cpp_source fails to compile indented void-returning function

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Assessment

Difficulty
3/5
Estimated time
1-2 days
Newbie friendliness
42/100
Issue type
Bug
Clarity
Mostly clear
Activity status
Stale
Tech stack
cpp, r
Domain
tooling

Research direction

Start by reproducing the failure with cpp11::cpp_source using the inline snippets, then compare it with the equivalent external-file case. Trace how cpp11 identifies the void return type and generates the wrapper, focusing on the leading space before the function declaration. Done means indented void-returning functions compile successfully in both inline and external-source cases.

Written by the indexing model from the issue text.

Description

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’
Dominant language
C++
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