Allow only safe types to be passed to libdnf5::Error and SystemError …

…ctors

Exceptions were generated in the code, in which a pointer to text was
passed that was no longer in memory at the time the exception was handled.

To prevent this from happening again, passing only defined "safe" types
is now allowed.

include/libdnf5/common/exception.hpp

@@ -27,6 +27,7 @@ along with libdnf.  If not, see <https://www.gnu.org/licenses/>.
 
 #include <functional>
 #include <stdexcept>
+#include <type_traits>
 
 #define LIBDNF_LOCATION \
     { __FILE__, __LINE__, __PRETTY_FUNCTION__ }
@@ -122,6 +123,20 @@ class UserAssertionError : public std::logic_error {
 };
 
 
+// The exception stores the passed arguments and uses them in the catch phase.
+// The problem is that the value to which the saved argument points may no longer be in memory -
+// is destroyed when the program leaves the scope of the variable with the value.
+// A safer solution than passing a pointer to memory is to use "std::string" and pass it by value.
+//
+// "Concept" defines safe types that can be passed by value as arguments to the "libdnf5::Error"
+// and "libdnf5::SystemError" exception constructors.
+// Pointers to void are allowed because they are not dereferenced, but their value is printed.
+template <typename T>
+concept AllowedErrorArgTypes =
+    std::is_arithmetic_v<T> || std::is_base_of_v<std::string, T> || std::is_null_pointer_v<T> ||
+    std::is_same_v<const void *, T> || std::is_same_v<void *, T>;
+
+
 /// Base class for libdnf exceptions. Virtual methods `get_name()` and
 /// `get_domain_name()` should always return the exception's class name and its
 /// namespace (including enclosing class names in case the exception is nested in
@@ -132,7 +147,7 @@ class Error : public std::runtime_error {
     ///
     /// @param format The format string for the message.
     /// @param args The format arguments.
-    template <typename... Args>
+    template <AllowedErrorArgTypes... Args>
     explicit Error(BgettextMessage format, Args... args)
         : std::runtime_error(b_gettextmsg_get_id(format)),
           format(format),
@@ -172,7 +187,7 @@ class SystemError : public Error {
     /// @param error_code The `errno` of the error.
     /// @param format The format string for the message.
     /// @param args The format arguments.
-    template <typename... Args>
+    template <AllowedErrorArgTypes... Args>
     explicit SystemError(int error_code, BgettextMessage format, Args... args)
         : Error(format, std::forward<Args>(args)...),
           error_code(error_code),