cpp_source fails to compile indented void-returning function

[plietar]

trafficstars

If a void-returning function marked with cpp11::register is indented, cpp11 fails to recognize the void return type and will try to use its result in the wrapper it generates.

# This works
cpp11::cpp_source(code = "[[cpp11::register]]\nvoid foo() {}")

# This fails to compile. Note the extra space character between the newline and void
cpp11::cpp_source(code = "[[cpp11::register]]\n void foo() {}")

using C++ compiler: ‘g++ (GCC) 14.2.1 20241116’
using C++11
/tmp/nix-shell.Cz8fPO/RtmpadKzBh/code_16bff7617b36f0.cpp:2:11: warning: ‘cpp11::register’ scoped attribute directive ignored [-Wattributes]
    2 |  void foo() {}
      |           ^
/tmp/nix-shell.Cz8fPO/RtmpadKzBh/file16bff7121f1a99/src/cpp11.cpp: In function ‘SEXPREC* _code_16bff7617b36f0_foo()’:
/tmp/nix-shell.Cz8fPO/RtmpadKzBh/file16bff7121f1a99/src/cpp11.cpp:7:30: error: invalid use of void expression
    7 |     return cpp11::as_sexp(foo());
      |                           ~~~^~
make: *** [/nix/store/bb3gfb6b740ha50bbwvbgslybnqm0vgf-R-4.4.3/lib/R/etc/Makeconf:204: /tmp/nix-shell.Cz8fPO/RtmpadKzBh/file16bff7121f1a99/src/cpp11.o] Error 1
Error: Compilation failed.

The same behaviour happens when using an external file instead of an inline code = argument.

packageVersion("cpp11")
#> [1] ‘0.5.2’

[pachadotdev]

hi @plietar I use cpp11 in my lab I proposed a fix to decor such that signature becomes "void foo()" (not " void foo()"), and the C parser shall see the void return type and generate the correct (void‐returning) wrapper https://github.com/r-lib/decor/compare/main...pachadotdev:decor:patch-1