Replace single char strings with char literals

Author: lucic71

cpp2rust/converter/models/converter_refcount.cpp

@@ -196,7 +196,7 @@ std::string ConverterRefCount::BuildFnAdapter(
   closure += "{ ";
 
   // Build adapter body: src_fn(convert(a0), convert(a1), ...)
-  closure += Mapper::MapFunctionName(src_fn) + "(";
+  closure += Mapper::MapFunctionName(src_fn) + '(';
   for (unsigned i = 0; i < src_proto->getNumParams(); ++i) {
     auto src_pty = src_proto->getParamType(i);
     auto tgt_pty = target_proto->getParamType(i);

cpp2rust/converter/translation_rule.cpp

@@ -495,7 +495,7 @@ std::vector<Rule> Load(const std::filesystem::path &path, Model model) {
   for (auto &[name, rule] : rules) {
     assert(!rule.src.empty() && "Rule loaded from IR but has no src");
     if (auto *expr_tgt = std::get_if<ExprTgt>(&rule.tgt)) {
-      expr_tgt->validate(path.string() + ":" + name);
+      expr_tgt->validate(path.string() + ':' + name);
     }
     result.push_back(std::move(rule));
   }