variable
+ 
+ This property does not support applying interpolation or step functions to
+ feature attributes.
+ */
+@property (nonatomic, null_resettable) NSExpression *heatmapColor;
+
+/**
  Similar to `heatmapWeight` but controls the intensity of the heatmap globally.
  Primarily used for adjusting the heatmap based on zoom level.
  
diff --git a/platform/darwin/src/MGLHeatmapStyleLayer.mm b/platform/darwin/src/MGLHeatmapStyleLayer.mm
index b210114d90..a394dbda3b 100644
--- a/platform/darwin/src/MGLHeatmapStyleLayer.mm
+++ b/platform/darwin/src/MGLHeatmapStyleLayer.mm
@@ -68,6 +68,23 @@
 
 #pragma mark - Accessing the Paint Attributes
 
+- (void)setHeatmapColor:(NSExpression *)heatmapColor {
+    MGLAssertStyleLayerIsValid();
+
+    auto mbglValue = MGLStyleValueTransformer<mbgl::Color, MGLColor *>().toPropertyValue<mbgl::style::HeatmapColorPropertyValue>(heatmapColor);
+    self.rawLayer->setHeatmapColor(mbglValue);
+}
+
+- (NSExpression *)heatmapColor {
+    MGLAssertStyleLayerIsValid();
+
+    auto propertyValue = self.rawLayer->getHeatmapColor();
+    if (propertyValue.isUndefined()) {
+        propertyValue = self.rawLayer->getDefaultHeatmapColor();
+    }
+    return MGLStyleValueTransformer<mbgl::Color, MGLColor *>().toExpression(propertyValue);
+}
+
 - (void)setHeatmapIntensity:(NSExpression *)heatmapIntensity {
     MGLAssertStyleLayerIsValid();
 
diff --git a/platform/darwin/src/MGLStyleLayer.mm.ejs b/platform/darwin/src/MGLStyleLayer.mm.ejs
index 41b029791f..ac7676a1cc 100644
--- a/platform/darwin/src/MGLStyleLayer.mm.ejs
+++ b/platform/darwin/src/MGLStyleLayer.mm.ejs
@@ -157,7 +157,9 @@ namespace mbgl {
 - (void)set<%- camelize(property.name) %>:(NSExpression *)<%- objCName(property) %> {
     MGLAssertStyleLayerIsValid();
 
-<% if (property["property-function"]) { -%>
+<% if (property.name === 'heatmap-color') { -%>
+    auto mbglValue = MGLStyleValueTransformer<mbgl::Color, MGLColor *>().toPropertyValue<mbgl::style::HeatmapColorPropertyValue>(heatmapColor);
+<% } else if (property["property-function"]) { -%>
     auto mbglValue = MGLStyleValueTransformer<<%- valueTransformerArguments(property).join(', ') %>>().toPropertyValue<mbgl::style::DataDrivenPropertyValue<<%- valueTransformerArguments(property)[0] %>>>(<%- objCName(property) %>);
 <% } else { -%>
     auto mbglValue = MGLStyleValueTransformer<<%- valueTransformerArguments(property).join(', ') %>>().toPropertyValue<mbgl::style::PropertyValue<<%- valueTransformerArguments(property)[0] %>>>(<%- objCName(property) %>);
diff --git a/platform/darwin/src/MGLStyleValue_Private.h b/platform/darwin/src/MGLStyleValue_Private.h
index ba4b413a3c..5124c29a90 100644
--- a/platform/darwin/src/MGLStyleValue_Private.h
+++ b/platform/darwin/src/MGLStyleValue_Private.h
@@ -10,6 +10,7 @@
 #import "MGLConversion.h"
 #include <mbgl/style/conversion/property_value.hpp>
 #include <mbgl/style/conversion/data_driven_property_value.hpp>
+#include <mbgl/style/conversion/heatmap_color_property_value.hpp>
 #include <mbgl/style/conversion/position.hpp>
 #import <mbgl/style/types.hpp>
 
