Make it easier to debugger to do source mapping with cpp11::cpp_source

[renkun-ken]

I have a repo vscode-rcpp-demo to demonstrate how to debug Rcpp C++ code in a package project in VSCode. I also create a similar repo vscode-cpp11-demo to do the same for cpp11. Both work nicely if the project is an R package.

However, in both cases, we cannot debug C++ code with Rcpp::sourceCpp() and cpp11::cpp_source() unless we configure source mapping for the C++ debugger. I raised an issue RcppCore/Rcpp#1041 on Rcpp side, but it seems not trivial to change how the compilation works to support this.

I do some experiment with cpp11, and it seems straightforward to support this: just allow the user to customize https://github.com/r-lib/cpp11/blob/master/R/source.R#L69 so that the directory is pre-determined, and then we can trigger the C++ debugger with the following in a non-package project:

./code.cpp:

#include <cpp11.hpp>
#include <iostream>
using namespace cpp11;

[[cpp11::register]]
double calc_sum(doubles x)
{
  double sum = 0;
  for (int i = 0; i < x.size(); ++i) {
    std::cout << i << std::endl;
    sum += x[i];
  }
  return sum;
}

./code.R:

cpp11::cpp_source("code.cpp", tmpdir = "./tmp")
calc_sum(c(1, 2, 3))

and create a source mapping in .vscode/launch.json:

"sourceFileMap":{
        "${workspaceFolder}/tmp/src/": "${workspaceFolder}/"
      }

Then the breakpoints and other debugger features could work correctly with the source mapping between the original source files and the copied and generated source files in ./tmp/src.

Do you think if it makes sense to allow the user to supply the temp dir for debugging purposes?

[jimhester]

Sure, that seems reasonable, would you be willing to work on a PR to add this?