Increase the verbosity of the error message produced when there are undefined references.

src/json-validator.cpp

@@ -14,6 +14,7 @@
 #include <memory>
 #include <set>
 #include <sstream>
+#include <string>
 
 using nlohmann::json;
 using nlohmann::json_patch;
@@ -308,11 +309,31 @@ public:
 				break;
 		} while (1);
 
-		for (const auto &file : files_)
-			if (file.second.unresolved.size() != 0)
+		for (const auto &file : files_) {
+			if (file.second.unresolved.size() != 0) {
+				// Build a representation of the undefined
+				// references as a list of comma-separated strings.
+				auto n_urefs = file.second.unresolved.size();
+				std::string urefs = "[";
+
+				decltype(n_urefs) counter = 0;
+				for (const auto &p : file.second.unresolved) {
+					urefs += p.first;
+
+					if (counter != n_urefs - 1u) {
+						urefs += ", ";
+					}
+
+					++counter;
+				}
+
+				urefs += "]";
+
 				throw std::invalid_argument("after all files have been parsed, '" +
 				                            (file.first == "" ? "<root>" : file.first) +
-				                            "' has still undefined references.");
+				                            "' has still the following undefined references: " + urefs);
+			}
+		}
 	}
 
 	void validate(const json::json_pointer &ptr,

test/issue-98.cpp

@@ -8,7 +8,8 @@ int main(void)
 	try {
 		validator.set_root_schema(nlBase); // this line will log the caught exception
 	} catch (const std::exception &e) {
-		if (std::string("after all files have been parsed, '<root>' has still undefined references.") == e.what())
+
+		if (std::string("after all files have been parsed, '<root>' has still the following undefined references: [/unknown/keywords]") == e.what())
 			return EXIT_SUCCESS;
 	}
 	return EXIT_FAILURE;