Support override of default value when using referenced schemas (#189)

src/json-validator.cpp

@@ -551,9 +551,9 @@ public:
 			sch.erase(attr);
 		}
 
-		const auto defaultAttr = sch.find("default");
-		if (defaultAttr != sch.end()) {
-			defaultValue_ = defaultAttr.value();
+		const auto default_attr = sch.find("default");
+		if (default_attr != sch.end()) {
+			defaultValue_ = default_attr.value();
 		}
 
 		for (auto &key : known_keywords)
@@ -630,6 +630,11 @@ public:
 			sch.erase(attr);
 		}
 	}
+
+	void set_default_value(const json &default_value)
+	{
+		defaultValue_ = default_value;
+	}
 };
 
 class string : public schema
@@ -1276,6 +1281,17 @@ std::shared_ptr<schema> schema::make(json &schema,
 			// so this is the origial URI for this reference, the $ref-value has thus be resolved from it
 			auto id = uris.back().derive(attr.value().get<std::string>());
 			sch = root->get_or_create_ref(id);
+
+			const auto default_attr = schema.find("default");
+			if (default_attr != schema.end()) {
+				if (type_schema *type_sch = dynamic_cast<type_schema *>(sch.get())) {
+					// copy the referenced schema and modify the default value
+					auto schema_copy = std::make_shared<type_schema>(*type_sch);
+					schema_copy->set_default_value(default_attr.value());
+					sch = schema_copy;
+				}
+			}
+
 			schema.erase(attr);
 		} else {
 			sch = std::make_shared<type_schema>(schema, root, uris);

test/CMakeLists.txt

@@ -69,3 +69,7 @@ add_test(NAME binary-validation COMMAND binary-validation)
 add_executable(issue-149-entry-selection issue-149-entry-selection.cpp)
 target_link_libraries(issue-149-entry-selection PRIVATE nlohmann_json_schema_validator)
 add_test(NAME issue-149-entry-selection COMMAND issue-149-entry-selection)
+
+add_executable(issue-189-default-values issue-189-default-values.cpp)
+target_link_libraries(issue-189-default-values nlohmann_json_schema_validator)
+add_test(NAME issue-189-default-values COMMAND issue-189-default-values)

test/issue-189-default-values.cpp

@@ -0,0 +1,50 @@
+#include <iostream>
+#include <nlohmann/json-schema.hpp>
+
+using nlohmann::json;
+using nlohmann::json_schema::json_validator;
+
+static const json rectangle_schema = R"(
+{
+    "$schema": "http://json-schema.org/draft-07/schema#",
+    "title": "A rectangle",
+    "properties": {
+        "width": {
+            "$ref": "#/definitions/length",
+			"default": 20
+        },
+        "height": {
+            "$ref": "#/definitions/length"
+        }
+    },
+	"definitions": {
+        "length": {
+			"type": "integer",
+			"default": 10
+    	}
+	},
+    "additionalProperties": false,
+    "type": "object"
+})"_json;
+
+int main(void)
+{
+	json_validator validator{};
+	validator.set_root_schema(rectangle_schema);
+
+	{
+		json empty_rectangle = R"({})"_json;
+
+		const auto default_patch = validator.validate(empty_rectangle);
+		const auto actual = empty_rectangle.patch(default_patch);
+
+		// height must be 10 according to the default specified in the length definition while width must be 10 overridden by the width element
+		const auto expected = R"({"height":10,"width":20})"_json;
+		if (actual != expected) {
+			std::cerr << "Patch with defaults contains wrong value: '" << actual << "' instead of expected '" << expected.dump() << "'" << std::endl;
+			return 1;
+		}
+	}
+
+	return 0;
+}