Track expression dependencies (#2113)

include/mbgl/style/color_ramp_property_value.hpp

@@ -24,8 +24,7 @@ class ColorRampPropertyValue {
     }
 
 public:
-    ColorRampPropertyValue()
-        : value(nullptr) {}
+    ColorRampPropertyValue() noexcept = default;
     ColorRampPropertyValue(std::shared_ptr<expression::Expression> value_)
         : value(std::move(value_)) {}
 
@@ -46,6 +45,9 @@ class ColorRampPropertyValue {
     bool hasDataDrivenPropertyDifference(const ColorRampPropertyValue&) const { return false; }
 
     const expression::Expression& getExpression() const { return *value; }
+
+    using Dependency = style::expression::Dependency;
+    Dependency getDependencies() const noexcept { return value ? value->dependencies : Dependency::None; }
 };
 
 } // namespace style

include/mbgl/style/expression/at.hpp

@@ -11,7 +11,7 @@ namespace expression {
 class At : public Expression {
 public:
     At(std::unique_ptr<Expression> index_, std::unique_ptr<Expression> input_)
-        : Expression(Kind::At, input_->getType().get<type::Array>().itemType),
+        : Expression(Kind::At, input_->getType().get<type::Array>().itemType, depsOf(index_) | depsOf(input_)),
           index(std::move(index_)),
           input(std::move(input_)) {}
 

include/mbgl/style/expression/boolean_operator.hpp

@@ -12,7 +12,7 @@ namespace expression {
 class Any : public Expression {
 public:
     Any(std::vector<std::unique_ptr<Expression>> inputs_)
-        : Expression(Kind::Any, type::Boolean),
+        : Expression(Kind::Any, type::Boolean, collectDependencies(inputs_)),
           inputs(std::move(inputs_)) {}
 
     static ParseResult parse(const mbgl::style::conversion::Convertible& value, ParsingContext& ctx);
@@ -31,7 +31,7 @@ class Any : public Expression {
 class All : public Expression {
 public:
     All(std::vector<std::unique_ptr<Expression>> inputs_)
-        : Expression(Kind::All, type::Boolean),
+        : Expression(Kind::All, type::Boolean, collectDependencies(inputs_)),
           inputs(std::move(inputs_)) {}
 
     static ParseResult parse(const mbgl::style::conversion::Convertible& value, ParsingContext& ctx);

include/mbgl/style/expression/case.hpp

@@ -17,7 +17,7 @@ class Case : public Expression {
     using Branch = std::pair<std::unique_ptr<Expression>, std::unique_ptr<Expression>>;
 
     Case(type::Type type_, std::vector<Branch> branches_, std::unique_ptr<Expression> otherwise_)
-        : Expression(Kind::Case, std::move(type_)),
+        : Expression(Kind::Case, std::move(type_), collectDependencies(branches_) | depsOf(otherwise_)),
           branches(std::move(branches_)),
           otherwise(std::move(otherwise_)) {}
 
@@ -32,6 +32,12 @@ class Case : public Expression {
 
     std::string getOperator() const override { return "case"; }
 
+protected:
+    using Expression::collectDependencies;
+    static Dependency collectDependencies(const std::vector<Branch>& branches) {
+        return collectDependencies(branches, [](const Branch& v) { return depsOf(v.first) | depsOf(v.second); });
+    }
+
 private:
     std::vector<Branch> branches;
     std::unique_ptr<Expression> otherwise;

include/mbgl/style/expression/coalesce.hpp

@@ -15,7 +15,7 @@ class Coalesce : public Expression {
 public:
     using Args = std::vector<std::unique_ptr<Expression>>;
     Coalesce(const type::Type& type_, Args args_)
-        : Expression(Kind::Coalesce, type_),
+        : Expression(Kind::Coalesce, type_, collectDependencies(args_)),
           args(std::move(args_)) {}
 
     static ParseResult parse(const mbgl::style::conversion::Convertible& value, ParsingContext& ctx);

include/mbgl/style/expression/coercion.hpp

@@ -12,7 +12,7 @@ namespace expression {
 
 class Coercion : public Expression {
 public:
-    Coercion(type::Type type_, std::vector<std::unique_ptr<Expression>> inputs_);
+    Coercion(const type::Type& type_, std::vector<std::unique_ptr<Expression>> inputs_);
 
     static ParseResult parse(const mbgl::style::conversion::Convertible& value, ParsingContext& ctx);
 

include/mbgl/style/expression/collator_expression.hpp

@@ -21,7 +21,7 @@ class CollatorExpression : public Expression {
 
     void eachChild(const std::function<void(const Expression&)>&) const override;
 
