ref-schema: create a new ref-schema when default-value is present

Default-values on schemas with a $ref field are now stored within
a new reference schema which links to the original reference schema.
It contains the default value and keeps a strong reference (shared_ptr)
to the original reference.

Fixes #209

src/json-validator.cpp

@@ -65,6 +65,8 @@ class schema_ref : public schema
 {
 	const std::string id_;
 	std::weak_ptr<schema> target_;
+	std::shared_ptr<schema> target_strong_; // for references to references keep also the shared_ptr because
+	                                        // no one else might use it after resolving
 
 	void validate(const json::json_pointer &ptr, const json &instance, json_patch &patch, error_handler &e) const final
 	{
@@ -95,7 +97,13 @@ public:
 	    : schema(root), id_(id) {}
 
 	const std::string &id() const { return id_; }
-	void set_target(const std::shared_ptr<schema> &target) { target_ = target; }
+
+	void set_target(const std::shared_ptr<schema> &target, bool strong = false)
+	{
+		target_ = target;
+		if (strong)
+			target_strong_ = target;
+	}
 };
 
 } // namespace
@@ -1277,13 +1285,17 @@ std::shared_ptr<schema> schema::make(json &schema,
 
 			schema.erase(attr);
 
-			// special case where break draft-7 and allow overriding of properties when a $ref is used
+			// special case where we break draft-7 and allow overriding of properties when a $ref is used
 			attr = schema.find("default");
 			if (attr != schema.end()) {
 				// copy the referenced schema depending on the underlying type and modify the default value
-				if (auto *ref_sch = dynamic_cast<schema_ref *>(sch.get())) {
-					sch = std::make_shared<schema_ref>(*ref_sch);
-					sch->set_default_value(attr.value());
+				if (dynamic_cast<schema_ref *>(sch.get())) {
+					// create a new reference schema use the original reference (which will be resolved later)
+					// to store this overloaed default value #209
+					auto overloaded_ref_sch = std::make_shared<schema_ref>(uris[0].to_string(), root);
+					overloaded_ref_sch->set_target(sch, true);
+					overloaded_ref_sch->set_default_value(attr.value());
+					sch = overloaded_ref_sch;
 				} else if (auto *type_sch = dynamic_cast<type_schema *>(sch.get())) {
 					sch = std::make_shared<type_schema>(*type_sch);
 					sch->set_default_value(attr.value());

test/issue-209/CMakeLists.txt

@@ -0,0 +1,3 @@
+add_test_simple_schema(Issue::209
+                       ${CMAKE_CURRENT_SOURCE_DIR}/entities.schema.json
+                       ${CMAKE_CURRENT_SOURCE_DIR}/instance.json)

test/issue-209/color.schema.json

@@ -0,0 +1,8 @@
+{
+        "$schema": "http://json-schema.org/draft-07/schema#",
+        "$id": "https://example.invalid/color.schema.json",
+        "title": "color",
+        "description": "X11/HTML/CSS color name as a JSON string",
+        "type": "string",
+        "enum": [ "White", "Black", "Red" ]
+}

test/issue-209/entities.schema.json

@@ -0,0 +1,16 @@
+{
+        "$schema": "http://json-schema.org/draft-07/schema#",
+        "$id": "https://example.invalid/entities.schema.json",
+        "title": "Entities",
+        "type": "array",
+        "items": {
+                "type": "object",
+                "required": [ "name" ],
+                "properties": {
+                        "name": {
+                                "type": "string"
+                        },
+                        "fg": { "$ref": "color.schema.json", "default": "Black" }
+                }
+        }
+}

test/issue-209/instance.json

@@ -0,0 +1,10 @@
+[
+        {
+                "name": "player",
+                "fg": "White"
+        },
+        {
+                "name": "enemy",
+                "fg": "Red"
+        }
+]