[core, ios, macos, android] Add data-driven-styling support for `text-font`

22 files changed, 94 insertions, 22 deletions

diff --git a/include/mbgl/style/expression/array_assertion.hpp b/include/mbgl/style/expression/array_assertion.hpp
index 2516eea024..7f36f8aac2 100644
--- a/include/mbgl/style/expression/array_assertion.hpp
+++ b/include/mbgl/style/expression/array_assertion.hpp
@@ -30,6 +30,10 @@ public:
         return false;
     }
 
+    std::vector<optional<Value>> possibleOutputs() const override {
+        return input->possibleOutputs();
+    }
+
 private:
     std::unique_ptr<Expression> input;
 };
diff --git a/include/mbgl/style/expression/assertion.hpp b/include/mbgl/style/expression/assertion.hpp
index 504d49f4e5..43ea73f2ba 100644
--- a/include/mbgl/style/expression/assertion.hpp
+++ b/include/mbgl/style/expression/assertion.hpp
@@ -1,7 +1,9 @@
 #pragma once
+
 #include <mbgl/style/expression/expression.hpp>
 #include <mbgl/style/conversion.hpp>
 #include <mbgl/style/expression/parsing_context.hpp>
+
 #include <memory>
 #include <vector>
 
@@ -23,6 +25,8 @@ public:
     
     bool operator==(const Expression& e) const override;
 
+    std::vector<optional<Value>> possibleOutputs() const override;
+
 private:
     std::vector<std::unique_ptr<Expression>> inputs;
 };
@@ -30,4 +34,3 @@ private:
 } // namespace expression
 } // namespace style
 } // namespace mbgl
-
diff --git a/include/mbgl/style/expression/at.hpp b/include/mbgl/style/expression/at.hpp
index e3eefa4fe8..27fccc761f 100644
--- a/include/mbgl/style/expression/at.hpp
+++ b/include/mbgl/style/expression/at.hpp
@@ -28,6 +28,10 @@ public:
         return false;
     }
 
+    std::vector<optional<Value>> possibleOutputs() const override {
+        return { nullopt };
+    }
+
 private:
     std::unique_ptr<Expression> index;
     std::unique_ptr<Expression> input;
diff --git a/include/mbgl/style/expression/boolean_operator.hpp b/include/mbgl/style/expression/boolean_operator.hpp
index 01231d706b..115a096665 100644
--- a/include/mbgl/style/expression/boolean_operator.hpp
+++ b/include/mbgl/style/expression/boolean_operator.hpp
@@ -2,6 +2,7 @@
 
 #include <mbgl/style/expression/expression.hpp>
 #include <mbgl/style/conversion.hpp>
+
 #include <memory>
 
 namespace mbgl {
@@ -20,6 +21,7 @@ public:
     EvaluationResult evaluate(const EvaluationContext& params) const override;
     void eachChild(const std::function<void(const Expression&)>& visit) const override;
     bool operator==(const Expression& e) const override;
+    std::vector<optional<Value>> possibleOutputs() const override;
 
 private:
     std::vector<std::unique_ptr<Expression>> inputs;
@@ -36,8 +38,8 @@ public:
 
     EvaluationResult evaluate(const EvaluationContext& params) const override;
     void eachChild(const std::function<void(const Expression&)>& visit) const override;
-
     bool operator==(const Expression& e) const override;
+    std::vector<optional<Value>> possibleOutputs() const override;
 
 private:
     std::vector<std::unique_ptr<Expression>> inputs;
@@ -46,4 +48,3 @@ private:
 } // namespace expression
 } // namespace style
 } // namespace mbgl
-
diff --git a/include/mbgl/style/expression/case.hpp b/include/mbgl/style/expression/case.hpp
index ece2fe0329..e61a55fc6d 100644
--- a/include/mbgl/style/expression/case.hpp
+++ b/include/mbgl/style/expression/case.hpp
@@ -26,6 +26,8 @@ public:
     
     bool operator==(const Expression& e) const override;
 