-    bool operator==(const Expression& e) const override;
+    bool operator==(const Expression&) const override;
 
     std::vector<std::optional<Value>> possibleOutputs() const override {
         // Technically the set of possible outputs is the combinatoric set of

include/mbgl/style/expression/error.hpp

@@ -11,7 +11,7 @@ namespace expression {
 class Error : public Expression {
 public:
     Error(std::string message_)
-        : Expression(Kind::Error, type::Error),
+        : Expression(Kind::Error, type::Error, Dependency::None),
           message(std::move(message_)) {}
 
     void eachChild(const std::function<void(const Expression&)>&) const override {}

include/mbgl/style/expression/expression.hpp

@@ -5,12 +5,14 @@
 #include <mbgl/style/expression/value.hpp>
 #include <mbgl/tile/tile_id.hpp>
 #include <mbgl/util/color.hpp>
+#include <mbgl/util/traits.hpp>
 #include <mbgl/util/variant.hpp>
 
 #include <array>
-#include <vector>
 #include <memory>
+#include <numeric>
 #include <optional>
+#include <vector>
 
 namespace mbgl {
 
@@ -135,23 +137,23 @@ class EvaluationResult : public Result<Value> {
 };
 
 /**
-    Expression is an abstract class that serves as an interface and base class
-    for particular expression implementations.
+ Expression is an abstract class that serves as an interface and base class
+ for particular expression implementations.
 
-    CompoundExpression implements the majority of expressions in the spec by
-    inferring the argument and output from a simple function (const T0& arg0,
-    const T1& arg1, ...) -> Result<U> where T0, T1, ..., U are member types of
-    mbgl::style::expression::Value.
+ CompoundExpression implements the majority of expressions in the spec by
+ inferring the argument and output from a simple function (const T0& arg0,
+ const T1& arg1, ...) -> Result<U> where T0, T1, ..., U are member types of
+ mbgl::style::expression::Value.
 
-    The other Expression subclasses (Let, Curve, Match, etc.) exist in order to
-    implement expressions that need specialized parsing, type checking, or
-    evaluation logic that can't be handled by CompoundExpression's inference
-    mechanism.
+ The other Expression subclasses (Let, Curve, Match, etc.) exist in order to
+ implement expressions that need specialized parsing, type checking, or
+ evaluation logic that can't be handled by CompoundExpression's inference
+ mechanism.
 
-    Each Expression subclass also provides a static
-    ParseResult ExpressionClass::parse(const V&, ParsingContext),
-    which handles parsing a style-spec JSON representation of the expression.
-*/
+ Each Expression subclass also provides a static
+ ParseResult ExpressionClass::parse(const V&, ParsingContext),
+ which handles parsing a style-spec JSON representation of the expression.
+ */
 
 enum class Kind : int32_t {
     Coalesce,
@@ -183,10 +185,33 @@ enum class Kind : int32_t {
     Slice
 };
 
+enum class Dependency : uint32_t {
+    None = 0,
+    Feature = 1 << 0,  // Data reference
+    Image = 1 << 1,    // Image reference (equivalent to not "runtime constant")
+    Zoom = 1 << 2,     // Zoom level
+    Location = 1 << 3, // Not used yet, "distance-from-center" not supported
+    Bind = 1 << 4,     // Create variable binding ("let")
+    Var = 1 << 5,      // Use variable binding
+    Override = 1 << 6, // Property override
+    MaskCount = 7,
+};
+inline constexpr static Dependency operator|(Dependency x, Dependency y) noexcept {
+    return Dependency{mbgl::underlying_type(x) | mbgl::underlying_type(y)};
+}
+inline constexpr static Dependency operator&(Dependency x, Dependency y) noexcept {
+    return Dependency{mbgl::underlying_type(x) & mbgl::underlying_type(y)};
+}
+inline static Dependency& operator|=(Dependency& target, Dependency source) noexcept {
+    target = target | source;
+    return target;
+}
+
 class Expression {
 public:
-    Expression(Kind kind_, type::Type type_)
-        : kind(kind_),
+    Expression(Kind kind_, type::Type type_, Dependency dependencies_)
+        : dependencies(dependencies_),
+          kind(kind_),
           type(std::move(type_)) {}
     virtual ~Expression() = default;
 
