Expose loot-condition-interpreter error codes to callers

Make ConditionSyntaxError extend from system_error instead of directly from runtime_error, so that callers can use the exception's code to distinguish between different causes.

include/loot/exception/condition_syntax_error.h

@@ -32,9 +32,9 @@ namespace loot {
  * @brief An exception class thrown if invalid syntax is encountered when
  *        parsing a metadata condition.
  */
-class ConditionSyntaxError : public std::runtime_error {
+class ConditionSyntaxError : public std::system_error {
 public:
-  using std::runtime_error::runtime_error;
+  using std::system_error::system_error;
 };
 }
 

include/loot/exception/error_categories.h

@@ -45,6 +45,14 @@ LOOT_API const std::error_category& esplugin_category();
  *          derived from std::error_category.
  */
 LOOT_API const std::error_category& libloadorder_category();
+
+/**
+ * @brief Get the error category that can be used to identify system_error
+ *        exceptions that are due to loot condition interpreter errors.
+ * @returns A reference to the static object of unspecified runtime type,
+ *          derived from std::error_category.
+ */
+LOOT_API const std::error_category& loot_condition_interpreter_category();
 }
 
 #endif

src/api/error_categories.cpp

@@ -47,6 +47,16 @@ class libloadorder_category : public std::error_category {
     return code.category().name() == name();
   }
 };
+
+class loot_condition_interpreter_category : public std::error_category {
+  const char* name() const noexcept override { return "loot condition interpreter"; }
+
+  std::string message(int) const override { return "loot condition interpreter error"; }
+
+  bool equivalent(const std::error_code& code, int) const noexcept override {
+    return code.category().name() == name();
+  }
+};
 }
 
 LOOT_API const std::error_category& esplugin_category() {
@@ -58,4 +68,9 @@ LOOT_API const std::error_category& libloadorder_category() {
   static detail::libloadorder_category instance;
   return instance;
 }
+
+LOOT_API const std::error_category& loot_condition_interpreter_category() {
+  static detail::loot_condition_interpreter_category instance;
+  return instance;
+}
 }

src/api/metadata/condition_evaluator.cpp

@@ -29,6 +29,7 @@
 #include "api/helpers/crc.h"
 #include "api/helpers/logging.h"
 #include "loot/exception/condition_syntax_error.h"
+#include "loot/exception/error_categories.h"
 
 namespace loot {
 void HandleError(const std::string operation, int returnCode) {
@@ -50,7 +51,7 @@ void HandleError(const std::string operation, int returnCode) {
     logger->error(err);
   }
 
-  throw ConditionSyntaxError(err);
+  throw ConditionSyntaxError(returnCode, loot_condition_interpreter_category(), err);
 }
 
 int mapGameType(GameType gameType) {