Fuzzer issues (#1202)

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

Author: phlptp

include/CLI/impl/App_inl.hpp

@@ -1670,7 +1670,7 @@ CLI11_INLINE bool App::_parse_single_config(const ConfigItem &item, std::size_t
         throw ConfigError::NotConfigurable(item.fullname());
     }
     if(op->empty()) {
-        std::vector<std::string> buffer;  // a buffer to use for copying an modifying inputs in a few cases
+        std::vector<std::string> buffer;  // a buffer to use for copying and modifying inputs in a few cases
         bool useBuffer{false};
         if(item.multiline) {
             if(!op->get_inject_separator()) {

include/CLI/impl/Config_inl.hpp

@@ -584,8 +584,16 @@ ConfigBase::to_config(const App *app, bool default_also, bool write_description,
                         }
                     }
                 }
-                std::string value =
-                    detail::ini_join(results, arraySeparator, arrayStart, arrayEnd, stringQuote, literalQuote);
+                std::string value;
+                if(opt->count() == 1 && results.size() == 2 && results.front() == "{}" && results.back() == "%%") {
+                    // there is a catch to allow for {} to used as as string in the output
+                    //  it will append a sequence terminator to the output so the lexical conversion handles it
+                    //  correctly but that is meant for config files so when outputting for a config file we need to
+                    //  makes sure to get the correct output
+                    value = "\"{}\"";
+                } else {
+                    value = detail::ini_join(results, arraySeparator, arrayStart, arrayEnd, stringQuote, literalQuote);
+                }
 
                 bool isDefault = false;
                 if(value.empty() && default_also) {

tests/FuzzFailTest.cpp

@@ -345,7 +345,7 @@ TEST_CASE("app_roundtrip_custom") {
     CLI::FuzzApp fuzzdata2;
     auto app = fuzzdata.generateApp();
     auto app2 = fuzzdata2.generateApp();
-    int index = GENERATE(range(1, 24));
+    int index = GENERATE(range(1, 25));
 
     auto parseData = loadFailureFile("round_trip_custom", index);