@@ -195,8 +220,8 @@ class Expression {
     virtual bool operator==(const Expression&) const = 0;
     bool operator!=(const Expression& rhs) const { return !operator==(rhs); }
 
-    Kind getKind() const { return kind; };
-    type::Type getType() const { return type; };
+    Kind getKind() const { return kind; }
+    const type::Type& getType() const { return type; }
 
     EvaluationResult evaluate(std::optional<float> zoom,
                               const Feature& feature,
@@ -229,6 +254,8 @@ class Expression {
 
     virtual std::string getOperator() const = 0;
 
+    const Dependency dependencies;
+
 protected:
     template <typename T>
     static bool childrenEqual(const T& lhs, const T& rhs) {
@@ -261,11 +288,55 @@ class Expression {
         return *(lhs.first) == *(rhs.first) && *(lhs.second) == *(rhs.second);
     }
 
+    static Dependency depsOf(const std::shared_ptr<Expression>& ex) { return ex ? ex->dependencies : Dependency::None; }
+    static Dependency depsOf(const std::unique_ptr<Expression>& ex) { return ex ? ex->dependencies : Dependency::None; }
+
+    template <typename T>
+    static Dependency depsOf(const std::optional<T>& ex) {
+        return ex ? depsOf(*ex) : Dependency::None;
+    }
+
+    /// Combine the dependencies of all the expressions in a container of shared- or unique-pointers to expressions
+    template <typename T>
+    static constexpr Dependency collectDependencies(const std::vector<T>& container) {
+        return std::accumulate(container.begin(), container.end(), Dependency::None, [](auto a, const auto& ex) {
+            return a | depsOf(ex);
+        });
+    }
+
+    template <typename T, typename F>
+    static constexpr Dependency collectDependencies(const std::vector<T>& container, F op) {
+        return std::accumulate(container.begin(), container.end(), Dependency::None, [&](auto a, const auto& item) {
+            return a | op(item);
+        });
+    }
+
+    template <typename K, typename T>
+    static constexpr Dependency collectDependencies(const std::map<K, T>& container) {
+        return std::accumulate(container.begin(), container.end(), Dependency::None, [](auto a, const auto& v) {
+            return a | depsOf(v.second);
+        });
+    }
+
+    template <typename K, typename T>
+    static constexpr Dependency collectDependencies(const std::unordered_map<K, T>& container) {
+        return std::accumulate(container.begin(), container.end(), Dependency::None, [](auto a, const auto& kv) {
+            return a | depsOf(kv.second);
+        });
+    }
+
 private:
     Kind kind;
     type::Type type;
 };
 
 } // namespace expression
 } // namespace style
+
+namespace util {
+std::string toString(style::expression::Dependency);
+} // namespace util
+
+std::ostream& operator<<(std::ostream&, style::expression::Dependency);
+
 } // namespace mbgl

include/mbgl/style/expression/find_zoom_curve.hpp

@@ -1,9 +1,8 @@
 #pragma once
 
-#include <mbgl/style/expression/parsing_context.hpp>
 #include <mbgl/style/expression/interpolate.hpp>
+#include <mbgl/style/expression/parsing_context.hpp>
 #include <mbgl/style/expression/step.hpp>
-
 #include <mbgl/util/variant.hpp>
 
 #include <optional>
@@ -12,9 +11,9 @@ namespace mbgl {
 namespace style {
 namespace expression {
 
-std::optional<variant<const Interpolate*, const Step*, ParsingError>> findZoomCurve(const expression::Expression* e);
+std::optional<variant<const Interpolate*, const Step*, ParsingError>> findZoomCurve(const expression::Expression*);
 
-variant<std::nullptr_t, const Interpolate*, const Step*> findZoomCurveChecked(const expression::Expression* e);
+variant<std::nullptr_t, const Interpolate*, const Step*> findZoomCurveChecked(const expression::Expression&);
 
