${antlr4cpp_src_files_antlrcpptest} is empty on build

[gress2]

Hello,

Because of some subtleties of CMake, it looks like this variable is actually not set when

add_executable(test_antlr main.cpp ${antlr4cpp_src_files_antlrcpptest}) is called. I think this is due to the fact that this variable is set at build time.

As a result, the linker will not be able to resolve references to TParser, etc. This can be seen with the following main.cpp:

#include <iostream>
#include <antlr4-runtime.h>
#include "TParser.h"

int main() {
  std::cout << "Hello World" << std::endl;
  antlrcpptest::TParser tp(nullptr);
  return 0;
}

CMakeFiles/test_antlr.dir/main.cpp.o: In function `main':
main.cpp:(.text+0x53): undefined reference to `antlrcpptest::TParser::TParser(antlr4::TokenStream*)'
main.cpp:(.text+0x67): undefined reference to `antlrcpptest::TParser::~TParser()'

This seems to only be the case on a fresh build i.e. one where cmake .. has only been done once. The next time cmake is run this variable will be populated, and the build will succeed.