Relax typing for comparison operators (#12537)

* Relax typing for comparison operators

Ports https://github.com/mapbox/mapbox-gl-js/pull/6961

* Review comments

* Lint fixes

4 files changed, 70 insertions, 36 deletions

diff --git a/include/mbgl/style/expression/comparison.hpp b/include/mbgl/style/expression/comparison.hpp
new file mode 100644
index 0000000000..cf64f5cd34
--- /dev/null
+++ b/include/mbgl/style/expression/comparison.hpp
@@ -0,0 +1,68 @@
+#pragma once
+
+#include <mbgl/style/expression/collator_expression.hpp>
+#include <mbgl/style/expression/expression.hpp>
+#include <mbgl/style/expression/parsing_context.hpp>
+#include <mbgl/style/conversion.hpp>
+
+#include <memory>
+
+namespace mbgl {
+namespace style {
+namespace expression {
+
+ParseResult parseComparison(const mbgl::style::conversion::Convertible&, ParsingContext&);
+
+class BasicComparison : public Expression {
+public:
+    using CompareFunctionType = bool (*) (Value, Value);
+
+    BasicComparison(
+        std::string op,
+        std::unique_ptr<Expression> lhs,
+        std::unique_ptr<Expression> rhs);
+
+    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;
+    std::string getOperator() const override;
+
+private:
+    std::string op;
+    CompareFunctionType compare;
+    std::unique_ptr<Expression> lhs;
+    std::unique_ptr<Expression> rhs;
+    bool needsRuntimeTypeCheck;
+};
+
+class CollatorComparison : public Expression {
+public:
+    using CompareFunctionType = bool (*) (std::string, std::string, Collator);
+
+    CollatorComparison(
+        std::string op,
+        std::unique_ptr<Expression> lhs,
+        std::unique_ptr<Expression> rhs,
+        std::unique_ptr<Expression> collator);
+
+    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;
+    std::string getOperator() const override;
+
+private:
+    std::string op;
+    CompareFunctionType compare;
+    std::unique_ptr<Expression> lhs;
+    std::unique_ptr<Expression> rhs;
+    std::unique_ptr<Expression> collator;
+    bool needsRuntimeTypeCheck;
+};
+
+
+
+} // namespace expression
+} // namespace style
+} // namespace mbgl
diff --git a/include/mbgl/style/expression/dsl.hpp b/include/mbgl/style/expression/dsl.hpp
index e9de20de18..a4483a6fe6 100644
--- a/include/mbgl/style/expression/dsl.hpp
+++ b/include/mbgl/style/expression/dsl.hpp
@@ -31,6 +31,7 @@ std::unique_ptr<Expression> literal(Value value);
 std::unique_ptr<Expression> literal(std::initializer_list<double> value);
 std::unique_ptr<Expression> literal(std::initializer_list<const char *> value);
 
+std::unique_ptr<Expression> assertion(type::Type, std::unique_ptr<Expression>);
 std::unique_ptr<Expression> number(std::unique_ptr<Expression>);
 std::unique_ptr<Expression> string(std::unique_ptr<Expression>);
 std::unique_ptr<Expression> boolean(std::unique_ptr<Expression>);
diff --git a/include/mbgl/style/expression/equals.hpp b/include/mbgl/style/expression/equals.hpp
deleted file mode 100644
index 1e8bf7acef..0000000000
--- a/include/mbgl/style/expression/equals.hpp
+++ /dev/null
@@ -1,35 +0,0 @@
-#pragma once
-
-#include <mbgl/style/expression/collator_expression.hpp>
-#include <mbgl/style/expression/expression.hpp>
-#include <mbgl/style/expression/parsing_context.hpp>
-#include <mbgl/style/conversion.hpp>
-
-#include <memory>
-
-namespace mbgl {
-namespace style {
-namespace expression {
-
-class Equals : public Expression {
-public:
-    Equals(std::unique_ptr<Expression> lhs, std::unique_ptr<Expression> rhs, optional<std::unique_ptr<Expression>> collator, bool negate);
-
-    static ParseResult parse(const mbgl::style::conversion::Convertible&, ParsingContext&);
-
-    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;
-
-    std::string getOperator() const override { return negate ? "!=" : "=="; }
-private:
-    std::unique_ptr<Expression> lhs;
-    std::unique_ptr<Expression> rhs;
-    optional<std::unique_ptr<Expression>> collator;
-    bool negate;
-};
-
-} // namespace expression
-} // namespace style
-} // namespace mbgl
diff --git a/include/mbgl/style/expression/expression.hpp b/include/mbgl/style/expression/expression.hpp
index 8301f1572c..26124f6463 100644
--- a/include/mbgl/style/expression/expression.hpp
+++ b/include/mbgl/style/expression/expression.hpp
@@ -133,7 +133,7 @@ enum class Kind : int32_t {
     Case,
     Any,
     All,
-    Equals,
+    Comparison,
 };
 
 class Expression {