Rcpp: Setting parenthesis characters as default value to function parameters yields a compiling error

[pkrog]

Defining the following function:

Rcpp::sourceCpp(code = '//[[Rcpp::export]]
void foo(const char* a = "(", const char* b= ")") {}')

gives:

file8586f8153c2.cpp: In function ‘SEXPREC* sourceCpp_63_foo(SEXP)’:
file8586f8153c2.cpp:12:10: error: call of overloaded ‘foo(Rcpp::traits::input_parameter<const char*>::type&)’ is ambiguous
   12 |     foo(a);
      |          ^
file8586f8153c2.cpp:2:6: note: candidate: ‘void foo(const char*, const char*)’
    2 | void foo(const char* a = "(", const char* b= ")") {}
      |      ^~~
file8586f8153c2.cpp:7:6: note: candidate: ‘void foo(const char*)’
    7 | void foo(const char* a);
      |      ^~~
make: *** [/usr/lib64/R/etc/Makeconf:176: file8586f8153c2.o] Error 1
g++ -std=gnu++11 -I"/usr/include/R/" -DNDEBUG   -I"/home/pr228844/R/x86_64-pc-linux-gnu-library/3.6/Rcpp/include" -I"/tmp/RtmpTogNDM/sourceCpp-x86_64-pc-linux-gnu-1.0.1" -D_FORTIFY_SOURCE=2  -fpic  -march=x86-64 -mtune=generic -O2 -pipe -fstack-protector-strong -fno-plt  -c file8586f8153c2.cpp -o file8586f8153c2.o
Error in Rcpp::sourceCpp(code = "//[[Rcpp::export]]\nvoid foo(const char* a = \"(\", const char* b= \")\") {}") : 
  Error 1 occurred building shared library.

Inverting the default values, leads to the same error:

Rcpp::sourceCpp(code = '//[[Rcpp::export]]
void foo(const char* a = ")", const char* b= "(") {}')

Replacing one of the default values with another value, remove the error:

Rcpp::sourceCpp(code = '//[[Rcpp::export]]
void foo(const char* a = "x", const char* b= "(") {}')

[kevinushey]

I think this is a bug in the hand-rolled C++ parser used for attributes. Since this is somewhat of an edge case, it's unlikely we'll fix this quickly -- but pull requests are welcome!

[eddelbuettel]

Seconded. I glanced iinto src/attributes.cpp but didn't find the regexp immediately. Sounds entirely fixable with a bit of patience so contributions welcome...

[jjallaire]

There's no regex, it's just a lookahead tokenizer. We have some logic to
exclude e.g. commas within quotes but I don't know if this can be easily
extended to parentheses. Would indeed be happy to review a PR.

On Tue, Jul 9, 2019 at 5:01 PM Dirk Eddelbuettel [e-mail]
wrote:

Seconded. I glanced iinto src/attributes.cpp but didn't find the regexp
immediately. Sounds entirely fixable with a bit of patience so
contributions welcome...

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[pkrog]

I've made the corrections and am going to make a pull request.

[eddelbuettel]

Thanks for the PR and the tests!