@@ -52,11 +53,20 @@ public:
         return mbglValue.evaluate(evaluator);
     }
     
+    // Convert an mbgl heatmap color property value into an mgl style value
+    NSExpression *toExpression(const mbgl::style::HeatmapColorPropertyValue &mbglValue) {
+        if (mbglValue.isUndefined()) {
+            return nil;
+        }
+        return [NSExpression mgl_expressionWithJSONObject:MGLJSONObjectFromMBGLExpression(mbglValue.getExpression())];
+    }
+
     /**
      Converts an NSExpression to an mbgl property value.
      */
     template <typename MBGLValue>
-    MBGLValue toPropertyValue(NSExpression *expression) {
+    typename std::enable_if_t<!std::is_same<MBGLValue, mbgl::style::HeatmapColorPropertyValue>::value,
+    MBGLValue> toPropertyValue(NSExpression *expression) {
         if (!expression) {
             return {};
         }
@@ -85,6 +95,30 @@ public:
         
         return *value;
     }
+    
+    /**
+     Converts an NSExpression to an mbgl property value.
+     */
+    template <typename MBGLValue>
+    typename std::enable_if_t<std::is_same<MBGLValue, mbgl::style::HeatmapColorPropertyValue>::value,
+    MBGLValue> toPropertyValue(NSExpression *expression) {
+        if (!expression) {
+            return {};
+        }
+        
+        NSArray *jsonExpression = expression.mgl_jsonExpressionObject;
+        
+        mbgl::style::conversion::Error valueError;
+        auto value = mbgl::style::conversion::convert<mbgl::style::HeatmapColorPropertyValue>(
+            mbgl::style::conversion::makeConvertible(jsonExpression), valueError);
+        if (!value) {
+            [NSException raise:NSInvalidArgumentException
+                        format:@"Invalid property value: %@", @(valueError.message.c_str())];
+            return {};
+        }
+        
+        return *value;
+    }
 
 private: // Private utilities for converting from mgl to mbgl values
     
diff --git a/platform/darwin/test/MGLStyleLayerTests.mm.ejs b/platform/darwin/test/MGLStyleLayerTests.mm.ejs
index e26c63e662..e17501ed18 100644
--- a/platform/darwin/test/MGLStyleLayerTests.mm.ejs
+++ b/platform/darwin/test/MGLStyleLayerTests.mm.ejs
@@ -59,6 +59,7 @@
     MGLTransition transitionTest = MGLTransitionMake(5, 4);
 
 <% for (const property of properties) { -%>
+<%   if (property.name === 'heatmap-color') continue; -%>
 
