Merge branch 'release-boba' into masterupstream/fabian-merge-v4.0.0

# Conflicts:
#	circle.yml
#	include/mbgl/style/expression/let.hpp
#	platform/android/MapboxGLAndroidSDK/src/main/java/com/mapbox/mapboxsdk/geometry/LatLngBounds.java
#	platform/android/MapboxGLAndroidSDK/src/main/java/com/mapbox/mapboxsdk/maps/MapGestureDetector.java
#	platform/android/MapboxGLAndroidSDK/src/main/java/com/mapbox/mapboxsdk/maps/MapKeyListener.java
#	platform/android/MapboxGLAndroidSDK/src/main/java/com/mapbox/mapboxsdk/maps/MapView.java
#	platform/android/MapboxGLAndroidSDK/src/main/java/com/mapbox/mapboxsdk/maps/MapboxMap.java
#	platform/android/MapboxGLAndroidSDK/src/main/java/com/mapbox/mapboxsdk/maps/Projection.java
#	platform/android/MapboxGLAndroidSDK/src/main/java/com/mapbox/mapboxsdk/maps/Transform.java
#	platform/android/MapboxGLAndroidSDK/src/test/java/com/mapbox/mapboxsdk/geometry/LatLngBoundsTest.java
#	platform/android/MapboxGLAndroidSDKTestApp/src/main/AndroidManifest.xml
#	platform/android/gradle/dependencies.gradle
#	platform/android/src/example_custom_layer.cpp
#	platform/android/src/geojson/point.cpp
#	platform/darwin/src/NSPredicate+MGLAdditions.mm
#	platform/darwin/test/MGLExpressionTests.mm
#	platform/ios/Mapbox-iOS-SDK-nightly-dynamic.podspec
#	platform/ios/Mapbox-iOS-SDK-symbols.podspec
#	platform/ios/Mapbox-iOS-SDK.podspec
#	platform/ios/app/MBXViewController.m
#	src/mbgl/renderer/layers/render_custom_layer.cpp
#	src/mbgl/style/conversion/filter.cpp
#	src/mbgl/style/expression/interpolate.cpp
#	src/mbgl/style/expression/value.cpp
#	test/style/filter.test.cpp

4 files changed, 35 insertions, 53 deletions

diff --git a/include/mbgl/style/conversion/data_driven_property_value.hpp b/include/mbgl/style/conversion/data_driven_property_value.hpp
index 8880d28fb1..07ed201c99 100644
--- a/include/mbgl/style/conversion/data_driven_property_value.hpp
+++ b/include/mbgl/style/conversion/data_driven_property_value.hpp
@@ -4,10 +4,12 @@
 #include <mbgl/style/conversion.hpp>
 #include <mbgl/style/conversion/constant.hpp>
 #include <mbgl/style/conversion/function.hpp>
-#include <mbgl/style/conversion/expression.hpp>
 #include <mbgl/style/expression/is_expression.hpp>
 #include <mbgl/style/expression/is_constant.hpp>
 #include <mbgl/style/expression/find_zoom_curve.hpp>
+#include <mbgl/style/expression/literal.hpp>
+#include <mbgl/style/expression/value.hpp>
+#include <mbgl/style/expression/parsing_context.hpp>
 
 #include <unordered_set>
 
@@ -20,24 +22,35 @@ template <class T>
 struct Converter<DataDrivenPropertyValue<T>> {
 
     optional<DataDrivenPropertyValue<T>> operator()(const Convertible& value, Error& error) const {
+        using namespace mbgl::style::expression;
+        
         if (isUndefined(value)) {
             return DataDrivenPropertyValue<T>();
-        } else if (expression::isExpression(value)) {
-            optional<std::unique_ptr<Expression>> expression = convert<std::unique_ptr<Expression>>(
-                value,
-                error,
-                valueTypeToExpressionType<T>());
-            
+        } else if (isExpression(value)) {
+            ParsingContext ctx(valueTypeToExpressionType<T>());
+            ParseResult expression = ctx.parseLayerPropertyExpression(value);
             if (!expression) {
+                error = { ctx.getCombinedErrors() };
                 return {};
             }
             