+    std::vector<optional<Value>> possibleOutputs() const override;
+
 private:
     std::vector<Branch> branches;
     std::unique_ptr<Expression> otherwise;
diff --git a/include/mbgl/style/expression/coalesce.hpp b/include/mbgl/style/expression/coalesce.hpp
index 4e6a9b3793..52d9498cbd 100644
--- a/include/mbgl/style/expression/coalesce.hpp
+++ b/include/mbgl/style/expression/coalesce.hpp
@@ -27,7 +27,9 @@ public:
     void eachChild(const std::function<void(const Expression&)>& visit) const override;
 
     bool operator==(const Expression& e) const override;
-    
+
+    std::vector<optional<Value>> possibleOutputs() const override;
+
     std::size_t getLength() const {
         return args.size();
     }
diff --git a/include/mbgl/style/expression/coercion.hpp b/include/mbgl/style/expression/coercion.hpp
index 665bb7ce7c..40d2490186 100644
--- a/include/mbgl/style/expression/coercion.hpp
+++ b/include/mbgl/style/expression/coercion.hpp
@@ -1,6 +1,8 @@
 #pragma once
+
 #include <mbgl/style/expression/expression.hpp>
 #include <mbgl/style/conversion.hpp>
+
 #include <memory>
 #include <vector>
 
@@ -23,6 +25,9 @@ public:
     void eachChild(const std::function<void(const Expression&)>& visit) const override;
 
     bool operator==(const Expression& e) const override;
+
+    std::vector<optional<Value>> possibleOutputs() const override;
+
 private:
     EvaluationResult (*coerceSingleValue) (const Value& v);
     std::vector<std::unique_ptr<Expression>> inputs;
diff --git a/include/mbgl/style/expression/compound_expression.hpp b/include/mbgl/style/expression/compound_expression.hpp
index fc3edbfd4a..8b74027578 100644
--- a/include/mbgl/style/expression/compound_expression.hpp
+++ b/include/mbgl/style/expression/compound_expression.hpp
@@ -72,7 +72,11 @@ public:
             [&](const std::vector<type::Type>& p) -> optional<std::size_t> { return p.size(); }
         );
     }
-    
+
+    std::vector<optional<Value>> possibleOutputs() const override {
+        return { nullopt };
+    }
+
 private:
     std::string name;
     variant<std::vector<type::Type>, VarargsType> params;
@@ -107,7 +111,7 @@ public:
         }
         return false;
     }
-    
+
 private:
     Signature signature;
     typename Signature::Args args;
diff --git a/include/mbgl/style/expression/equals.hpp b/include/mbgl/style/expression/equals.hpp
index 3c0c024294..80550bd59d 100644
--- a/include/mbgl/style/expression/equals.hpp
+++ b/include/mbgl/style/expression/equals.hpp
@@ -19,6 +19,7 @@ public:
     void eachChild(const std::function<void(const Expression&)>& visit) const override;
     bool operator==(const Expression&) const override;
     EvaluationResult evaluate(const EvaluationContext&) const override;
+    std::vector<optional<Value>> possibleOutputs() const override;
 
 private:
     std::unique_ptr<Expression> lhs;
diff --git a/include/mbgl/style/expression/expression.hpp b/include/mbgl/style/expression/expression.hpp
index a22fc28724..cf9fa0cb21 100644
--- a/include/mbgl/style/expression/expression.hpp
+++ b/include/mbgl/style/expression/expression.hpp
@@ -1,8 +1,5 @@
 #pragma once
 
-#include <array>
-#include <vector>
-#include <memory>
 #include <mbgl/util/optional.hpp>
 #include <mbgl/util/variant.hpp>
 #include <mbgl/util/color.hpp>
@@ -10,6 +7,10 @@
 #include <mbgl/style/expression/value.hpp>
 #include <mbgl/style/expression/parsing_context.hpp>
 
+#include <array>
+#include <vector>
+#include <memory>
+
 namespace mbgl {
 
 class GeometryTileFeature;
@@ -38,7 +39,7 @@ public:
     optional<double> heatmapDensity;
 };
 
-template<typename T>
+template <typename T>
 class Result : private variant<EvaluationError, T> {
 public:
     using variant<EvaluationError, T>::variant;
@@ -128,6 +129,13 @@ public:
     
     EvaluationResult evaluate(optional<float> zoom, const Feature& feature, optional<double> heatmapDensity) const;
 
