error-messages: Numeric limit errors should show maximum precision

Fixes #255

src/json-validator.cpp

@@ -877,22 +877,31 @@ class numeric : public schema
 	{
 		T value = instance; // conversion of json to value_type
 
+		std::ostringstream oss;
+
 		if (multipleOf_.first && value != 0) // zero is multiple of everything
 			if (violates_multiple_of(value))
-				e.error(ptr, instance, "instance is not a multiple of " + std::to_string(multipleOf_.second));
+				oss << "instance is not a multiple of " << json(multipleOf_.second);
 
 		if (maximum_.first) {
 			if (exclusiveMaximum_ && value >= maximum_.second)
-				e.error(ptr, instance, "instance exceeds or equals maximum of " + std::to_string(maximum_.second));
+				oss << "instance exceeds or equals maximum of " << json(maximum_.second);
 			else if (value > maximum_.second)
-				e.error(ptr, instance, "instance exceeds maximum of " + std::to_string(maximum_.second));
+				oss << "instance exceeds maximum of " << json(maximum_.second);
 		}
 
 		if (minimum_.first) {
 			if (exclusiveMinimum_ && value <= minimum_.second)
-				e.error(ptr, instance, "instance is below or equals minimum of " + std::to_string(minimum_.second));
+				oss << "instance is below or equals minimum of " << json(minimum_.second);
 			else if (value < minimum_.second)
-				e.error(ptr, instance, "instance is below minimum of " + std::to_string(minimum_.second));
+				oss << "instance is below minimum of " << json(minimum_.second);
+		}
+
+		oss.seekp(0, std::ios::end);
+		auto size = oss.tellp();
+		if (size != 0) {
+		    oss.seekp(0, std::ios::beg);
+			e.error(ptr, instance, oss.str());
 		}
 	}
 

test/CMakeLists.txt

@@ -85,3 +85,7 @@ add_test(NAME issue-229-oneof-default-values COMMAND issue-229-oneof-default-val
 add_executable(issue-243-root-default-values issue-243-root-default-values.cpp)
 target_link_libraries(issue-243-root-default-values nlohmann_json_schema_validator)
 add_test(NAME issue-243-root-default-values COMMAND issue-243-root-default-values)
+
+add_executable(issue-255-error-message-limit-precision issue-255-error-message-limit-precision.cpp)
+target_link_libraries(issue-255-error-message-limit-precision nlohmann_json_schema_validator)
+add_test(NAME issue-255-error-message-limit-precision COMMAND issue-255-error-message-limit-precision)

test/issue-255-error-message-limit-precision.cpp

@@ -0,0 +1,41 @@
+#include <nlohmann/json-schema.hpp>
+#include <stdexcept>
+
+using nlohmann::json;
+using nlohmann::json_schema::json_validator;
+
+static const json schema = R"(
+{
+  "$schema": "http://json-schema.org/draft-07/schema#",
+  "$id": "arc.schema.json",
+  "properties": {
+    "angle": {
+      "type": "number",
+      "description": "Radians, from -π to π.",
+      "minimum": -3.14159265358979323846,
+      "maximum": 3.14159265358979323846
+    }
+  }
+})"_json;
+
+class custom_error_handler : public nlohmann::json_schema::basic_error_handler
+{
+	void error(const nlohmann::json::json_pointer &ptr, const json &instance, const std::string &message) override
+	{
+        if (message != "instance exceeds maximum of 3.141592653589793")
+            throw std::invalid_argument("Precision print does not work.");
+	}
+};
+
+int main(void)
+{
+	json_validator validator;
+
+    auto instance = R"({ "angle": 3.1415927410125732 })"_json;
+
+	validator.set_root_schema(schema);
+	custom_error_handler err;
+	validator.validate(instance, err);
+
+	return 0;
+}