protect::function compile error with clang

[romainfrancois]

cpp11::cpp_source(code = '
#include <cpp11.hpp>

[[cpp11::register]]
int fun() {
  cpp11::stop("b");
  cpp11::warning("c");
}
', quiet = FALSE)
#> clang++ -mmacosx-version-min=10.13 -std=gnu++11 -I"/Library/Frameworks/R.framework/Resources/include" -DNDEBUG -I/Users/romainfrancois/.R/library/4.0/cpp11/include  -I/usr/local/include   -fPIC  -Wall -O3 -Wall -Wimplicit-int-float-conversion -c /private/var/folders/4b/hn4fq98s6810s4ccv2f9hm2h0000gn/T/RtmpDqea6R/file15b0939b498b1/src/code_0.cpp -o /private/var/folders/4b/hn4fq98s6810s4ccv2f9hm2h0000gn/T/RtmpDqea6R/file15b0939b498b1/src/code_0.o
#> In file included from /private/var/folders/4b/hn4fq98s6810s4ccv2f9hm2h0000gn/T/RtmpDqea6R/file15b0939b498b1/src/code_0.cpp:2:
#> In file included from /Users/romainfrancois/.R/library/4.0/cpp11/include/cpp11.hpp:5:
#> In file included from /Users/romainfrancois/.R/library/4.0/cpp11/include/cpp11/as.hpp:9:
#> /Users/romainfrancois/.R/library/4.0/cpp11/include/cpp11/protect.hpp:236:10: error: definition with same mangled name '_ZNK5cpp117protect8functionIFvPKczEEclIJRS3_EEEDTclsr6detailE5applyclL_ZNSt3__17declvalIPS4_EEDTclsr3std3__1E9__declvalIT_ELi0EEEvEEclsr3stdE16forward_as_tuplespclsr3stdE7forwardIT_Efp_EEEEDpOSD_' as another definition
#>     auto operator()(A&&... a) const
#>          ^
#> /Users/romainfrancois/.R/library/4.0/cpp11/include/cpp11/protect.hpp:236:10: note: previous definition is here
#> 1 error generated.
#> make: *** [/private/var/folders/4b/hn4fq98s6810s4ccv2f9hm2h0000gn/T/RtmpDqea6R/file15b0939b498b1/src/code_0.o] Error 1
#> Error in dyn.load(shared_lib, local = TRUE, now = TRUE): unable to load shared object '/var/folders/4b/hn4fq98s6810s4ccv2f9hm2h0000gn/T//RtmpDqea6R/file15b0939b498b1/src/code_0.so':
#>   dlopen(/var/folders/4b/hn4fq98s6810s4ccv2f9hm2h0000gn/T//RtmpDqea6R/file15b0939b498b1/src/code_0.so, 6): image not found

^{Created on 2020-08-10 by the reprex package (v0.3.0.9001)}

ping @bkietz

This failed to compile array.cpp iin arrow, which looks like:

void arrow::r::validate_slice_length(R_xlen_t length, int64_t available) {
  if (length == NA_INTEGER) {
    cpp11::stop("Slice 'length' cannot be NA");
  }
  if (length < 0) {
    cpp11::stop("Slice 'length' cannot be negative");
  }
  if (length > available) {
    cpp11::warning("Slice 'length' greater than available length");
  }
}

@jimhester can we try to fix this before #84 ?

[jimhester]

I submitted 0.2.0 to CRAN on Friday, but we can do another release in the not too distant future.

[jimhester]

This seems to only be an issue with clang, gcc compiles this without error. Not saying we don't need to fix it, but it seems like a compiler bug perhaps?

[jimhester]

You can workaround the llvm issue using

diff --git a/inst/include/cpp11/protect.hpp b/inst/include/cpp11/protect.hpp
index fe5f8aa..bcb6781 100644
--- a/inst/include/cpp11/protect.hpp
+++ b/inst/include/cpp11/protect.hpp
@@ -271,12 +271,12 @@ void stop [[noreturn]] (const std::string& fmt, Args... args) {

 template <typename... Args>
 void warning(const char* fmt, Args... args) {
-  safe[Rf_warning](fmt, args...);
+  unwind_protect([&] { Rf_warning(fmt, args...); });
 }

 template <typename... Args>
 void warning(const std::string& fmt, Args... args) {
-  safe[Rf_warning](fmt.c_str(), args...);
+  unwind_protect([&] { Rf_warning(fmt.c_str(), args...); });
 }

 }  // namespace cpp11

But that then doesn't work with gcc 4.8.5

[romainfrancois]

That's fine, if anything we can vendor cpp11 if we need to release it. I'll let @bkietz come up with a compiler conditional compilation strategy as this seems to be a mix of too many things I'm not that confortable with (constexpr, tuples, declval, ...)

[bkietz]

The root of the problem is that Rf_error and Rf_warning don't have identical type because Rf_error carries [[noreturn]] but the two types do mangle identically

<stdin>:35:3: error: static_assert failed due to requirement 'std::is_same<void (const char *, ...) __attribute__((noreturn)), void (const char *, ...)>::value' ""
  static_assert(std::is_same<decltype(Rf_error), decltype(Rf_warning)>::value, "");
  ^             ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

[nealrichardson]

I don't fully understand why this is a problem now and not before but we can also work around this in arrow by removing the warning.

[jimhester]

Even if you can work around the particular issue in arrow being able to have a cpp11::stop() and a cpp11::warning() in the same compilation unit seems something we need to support.

Does removing the [[noreturn]] annotation fix this issue then?

[romainfrancois]

And/or can we embed the no-return-ness in the type somehow ?

[bkietz]

fixes the issue for me: 25014d8

[bkietz]

Does removing the [[noreturn]] annotation fix this issue then?

Yes, but I don't think that will be necessary.

And/or can we embed the no-return-ness in the type somehow ?

I tried that, but clang and gcc don't handle attributes consistently enough to write enable_if_noreturn (or at least I couldn't swing it).

[bkietz]

resolved by #85