From 1bda842fcdc2bdb23c46205fda53d25bc9e9c64a Mon Sep 17 00:00:00 2001
From: Anand Thakker <github@anandthakker.net>
Date: Mon, 21 May 2018 14:20:48 -0400
Subject: [PATCH] Accept constant expressions in non-dds properties

Closes #11940
---
 cmake/test-files.cmake                        |  1 +
 .../mbgl/style/conversion/property_value.hpp  | 14 ++++++++++---
 test/style/conversion/property_value.test.cpp | 21 +++++++++++++++++++
 3 files changed, 33 insertions(+), 3 deletions(-)
 create mode 100644 test/style/conversion/property_value.test.cpp

diff --git a/cmake/test-files.cmake b/cmake/test-files.cmake
index 2aadfa8a7f4..8105cbf5ceb 100644
--- a/cmake/test-files.cmake
+++ b/cmake/test-files.cmake
@@ -79,6 +79,7 @@ set(MBGL_TEST_FILES
     test/style/conversion/geojson_options.test.cpp
     test/style/conversion/layer.test.cpp
     test/style/conversion/light.test.cpp
+    test/style/conversion/property_value.test.cpp
     test/style/conversion/stringify.test.cpp
     test/style/conversion/tileset.test.cpp
 
diff --git a/include/mbgl/style/conversion/property_value.hpp b/include/mbgl/style/conversion/property_value.hpp
index 3130661f61f..dc1c32830f6 100644
--- a/include/mbgl/style/conversion/property_value.hpp
+++ b/include/mbgl/style/conversion/property_value.hpp
@@ -29,11 +29,19 @@ struct Converter<PropertyValue<T>> {
                 return {};
             }
 
-            if (isFeatureConstant(**expression)) {
-                return { CameraFunction<T>(std::move(*expression)) };
-            } else {
+            if (!isFeatureConstant(**expression)) {
                 error = { "property expressions not supported" };
                 return {};
+            } else if (!isZoomConstant(**expression)) {
+                return { CameraFunction<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 PropertyValue<T>(*constant);
             }
         } else if (isObject(value)) {
             optional<CameraFunction<T>> function = convert<CameraFunction<T>>(value, error);
diff --git a/test/style/conversion/property_value.test.cpp b/test/style/conversion/property_value.test.cpp
new file mode 100644
index 00000000000..dcb08bcec7f
--- /dev/null
+++ b/test/style/conversion/property_value.test.cpp
@@ -0,0 +1,21 @@
+#include <mbgl/test/util.hpp>
+
+#include <mbgl/style/conversion/json.hpp>
+#include <mbgl/style/conversion/property_value.hpp>
+#include <mbgl/util/rapidjson.hpp>
+
+using namespace mbgl;
+using namespace mbgl::style;
+using namespace mbgl::style::conversion;
+
+TEST(StyleConversion, PropertyValue) {
+    // PropertyValue<T> accepts a constant expression: https://github.com/mapbox/mapbox-gl-native/issues/11940
+    Error error;
+    JSDocument doc;
+    doc.Parse<0>(R"(["literal", [1, 2]])");
+    auto expected = std::array<float, 2>{{1, 2}};
+    auto result = convert<PropertyValue<std::array<float, 2>>>(doc, error);
+    ASSERT_TRUE(result);
+    ASSERT_TRUE(result->isConstant());
+    ASSERT_EQ(result->asConstant(), expected);
+}