Add support for const constraint

include/valijson/constraints/concrete_constraints.hpp

@@ -172,6 +172,34 @@ private:
     const Subschema *elseSubschema;
 };
 
+class ConstConstraint: public BasicConstraint<ConstConstraint>
+{
+public:
+    ConstConstraint()
+      : value(nullptr) { }
+
+    ConstConstraint(CustomAlloc allocFn, CustomFree freeFn)
+      : BasicConstraint(allocFn, freeFn),
+        value(nullptr) { }
+
+    ConstConstraint(const ConstConstraint &other)
+      : BasicConstraint(other),
+        value(other.value->clone()) { }
+
+    adapters::FrozenValue * getValue() const
+    {
+        return value;
+    }
+
+    void setValue(const adapters::Adapter &value)
+    {
+        this->value = value.freeze();
+    }
+
+private:
+    adapters::FrozenValue *value;
+};
+
 /**
  * @brief  Represents a 'contains' constraint
  *

include/valijson/constraints/constraint_visitor.hpp

@@ -6,6 +6,7 @@ namespace constraints {
 class AllOfConstraint;
 class AnyOfConstraint;
 class ConditionalConstraint;
+class ConstConstraint;
 class ContainsConstraint;
 class DependenciesConstraint;
 class EnumConstraint;
@@ -40,6 +41,7 @@ protected:
     typedef constraints::AllOfConstraint AllOfConstraint;
     typedef constraints::AnyOfConstraint AnyOfConstraint;
     typedef constraints::ConditionalConstraint ConditionalConstraint;
+    typedef constraints::ConstConstraint ConstConstraint;
     typedef constraints::ContainsConstraint ContainsConstraint;
     typedef constraints::DependenciesConstraint DependenciesConstraint;
     typedef constraints::EnumConstraint EnumConstraint;
@@ -69,6 +71,7 @@ public:
     virtual bool visit(const AllOfConstraint &) = 0;
     virtual bool visit(const AnyOfConstraint &) = 0;
     virtual bool visit(const ConditionalConstraint &) = 0;
+    virtual bool visit(const ConstConstraint &) = 0;
     virtual bool visit(const ContainsConstraint &) = 0;
     virtual bool visit(const DependenciesConstraint &) = 0;
     virtual bool visit(const EnumConstraint &) = 0;

include/valijson/schema_parser.hpp

@@ -649,6 +649,10 @@ private:
                     &subschema);
         }
 
+        if ((itr = object.find("const")) != object.end()) {
+            rootSchema.addConstraintToSubschema(makeConstConstraint(itr->second), &subschema);
+        }
+
         if ((itr = object.find("contains")) != object.end()) {
             rootSchema.addConstraintToSubschema(
                     makeContainsConstraint(rootSchema, rootNode, itr->second,
@@ -1250,6 +1254,21 @@ private:
         return constraint;
     }
 
+    /**
+     * @brief   Make a new ConstConstraint object.
+     *
+     * @param   node  JSON node containing an arbitrary value
+     *
+     * @return  pointer to a new MinimumConstraint that belongs to the caller
+     */
+    template<typename AdapterType>
+    constraints::ConstConstraint makeConstConstraint(const AdapterType &node)
+    {
+        constraints::ConstConstraint constraint;
+        constraint.setValue(node);
+        return constraint;
+    }
+
     /**
      * @brief   Make a new ContainsConstraint object.
      *

include/valijson/validation_visitor.hpp

@@ -164,7 +164,7 @@ public:
     /**
      * @brief   Validate current node using a set of 'if', 'then' and 'else' subschemas
      *
-     * A conditional constraint allows a document to validated against one of two additional
+     * A conditional constraint allows a document to be validated against one of two additional
      * subschemas (specified via 'then' or 'else' properties) depending on whether the document
      * satifies an optional subschema (specified via the 'if' property).
      *
@@ -182,11 +182,33 @@ public:
             const Subschema *thenSubschema = constraint.getThenSubschema();
             return thenSubschema == nullptr ||
                 thenElseValidator.validateSchema(*thenSubschema);
-        } else {
+        }
+
         const Subschema *elseSubschema = constraint.getElseSubschema();
         return elseSubschema == nullptr ||
             thenElseValidator.validateSchema(*elseSubschema);
     }
+
+    /**
+     * @brief   Validate current node using a 'const' constraint
+     *
+     * A const constraint allows a document to be validated against a specific value.
+     *
+     * @param   constraint  ConstConstraint that the current node must validate against
+     *
+     * @return  \c true if validation passes; \f false otherwise
+     */
+    virtual bool visit(const ConstConstraint &constraint)
+    {
+        if (!constraint.getValue()->equalTo(target, strictTypes)) {
+            if (results) {
+                results->pushError(context,
+                        "Failed to match expected value set by 'const' constraint.");
+            }
+            return false;
+        }
+
+        return true;
     }
 
     /**

tests/test_validator.cpp

@@ -451,12 +451,13 @@ TEST_F(TestValidator, Draft7_BooleanSchema)
     processDraft7TestFile(TEST_SUITE_DIR "draft7/boolean_schema.json");
 }
 
-// TODO: untested const
+TEST_F(TestValidator, Draft7_Const)
+{
+    processDraft7TestFile(TEST_SUITE_DIR "draft7/const.json");
+}
 
 TEST_F(TestValidator, Draft7_Contains)
 {
-    // TODO: currently failing due to missing support for const
-
     processDraft7TestFile(TEST_SUITE_DIR "draft7/contains.json");
 }