+    /**
+     * Statically analyze the expression, attempting to enumerate possible outputs. Returns
+     * an array of values plus the sentinel null optional value, used to indicate that the
+     * complete set of outputs is statically undecidable.
+     */
+    virtual std::vector<optional<Value>> possibleOutputs() const = 0;
+
 protected:
     template <typename T>
     static bool childrenEqual(const T& lhs, const T& rhs) {
@@ -161,8 +169,6 @@ protected:
                            const std::pair<std::unique_ptr<Expression>, std::unique_ptr<Expression>>& rhs) {
         return *(lhs.first) == *(rhs.first) && *(lhs.second) == *(rhs.second);
     }
-    
-    
 
 private:
     type::Type type;
diff --git a/include/mbgl/style/expression/interpolate.hpp b/include/mbgl/style/expression/interpolate.hpp
index fd9ec25a2c..c82c04bbb0 100644
--- a/include/mbgl/style/expression/interpolate.hpp
+++ b/include/mbgl/style/expression/interpolate.hpp
@@ -89,6 +89,8 @@ public:
         );
     }
 
+    std::vector<optional<Value>> possibleOutputs() const override;
+
 protected:
     const Interpolator interpolator;
     const std::unique_ptr<Expression> input;
diff --git a/include/mbgl/style/expression/let.hpp b/include/mbgl/style/expression/let.hpp
index aaa16ca0c2..6829ded9b8 100644
--- a/include/mbgl/style/expression/let.hpp
+++ b/include/mbgl/style/expression/let.hpp
@@ -33,6 +33,8 @@ public:
         return false;
     }
 
+    std::vector<optional<Value>> possibleOutputs() const override;
+
     Expression* getResult() const {
         return result.get();
     }
@@ -61,7 +63,9 @@ public:
         }
         return false;
     }
-    
+
+    std::vector<optional<Value>> possibleOutputs() const override;
+
 private:
     std::string name;
     std::shared_ptr<Expression> value;
diff --git a/include/mbgl/style/expression/literal.hpp b/include/mbgl/style/expression/literal.hpp
index a0819c7e73..82983d78af 100644
--- a/include/mbgl/style/expression/literal.hpp
+++ b/include/mbgl/style/expression/literal.hpp
@@ -28,7 +28,11 @@ public:
         }
         return false;
     }
-    
+
+    std::vector<optional<Value>> possibleOutputs() const override {
+        return {{ value }};
+    }
+
 private:
     Value value;
 };
diff --git a/include/mbgl/style/expression/match.hpp b/include/mbgl/style/expression/match.hpp
index e17fe96bfe..682d784b0f 100644
--- a/include/mbgl/style/expression/match.hpp
+++ b/include/mbgl/style/expression/match.hpp
@@ -25,14 +25,15 @@ public:
         otherwise(std::move(otherwise_))
     {}
 
+    EvaluationResult evaluate(const EvaluationContext& params) const override;
+
     void eachChild(const std::function<void(const Expression&)>& visit) const override;
 
     bool operator==(const Expression& e) const override;
 
-    EvaluationResult evaluate(const EvaluationContext& params) const override;
-    
+    std::vector<optional<Value>> possibleOutputs() const override;
+
 private:
-    
     std::unique_ptr<Expression> input;
     Branches branches;
     std::unique_ptr<Expression> otherwise;
diff --git a/include/mbgl/style/expression/step.hpp b/include/mbgl/style/expression/step.hpp
index e3c49bc609..4a0a724d7c 100644
--- a/include/mbgl/style/expression/step.hpp
+++ b/include/mbgl/style/expression/step.hpp
@@ -33,6 +33,8 @@ public:
 
     bool operator==(const Expression& e) const override;
 
+    std::vector<optional<Value>> possibleOutputs() const override;
+
     static ParseResult parse(const mbgl::style::conversion::Convertible& value, ParsingContext& ctx);
 
 private:
diff --git a/include/mbgl/style/expression/value.hpp b/include/mbgl/style/expression/value.hpp
index 8baa9d2dba..be5be64752 100644
--- a/include/mbgl/style/expression/value.hpp
+++ b/include/mbgl/style/expression/value.hpp
@@ -148,6 +148,15 @@ struct ValueConverter<T, std::enable_if_t< std::is_enum<T>::value >> {
     static optional<T> fromExpressionValue(const Value& value);
 };
 
+template <typename T>
+std::vector<optional<T>> fromExpressionValues(const std::vector<optional<Value>>& values) {
+    std::vector<optional<T>> result;
+    for (const auto& value : values) {
+        result.push_back(value ? fromExpressionValue<T>(*value) : nullopt);
+    }
+    return result;
+}
+
 } // namespace expression
 } // namespace style
 } // namespace mbgl
diff --git a/include/mbgl/style/function/camera_function.hpp b/include/mbgl/style/function/camera_function.hpp
index 25b38e3616..015abd3e62 100644
--- a/include/mbgl/style/function/camera_function.hpp
+++ b/include/mbgl/style/function/camera_function.hpp
@@ -12,7 +12,6 @@
 #include <mbgl/util/interpolate.hpp>
 #include <mbgl/util/variant.hpp>
 
