`linking_to` attribute is no longer supported in `cpp_source()`

[paleolimbot]

This came from a recent build failure for a pkgdown article that uses the cpp11 knitr engine. I don't think I'm using the attribute incorrectly but it's certainly possible!

Reprex from the cpp_source() example page:

cpp11::cpp_source(
  code = '
#include <cpp11/R.hpp>
#include <RProgress.h>

[[cpp11::linking_to("progress")]]

[[cpp11::register]] void
show_progress() {
  RProgress::RProgress pb("Downloading [:bar] ETA: :eta");

  pb.tick(0);
  for (int i = 0; i < 100; i++) {
    usleep(2.0 / 100 * 1000000);
    pb.tick();
  }
}
')
#> Error: cpp11 attributes must be either `cpp11::register` or `cpp11::init`:
#> - Invalid attribute `cpp11::linking_to` on
#> line 5 in file '/var/folders/bq/2rcjstv90nx1_wrt8d3gqw6m0000gn/T//RtmpH9kS6D/file2d7a258fb142/src/code_2d7a7cbe7751.cpp'.

Would it make sense to add linking_to to the list of allowed decorations here?

cpp11/R/register.R

Line 282 in 7a7da57

bad_decor <- !decorations$decoration %in% c("cpp11::register", "cpp11::init")

[paleolimbot]

I think this is also erroring for any C++ signature that contains a regular C++ attribute:

> devtools::load_all(".")
ℹ Loading wk
Error: cpp11 attributes must be either `cpp11::register` or `cpp11::init`:
- Invalid attribute `noreturn` on
line 283 in file '/Users/dewey/Desktop/cran/wk/src/handle-wkt.cpp'.
- Invalid attribute `noreturn` on
line 287 in file '/Users/dewey/Desktop/cran/wk/src/handle-wkt.cpp'.
- Invalid attribute `noreturn` on
line 291 in file '/Users/dewey/Desktop/cran/wk/src/handle-wkt.cpp'.

[jimhester]

@sbearrows we will need to fix the changes in #180 to include cpp11::linking_to (I forgot about it when we discussed it) and to ignore any attribute that doesn't have a cpp11:: prefix.

We should also add some tests to cover the issues that @paleolimbot has kindly reported here.

[sbearrows]

I can start working on this next!

[paleolimbot]

Thank you!