     // <%- originalPropertyName(property) %>
     {
@@ -151,6 +152,7 @@
 
 - (void)testPropertyNames {
 <% for (const property of properties) { -%>
+<%   if (property.name === 'heatmap-color') continue; -%>
     [self testPropertyName:@"<%- property.getter || property.name %>" isBoolean:<%- property.type === 'boolean' ? 'YES' : 'NO' %>];
 <% } -%>
 }
diff --git a/platform/macos/macos.xcodeproj/project.pbxproj b/platform/macos/macos.xcodeproj/project.pbxproj
index 30458d92fe..c3e8242943 100644
--- a/platform/macos/macos.xcodeproj/project.pbxproj
+++ b/platform/macos/macos.xcodeproj/project.pbxproj
@@ -16,6 +16,7 @@
 		07D9474D1F67441B00E37934 /* MGLAbstractShapeSource_Private.h in Headers */ = {isa = PBXBuildFile; fileRef = 07D947471F6741F500E37934 /* MGLAbstractShapeSource_Private.h */; };
 		07F8E2F71F674C8800F794BB /* MGLComputedShapeSource.h in Headers */ = {isa = PBXBuildFile; fileRef = 07F8E2F41F674C8000F794BB /* MGLComputedShapeSource.h */; settings = {ATTRIBUTES = (Public, ); }; };
 		07F8E2F81F674C9000F794BB /* MGLComputedShapeSource.mm in Sources */ = {isa = PBXBuildFile; fileRef = 07F8E2F51F674C8000F794BB /* MGLComputedShapeSource.mm */; };
+		170A82BF201BDD1B00943087 /* MGLHeatmapStyleLayerTests.mm in Sources */ = {isa = PBXBuildFile; fileRef = 170A82BE201BDD1B00943087 /* MGLHeatmapStyleLayerTests.mm */; };
 		1753ED401E53CE6100A9FD90 /* MGLConversion.h in Headers */ = {isa = PBXBuildFile; fileRef = 1753ED3F1E53CE5200A9FD90 /* MGLConversion.h */; };
 		1F7454A31ECFB00300021D39 /* MGLLight_Private.h in Headers */ = {isa = PBXBuildFile; fileRef = 1F7454A01ECFB00300021D39 /* MGLLight_Private.h */; };
 		1F7454A41ECFB00300021D39 /* MGLLight.h in Headers */ = {isa = PBXBuildFile; fileRef = 1F7454A11ECFB00300021D39 /* MGLLight.h */; settings = {ATTRIBUTES = (Public, ); }; };
@@ -301,6 +302,7 @@
 		07D947491F6741F500E37934 /* MGLAbstractShapeSource.mm */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.objcpp; path = MGLAbstractShapeSource.mm; sourceTree = "<group>"; };
 		07F8E2F41F674C8000F794BB /* MGLComputedShapeSource.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = MGLComputedShapeSource.h; sourceTree = "<group>"; };
 		07F8E2F51F674C8000F794BB /* MGLComputedShapeSource.mm */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.objcpp; path = MGLComputedShapeSource.mm; sourceTree = "<group>"; };
+		170A82BE201BDD1B00943087 /* MGLHeatmapStyleLayerTests.mm */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.cpp.objcpp; path = MGLHeatmapStyleLayerTests.mm; sourceTree = "<group>"; };
 		1753ED3F1E53CE5200A9FD90 /* MGLConversion.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = MGLConversion.h; sourceTree = "<group>"; };
 		1F7454A01ECFB00300021D39 /* MGLLight_Private.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = MGLLight_Private.h; sourceTree = "<group>"; };
 		1F7454A11ECFB00300021D39 /* MGLLight.h */ = {isa = PBXFileReference; fileEncoding = 4; lastKnownFileType = sourcecode.c.h; path = MGLLight.h; sourceTree = "<group>"; };
@@ -884,6 +886,7 @@
 		DA8F257C1D51C5F40010E6B5 /* Layers */ = {
 			isa = PBXGroup;
 			children = (
+				170A82BE201BDD1B00943087 /* MGLHeatmapStyleLayerTests.mm */,
 				40E1601A1DF216E6005EA6D9 /* MGLStyleLayerTests.h */,
 				40E1601B1DF216E6005EA6D9 /* MGLStyleLayerTests.m */,
 				DA2207BA1DC076930002F84D /* test-Bridging-Header.h */,
@@ -1577,6 +1580,7 @@
 				DAE6C3D21CC34C9900DB3429 /* MGLGeometryTests.mm in Sources */,
 				DA87A9A41DCACC5000810D09 /* MGLSymbolStyleLayerTests.mm in Sources */,
 				40E1601D1DF217D6005EA6D9 /* MGLStyleLayerTests.m in Sources */,
+				170A82BF201BDD1B00943087 /* MGLHeatmapStyleLayerTests.mm in Sources */,
 				1F95931B1E6DE2B600D5B294 /* MGLNSDateAdditionsTests.mm in Sources */,
 				DAF25721201902C100367EF5 /* MGLHillshadeStyleLayerTests.mm in Sources */,
 				DA87A9A61DCACC5000810D09 /* MGLCircleStyleLayerTests.mm in Sources */,