 } // namespace expression
 } // namespace style

include/mbgl/style/expression/format_expression.hpp

@@ -10,17 +10,17 @@ namespace expression {
 struct FormatExpressionSection {
     explicit FormatExpressionSection(std::unique_ptr<Expression> content_);
 
-    void setTextSectionOptions(std::optional<std::unique_ptr<Expression>> fontScale_,
-                               std::optional<std::unique_ptr<Expression>> textFont_,
-                               std::optional<std::unique_ptr<Expression>> textColor_);
+    void setTextSectionOptions(std::unique_ptr<Expression>&& fontScale_,
+                               std::unique_ptr<Expression>&& textFont_,
+                               std::unique_ptr<Expression>&& textColor_);
 
     // Content can be expression that evaluates to String or Image.
     std::shared_ptr<Expression> content;
 
     // Text related section options.
-    std::optional<std::shared_ptr<Expression>> fontScale;
-    std::optional<std::shared_ptr<Expression>> textFont;
-    std::optional<std::shared_ptr<Expression>> textColor;
+    std::shared_ptr<Expression> fontScale;
+    std::shared_ptr<Expression> textFont;
+    std::shared_ptr<Expression> textColor;
 };
 
 class FormatExpression final : public Expression {
@@ -45,6 +45,11 @@ class FormatExpression final : public Expression {
     mbgl::Value serialize() const override;
     std::string getOperator() const override { return "format"; }
 
+private:
+    static Dependency depsOfSection(const FormatExpressionSection& s) {
+        return depsOf(s.content) | depsOf(s.fontScale) | depsOf(s.textFont) | depsOf(s.textColor);
+    }
+
 private:
     std::vector<FormatExpressionSection> sections;
 };

include/mbgl/style/expression/format_section_override.hpp

@@ -13,7 +13,9 @@ class FormatSectionOverride final : public Expression {
     FormatSectionOverride(const type::Type& type_,
                           PossiblyEvaluatedPropertyValue<T> defaultValue_,
                           std::string propertyName_)
-        : Expression(Kind::FormatSectionOverride, type_),
+        : Expression(Kind::FormatSectionOverride,
+                     type_,
+                     defaultValue_.getDependencies() | Dependency::Override | Dependency::Feature),
           defaultValue(std::move(defaultValue_)),
           propertyName(std::move(propertyName_)) {}
 

include/mbgl/style/expression/let.hpp

@@ -17,7 +17,7 @@ class Let : public Expression {
     using Bindings = std::map<std::string, std::shared_ptr<Expression>>;
 
     Let(Bindings bindings_, std::unique_ptr<Expression> result_)
-        : Expression(Kind::Let, result_->getType()),
+        : Expression(Kind::Let, result_->getType(), collectDependencies(bindings_) | Dependency::Bind),
           bindings(std::move(bindings_)),
           result(std::move(result_)) {}
 
@@ -49,7 +49,7 @@ class Let : public Expression {
 class Var : public Expression {
 public:
     Var(std::string name_, std::shared_ptr<Expression> value_)
-        : Expression(Kind::Var, value_->getType()),
+        : Expression(Kind::Var, value_->getType(), depsOf(value_) | Dependency::Var),
           name(std::move(name_)),
           value(std::move(value_)) {}
 

include/mbgl/style/expression/literal.hpp

@@ -13,11 +13,11 @@ namespace expression {
 class Literal : public Expression {
 public:
     Literal(const Value& value_)
-        : Expression(Kind::Literal, typeOf(value_)),
+        : Expression(Kind::Literal, typeOf(value_), Dependency::None),
           value(value_) {}
 
     Literal(const type::Array& type_, std::vector<Value> value_)
-        : Expression(Kind::Literal, type_),
+        : Expression(Kind::Literal, type_, Dependency::None),
           value(std::move(value_)) {}
 
     EvaluationResult evaluate(const EvaluationContext&) const override { return value; }

include/mbgl/style/expression/match.hpp

@@ -19,7 +19,7 @@ class Match : public Expression {
           std::unique_ptr<Expression> input_,
           Branches branches_,
           std::unique_ptr<Expression> otherwise_)
-        : Expression(Kind::Match, type_),
+        : Expression(Kind::Match, type_, depsOf(input_) | depsOf(otherwise_) | collectDependencies(branches_)),
           input(std::move(input_)),
           branches(std::move(branches_)),
           otherwise(std::move(otherwise_)) {}