-
 namespace mbgl {
 namespace style {
 
@@ -66,7 +65,11 @@ public:
             [&](auto z) { return z->getCoveringStops(lower, upper); }
         );
     }
-    
+
+    std::vector<optional<T>> possibleOutputs() const {
+        return expression::fromExpressionValues<T>(expression->possibleOutputs());
+    }
+
     friend bool operator==(const CameraFunction& lhs,
                            const CameraFunction& rhs) {
         return *lhs.expression == *rhs.expression;
diff --git a/include/mbgl/style/function/composite_function.hpp b/include/mbgl/style/function/composite_function.hpp
index b44bf8e6fe..24578f599c 100644
--- a/include/mbgl/style/function/composite_function.hpp
+++ b/include/mbgl/style/function/composite_function.hpp
@@ -102,6 +102,10 @@ public:
         );
     }
 
+    std::vector<optional<T>> possibleOutputs() const {
+        return expression::fromExpressionValues<T>(expression->possibleOutputs());
+    }
+
     friend bool operator==(const CompositeFunction& lhs,
                            const CompositeFunction& rhs) {
         return *lhs.expression == *rhs.expression;
diff --git a/include/mbgl/style/function/convert.hpp b/include/mbgl/style/function/convert.hpp
index 9f7b7ed1f8..8e544d3ad5 100644
--- a/include/mbgl/style/function/convert.hpp
+++ b/include/mbgl/style/function/convert.hpp
@@ -45,6 +45,10 @@ public:
         return EvaluationError{message};
     }
 
+    std::vector<optional<Value>> possibleOutputs() const override {
+        return {};
+    }
+
 private:
     std::string message;
 };
diff --git a/include/mbgl/style/function/source_function.hpp b/include/mbgl/style/function/source_function.hpp
index 02e4b604e2..bd7b109fd8 100644
--- a/include/mbgl/style/function/source_function.hpp
+++ b/include/mbgl/style/function/source_function.hpp
@@ -57,6 +57,10 @@ public:
         return defaultValue ? *defaultValue : finalDefaultValue;
     }
 
+    std::vector<optional<T>> possibleOutputs() const {
+        return expression::fromExpressionValues<T>(expression->possibleOutputs());
+    }
+
     friend bool operator==(const SourceFunction& lhs,
                            const SourceFunction& rhs) {
         return *lhs.expression == *rhs.expression;
diff --git a/include/mbgl/style/layers/symbol_layer.hpp b/include/mbgl/style/layers/symbol_layer.hpp
index a72baa0b4e..f068e2d060 100644
--- a/include/mbgl/style/layers/symbol_layer.hpp
+++ b/include/mbgl/style/layers/symbol_layer.hpp
@@ -118,9 +118,9 @@ public:
     DataDrivenPropertyValue<std::string> getTextField() const;
     void setTextField(DataDrivenPropertyValue<std::string>);
 
-    static PropertyValue<std::vector<std::string>> getDefaultTextFont();
-    PropertyValue<std::vector<std::string>> getTextFont() const;
-    void setTextFont(PropertyValue<std::vector<std::string>>);
+    static DataDrivenPropertyValue<std::vector<std::string>> getDefaultTextFont();
+    DataDrivenPropertyValue<std::vector<std::string>> getTextFont() const;
+    void setTextFont(DataDrivenPropertyValue<std::vector<std::string>>);
 
     static DataDrivenPropertyValue<float> getDefaultTextSize();
     DataDrivenPropertyValue<float> getTextSize() const;
diff --git a/include/mbgl/util/optional.hpp b/include/mbgl/util/optional.hpp
index a9374a1b53..abec02dca9 100644
--- a/include/mbgl/util/optional.hpp
+++ b/include/mbgl/util/optional.hpp
@@ -7,4 +7,7 @@ namespace mbgl {
 template <typename T>
 using optional = std::experimental::optional<T>;
 
+using nullopt_t = std::experimental::nullopt_t;
+constexpr nullopt_t nullopt = std::experimental::nullopt;
+
 } // namespace mbgl