-            if (isFeatureConstant(**expression)) {
+            bool featureConstant = isFeatureConstant(**expression);
+            bool zoomConstant = isZoomConstant(**expression);
+            
+            if (featureConstant && !zoomConstant) {
                 return DataDrivenPropertyValue<T>(CameraFunction<T>(std::move(*expression)));
-            } else if (isZoomConstant(**expression)) {
+            } else if (!featureConstant && zoomConstant) {
                 return DataDrivenPropertyValue<T>(SourceFunction<T>(std::move(*expression)));
-            } else {
+            } else if (!featureConstant && !zoomConstant) {
                 return DataDrivenPropertyValue<T>(CompositeFunction<T>(std::move(*expression)));
+            } else {
+                auto literal = dynamic_cast<Literal*>(expression->get());
+                assert(literal);
+                optional<T> constant = fromExpressionValue<T>(literal->getValue());
+                if (!constant) {
+                    return {};
+                }
+                return DataDrivenPropertyValue<T>(*constant);
             }
         } else if (!isObject(value)) {
             optional<T> constant = convert<T>(value, error);
diff --git a/include/mbgl/style/conversion/expression.hpp b/include/mbgl/style/conversion/expression.hpp
deleted file mode 100644
index c5fcf906a7..0000000000
--- a/include/mbgl/style/conversion/expression.hpp
+++ /dev/null
@@ -1,39 +0,0 @@
-#pragma once
-
-#include <mbgl/style/expression/parsing_context.hpp>
-#include <mbgl/style/expression/type.hpp>
-#include <mbgl/style/conversion.hpp>
-
-#include <memory>
-
-namespace mbgl {
-namespace style {
-namespace conversion {
-
-using namespace mbgl::style::expression;
-
-template<> struct Converter<std::unique_ptr<Expression>> {
-    optional<std::unique_ptr<Expression>> operator()(const Convertible& value, Error& error, type::Type expected) const {
-        ParsingContext ctx(optional<type::Type> {expected});
-        ParseResult parsed = ctx.parse(value);
-        if (parsed) {
-            return std::move(*parsed);
-        }
-        std::string combinedError;
-        for (const ParsingError& parsingError : ctx.getErrors()) {
-            if (combinedError.size() > 0) {
-                combinedError += "\n";
-            }
-            if (parsingError.key.size() > 0) {
-                combinedError += parsingError.key + ": ";
-            }
-            combinedError += parsingError.message;
-        }
-        error = { combinedError };
-        return {};
-    };
-};
-
-} // namespace conversion
-} // namespace style
-} // namespace mbgl
diff --git a/include/mbgl/style/conversion/heatmap_color_property_value.hpp b/include/mbgl/style/conversion/heatmap_color_property_value.hpp
index e3689c524c..a4710792d2 100644
--- a/include/mbgl/style/conversion/heatmap_color_property_value.hpp
+++ b/include/mbgl/style/conversion/heatmap_color_property_value.hpp
@@ -4,11 +4,11 @@
 #include <mbgl/style/conversion.hpp>
 #include <mbgl/style/conversion/constant.hpp>
 #include <mbgl/style/conversion/function.hpp>
-#include <mbgl/style/conversion/expression.hpp>
 #include <mbgl/style/expression/value.hpp>
 #include <mbgl/style/expression/is_constant.hpp>
 #include <mbgl/style/expression/is_expression.hpp>
 #include <mbgl/style/expression/find_zoom_curve.hpp>
+#include <mbgl/style/expression/parsing_context.hpp>
 
 namespace mbgl {
 namespace style {
@@ -17,11 +17,14 @@ namespace conversion {
 template <>
 struct Converter<HeatmapColorPropertyValue> {
     optional<HeatmapColorPropertyValue> operator()(const Convertible& value, Error& error) const {
+        using namespace mbgl::style::expression;
         if (isUndefined(value)) {
             return HeatmapColorPropertyValue();
         } else if (isExpression(value)) {
-            optional<std::unique_ptr<Expression>> expression = convert<std::unique_ptr<Expression>>(value, error, expression::type::Color);
+            ParsingContext ctx(type::Color);
+            ParseResult expression = ctx.parseLayerPropertyExpression(value);
             if (!expression) {
+                error = { ctx.getCombinedErrors() };
                 return {};
             }
             assert(*expression);
diff --git a/include/mbgl/style/conversion/property_value.hpp b/include/mbgl/style/conversion/property_value.hpp
index 97117de2ec..3130661f61 100644
--- a/include/mbgl/style/conversion/property_value.hpp
+++ b/include/mbgl/style/conversion/property_value.hpp
@@ -4,11 +4,11 @@
 #include <mbgl/style/conversion.hpp>
 #include <mbgl/style/conversion/constant.hpp>
 #include <mbgl/style/conversion/function.hpp>
-#include <mbgl/style/conversion/expression.hpp>
 #include <mbgl/style/expression/value.hpp>
 #include <mbgl/style/expression/is_constant.hpp>
 #include <mbgl/style/expression/is_expression.hpp>
 #include <mbgl/style/expression/find_zoom_curve.hpp>
+#include <mbgl/style/expression/parsing_context.hpp>
 
 namespace mbgl {
 namespace style {
@@ -17,13 +17,18 @@ namespace conversion {
 template <class T>
 struct Converter<PropertyValue<T>> {
     optional<PropertyValue<T>> operator()(const Convertible& value, Error& error) const {
+        using namespace mbgl::style::expression;
+
         if (isUndefined(value)) {
             return PropertyValue<T>();
         } else if (isExpression(value)) {
-            optional<std::unique_ptr<Expression>> expression = convert<std::unique_ptr<Expression>>(value, error, valueTypeToExpressionType<T>());
+            ParsingContext ctx(valueTypeToExpressionType<T>());
+            ParseResult expression = ctx.parseLayerPropertyExpression(value);
             if (!expression) {
+                error = { ctx.getCombinedErrors() };
                 return {};
             }
+
             if (isFeatureConstant(**expression)) {
                 return { CameraFunction<T>(std::move(*expression)) };
             } else {