Don't enforce ["zoom"] constraints for filters (#11672)

* Don't enforce ["zoom"] constraints for filters

Fixes #11594

* Add a couple of comments

* Fix ambiguous constructor call

* ParsingContext(optional<Type>) => ParsingContext(Type)

5 files changed, 44 insertions, 59 deletions

diff --git a/include/mbgl/style/conversion/data_driven_property_value.hpp b/include/mbgl/style/conversion/data_driven_property_value.hpp
index b4297816df..07ed201c99 100644
--- a/include/mbgl/style/conversion/data_driven_property_value.hpp
+++ b/include/mbgl/style/conversion/data_driven_property_value.hpp
@@ -4,12 +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>
 
@@ -22,15 +22,15 @@ 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 {};
             }
             
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 {
diff --git a/include/mbgl/style/expression/parsing_context.hpp b/include/mbgl/style/expression/parsing_context.hpp
index f92a4c95ea..c19974a4f7 100644
--- a/include/mbgl/style/expression/parsing_context.hpp
+++ b/include/mbgl/style/expression/parsing_context.hpp
@@ -55,7 +55,7 @@ class ParsingContext {
 public:
     ParsingContext() : errors(std::make_shared<std::vector<ParsingError>>()) {}
     ParsingContext(std::string key_) : key(std::move(key_)), errors(std::make_shared<std::vector<ParsingError>>()) {}
-    explicit ParsingContext(optional<type::Type> expected_)
+    explicit ParsingContext(type::Type expected_)
         : expected(std::move(expected_)),
           errors(std::make_shared<std::vector<ParsingError>>())
     {}
@@ -67,6 +67,7 @@ public:
     std::string getKey() const { return key; }
     optional<type::Type> getExpected() const { return expected; }
     const std::vector<ParsingError>& getErrors() const { return *errors; }
+    const std::string getCombinedErrors() const;
 
     enum TypeAnnotationOption {
         includeTypeAnnotations,
@@ -74,16 +75,21 @@ public:
     };
 
     /*
-        Parse the given style-spec JSON value into an Expression object.
-        Specifically, this function is responsible for determining the expression
-        type (either Literal, or the one named in value[0]) and dispatching to the
-        appropriate ParseXxxx::parse(const V&, ParsingContext) method.
+        Parse the given style-spec JSON value as an expression.
     */
-    ParseResult parse(const mbgl::style::conversion::Convertible& value,
-                      TypeAnnotationOption typeAnnotationOption = includeTypeAnnotations);
+    ParseResult parseExpression(const mbgl::style::conversion::Convertible& value,
+                                TypeAnnotationOption typeAnnotationOption = includeTypeAnnotations);
 
     /*
-        Parse a child expression.
+        Parse the given style-spec JSON value as an expression intended to be used
+        in a layout or paint property.  This entails checking additional constraints
+        that exist in that context but not, e.g., for filters.
+    */
+    ParseResult parseLayerPropertyExpression(const mbgl::style::conversion::Convertible& value,
+                                TypeAnnotationOption typeAnnotationOption = includeTypeAnnotations);
+
+    /*
+        Parse a child expression. For use by individual Expression::parse() methods.
     */
     ParseResult parse(const mbgl::style::conversion::Convertible&,
                       std::size_t,
@@ -91,7 +97,7 @@ public:
                       TypeAnnotationOption typeAnnotationOption = includeTypeAnnotations);
     
     /*
-        Parse a child expression.
+        Parse a child expression.  For use by individual Expression::parse() methods.
     */
     ParseResult parse(const mbgl::style::conversion::Convertible&,
                       std::size_t index,
@@ -141,6 +147,16 @@ private:
         errors(std::move(errors_))
     {}
     
+    
+    /*
+        Parse the given style-spec JSON value into an Expression object.
+        Specifically, this function is responsible for determining the expression
+        type (either Literal, or the one named in value[0]) and dispatching to the
+        appropriate ParseXxxx::parse(const V&, ParsingContext) method.
+    */
+    ParseResult parse(const mbgl::style::conversion::Convertible& value,
+                      TypeAnnotationOption typeAnnotationOption = includeTypeAnnotations);
+    
     std::string key;
     optional<type::Type> expected;
     std::shared_ptr<detail::Scope> scope;