Rcpp: No Rcpp::export attributes when www links (among others) appear in /**/-style comments

[gagolews]

Compilation of the following source file:

#include <Rcpp.h>
using namespace Rcpp;

/* this is a bug: http://bugbugbug.com  */

// [[Rcpp::export]]
NumericVector timesTwo(NumericVector x) {
  return x * 2;
}

Ends up with the following warning:

Warning message:
In Rcpp::sourceCpp("/tmp/test.cpp") :
  No Rcpp::export attributes or RCPP_MODULE declarations found in source

Thanks for making R-C++ integration really seamless!

[gagolews]

I guess a minimal reproducible buggy-comment is:

/* //  */

[eddelbuettel]

What happens when you use

// this is a bug: http://bugbugbug.com  

[gagolews]

This only affects /**/ - style comments.

[eddelbuettel]

"Doctor, doctor, it hurts when I do this."
"Then don't do it."

We'll leave this open to remind us to make the regexp parser smarter. In the meantime, maybe stick to // comments when URLs with double forward slashes are embedded.

[gagolews]

Jolly good.

[eddelbuettel]

It's a valid bug report, of course, but luckily not too many people have been bitten.

[gagolews]

On a side note, I always wondered why

/* [[Rcpp::export]] */

is not a synonym for

// [[Rcpp::export]]

[eddelbuettel]

Maybe because the project is called Rcpp and not Rc ? ;-)

The parser in src/attributes is open source like the rest of it. If you have an itch to scratch, and can do it in a way that does not create side effects or regressions we might very well include it...

[coatless]

I haven't dug into this yet. But, I'm assuming that something is off with the regex specified src/attributes.cpp#L1141-L1142:

Or one of the other regex matches is picking it up....

"^\\s*//\\s*\\[\\[Rcpp::(\\w+)(\\(.*?\\))?\\]\\]\\s*$"

[eddelbuettel]

There may be dragons. Most of this is by @jjallaire , I would heed his sage advice as to what to try and not. Over the years we added a special treatment for a forgotten corner case here or there.

This one does not strike me as terribly important. It is a bug, yes. It should get fixed, yes.

But a million other things also compete for attention and this is, quite frankly, not that high up on my list.

[jjallaire]

I agree. I smudge but not one we should set aside the time to wipe away right now.

[coatless]

In the interim, add it to the known issues section per @thirdwing ?

[thirdwing]

BTW, it seems this issue has already been reported in #161

[david-cortes]

Tip: this can be fixed by adding a further comment with /* */ below, e.g.

#include <Rcpp.h>
using namespace Rcpp;

/*  This will introduce a problem
    https://github.com/RcppCore/Rcpp/issues/978 */
/* this fixes it */
// [[Rcpp::export]]
List rcpp_hello_world() {

    CharacterVector x = CharacterVector::create( "foo", "bar" )  ;
    NumericVector y   = NumericVector::create( 0.0, 1.0 ) ;
    List z            = List::create( x, y ) ;

    return z ;
}

[github-actions[bot]]

This issue is stale (365 days without activity) and will be closed in 31 days unless new activity is seen. Please feel free to re-open it is still a concern, possibly with additional data.