vars: Throw ReadOnlyVariableError when setting read-only var

bindings/libdnf5/conf.i

@@ -106,6 +106,7 @@ wrap_unique_ptr(StringUniquePtr, std::string);
 %ignore ConfigParserOptionNotFoundError;
 %include "libdnf5/conf/config_parser.hpp"
 
+%ignore libdnf5::ReadOnlyVariableError;
 %include "libdnf5/conf/vars.hpp"
 
 %include "libdnf5/conf/config.hpp"

include/libdnf5/conf/vars.hpp

@@ -29,6 +29,14 @@ along with libdnf. If not, see <https://www.gnu.org/licenses/>.
 
 namespace libdnf5 {
 
+// Thrown when attempting to set a read-only variable
+class ReadOnlyVariableError : public Error {
+ using Error::Error;
+
+ const char * get_domain_name() const noexcept override { return "libdnf5"; }
+ const char * get_name() const noexcept override { return "ReadOnlyVariableError"; }
+};
+
 /// @class Vars
 ///
 /// @brief Class for reading and substituting DNF vars (arch, releasever, etc.).
@@ -68,6 +76,7 @@ struct Vars {
  /// @param name Name of the variable
  /// @param value Value to be stored in variable
  /// @param prio Source/Priority of the value
+ /// @throw ReadOnlyVariableError if the variable is read-only
  void set(const std::string & name, const std::string & value, Priority prio = Priority::RUNTIME);
 
  /// @brief Checks whether a variable is read-only
@@ -132,6 +141,7 @@ struct Vars {
  /// @param name Name of the variable
  /// @param get_value Function that returns the (optional) value for the variable
  /// @param prio Source/Priority of the value
+ /// @throw ReadOnlyVariableError if the variable is read-only
  void set_lazy(
  const std::string & name,
  const std::function<const std::unique_ptr<const std::string>()> & get_value,

libdnf5/conf/vars.cpp

@@ -374,7 +374,7 @@ bool Vars::is_read_only(const std::string & name) const {
 
 void Vars::set(const std::string & name, const std::string & value, Priority prio) {
  if (is_read_only(name)) {
- throw RuntimeError(M_("Variable \"{}\" is read-only"), name);
+ throw ReadOnlyVariableError(M_("Variable \"{}\" is read-only"), name);
  }
 
  // set_unsafe sets the variable without checking whether it's read-only