Implement Expressions (#9439)

Ports https://github.com/mapbox/mapbox-gl-js/pull/4777 (and its several follow-ups)

1 files changed, 28 insertions, 0 deletions

diff --git a/test/style/conversion/function.test.cpp b/test/style/conversion/function.test.cpp
index 9e8a6b3a7f..a48be2c075 100644
--- a/test/style/conversion/function.test.cpp
+++ b/test/style/conversion/function.test.cpp
@@ -3,6 +3,8 @@
 #include <mbgl/style/conversion/json.hpp>
 #include <mbgl/style/conversion/constant.hpp>
 #include <mbgl/style/conversion/function.hpp>
+#include <mbgl/style/conversion/data_driven_property_value.hpp>
+#include <mbgl/util/rapidjson.hpp>
 
 using namespace mbgl;
 using namespace mbgl::style;
@@ -50,3 +52,29 @@ TEST(StyleConversion, Function) {
     ASSERT_FALSE(fn9);
     ASSERT_EQ("function base must be a number", error.message);
 }
+
+TEST(StyleConversion, CompositeFunctionExpression) {
+    Error error;
+
+    auto parseFunction = [&](const std::string& src) {
+        JSDocument doc;
+        doc.Parse<0>(src);
+        return convert<DataDrivenPropertyValue<float>>(doc, error);
+    };
+
+    auto fn1 = parseFunction(R"(["interpolate", ["linear"], ["zoom"], 0, ["number", ["get", "x"]], 10, 10])");
+    ASSERT_TRUE(fn1);
+    
+    auto fn2 = parseFunction(R"(["coalesce", ["interpolate", ["linear"], ["zoom"], 0, ["number", ["get", "x"]], 10, 10], 0])");
+    ASSERT_TRUE(fn2);
+
+    auto fn3 = parseFunction(R"(["let", "a", 0, ["interpolate", ["linear"], ["zoom"], 0, ["number", ["get", "x"]], 10, 10] ])");
+    ASSERT_TRUE(fn3);
+
+    auto fn4 = parseFunction(R"(["coalesce", ["let", "a", 0, ["interpolate", ["linear"], ["zoom"], 0, ["number", ["get", "x"]], 10, 10], 0 ])");
+    ASSERT_TRUE(fn4);
+
+    auto fn5 = parseFunction(R"(["coalesce", ["interpolate", ["linear"], ["number", ["get", "x"]], 0, ["zoom"], 10, 10], 0])");
+    ASSERT_FALSE(fn5);
+    ASSERT_EQ(R"("zoom" expression may only be used as input to a top-level "step" or "interpolate" expression.)", error.message);
+}