Exporting C++ code from an R package with Rcpp::interfaces(r, cpp) throws error `PACKAGE_RcppExport_registerCCallable" not available for .Call()`

I'm trying to export C++ functions from my R package 'TreeTools' so they can be called from a different package. I've added the line

// [[Rcpp::interfaces(r, cpp)]]

to src/renumber_tree.cpp, per [https://dirk.eddelbuettel.com/code/rcpp/Rcpp-attributes.pdf / http://r-pkgs.had.co.nz/src.html] and when I compileAttributes() and document() the package, there are indicators that the export has been acknowledged:

Relevant header files are added to inst/includes;
#include "../inst/include/TreeTools.h" is added to the start of RcppExports.cpp
A function RcppExport SEXP _TreeTools_RcppExport_registerCCallable() is added to the end of RcppExports.cpp

Compliation nevertheless fails with

Error in .Call("_TreeTools_RcppExport_registerCCallable", PACKAGE = "TreeTools") : 
  "_TreeTools_RcppExport_registerCCallable" not available for .Call() for package "TreeTools"

Can anyone help me to debug this error? Could it be related to the fact that I have a manually-generated PACKAGE-init.c file?

Solution

Thanks, Dirk, for pointing me in the right direction.

To TreeTools-init.C, I needed to add

extern SEXP _TreeTools_RcppExport_registerCCallable();

and

static const R_CallMethodDef callMethods[] = {
  &_TreeTools_RcppExport_registerCCallable, 0},
  {NULL, NULL, 0}
};

In RcppExports.R, I saw

# Register entry points for exported C++ functions
methods::setLoadAction(function(ns) {
    .Call('_TreeTools_RcppExport_registerCCallable', PACKAGE = 'TreeTools')
})

Replacing the straight quotes around '_TreeTools_RcppExport_registerCCallable' with backticks, i.e.

`_TreeTools_RcppExport_registerCCallable`

allowed the package to load.

Of course, these are replaced with straight quotes whenever compileAttributes() is run, so this doesn't feel like a complete solution...