Found this on LLVM Weekly. Neat project.

Unfortunately, lambda handling seems quite buggy. For example:

void x()
{
  auto a = [](){
    [](){};
  };
}

void x()
{

   class __lambda_3
   {
     public: inline /*constexpr */ void operator()() const
     {
       __lambda_4;
     }
     
   };
   
   
   class __lambda_4
   {
     public: inline /*constexpr */ void operator()() const
     {
     }
     
   };
   
     __lambda_3 a = __lambda_4{}da_3{};
}

I'm not sure what __lambda_3; in operator() is supposed to do, and __lambda_4{}da_3{} is nonsense.

I suspect you're replacing the substring at [4,7) with something longer, then doing another replacement on the same line, without adjusting the offsets to account for the previous replacement. This yields lots of strange output (another example: removing auto a = makes it emit lambdas in the output), but I think most or all of it is all the same root cause.

(Additionally, two lambdas on the same line expand to two classes with the same name. Append column number to subsequent ones, maybe?)