OS X compile error: call to 'abs' is ambiguous

[springmeyer]

This is happening on Travis's OS X machines. Full log is here. Details on XCode for this machine is here.

One odd thing is that c++11 should not be enabled and libc++ should not be being linked because -DOSXLIBSTD="libstdc++" is being passed to cmake, but the configure output says:

-- Activating -std=c++11 flag for >= OS X 10.9
-- linking against libc++

Error is:

[ 22%] Building CXX object CMakeFiles/OSRM.dir/Algorithms/DouglasPeucker.cpp.o
/Users/travis/build/DennisOSRM/node-osrm/Project-OSRM/Algorithms/DouglasPeucker.cpp:102:37: error: 
      call to 'abs' is ambiguous
            const double distance = std::abs(temp_dist);
                                    ^~~~~~~~
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../lib/c++/v1/cmath:660:1: note: 
      candidate function
abs(float __x) _NOEXCEPT {return fabsf(__x);}
^
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../lib/c++/v1/cmath:664:1: note: 
      candidate function
abs(double __x) _NOEXCEPT {return fabs(__x);}
^
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../lib/c++/v1/cmath:668:1: note: 
      candidate function
abs(long double __x) _NOEXCEPT {return fabsl(__x);}
^
1 error generated.
make[2]: *** [CMakeFiles/OSRM.dir/Algorithms/DouglasPeucker.cpp.o] Error 1

[springmeyer]

turns out this problem is occuring when building OSRM against homebrew installed deps:

brew install boost cmake protobuf libstxxl lua luabind osm-pbf

As such this is not a problem for me, since my primary approach is to build against static deps.

[DennisOSRM]

@springmeyer thx for the feedback.

[springmeyer]

was able to replicate. Going to keep closed until this is actionable, but log some notes here as I find details about what is going on....

[springmeyer]

This works around the problem:

+ const double distance = std::abs((double)temp_dist);
- const double distance = std::abs(temp_dist);

[springmeyer]

re-opening, this looks to me like a libc++/c++11 bug, but will need a workaround in OSRM.

Here is a reduced testcase:

#include <cmath>
/*
Workaround by including this header:
#include <cstdlib>
Or workaround by doing:
    const double distance = std::abs((double)temp_dist);
Or by doing:
    const double distance = std::fabs(temp_dist);
*/

/*
clang++ -o abs abs.cpp
abs.cpp:17:29: error: call to 'abs' is ambiguous
    const double distance = std::abs(temp_dist);
                            ^~~~~~~~
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../lib/c++/v1/cmath:660:1: note: candidate function
abs(float __x) _NOEXCEPT {return fabsf(__x);}
^
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../lib/c++/v1/cmath:664:1: note: candidate function
abs(double __x) _NOEXCEPT {return fabs(__x);}
^
/Applications/Xcode.app/Contents/Developer/Toolchains/XcodeDefault.xctoolchain/usr/bin/../lib/c++/v1/cmath:668:1: note: candidate function
abs(long double __x) _NOEXCEPT {return fabsl(__x);}
^
1 error generated.


$ clang++ -v
Apple LLVM version 5.1 (clang-503.0.40) (based on LLVM 3.4svn)
Target: x86_64-apple-darwin13.1.0
Thread model: posix

*/

int main() {
    const int temp_dist = -1;
    const double distance = std::fabs(temp_dist);
    return 0;
}

[springmeyer]

I'll summarize:

• This occurs with latest clang++ on OS X and is easy to replicate when building OSRM against libc++ in c++11 mode
• There are numerous possible workarounds. I think the simplest is to use std::fabs

[DennisOSRM]

Thx. I'll Look into it.

[DennisOSRM]

Working on a fix

[DennisOSRM]

Fix will be pushed in a couple of minutes once tests have passed locally. The reason was simple and somewhat dull. The variable temp_dist should not have been int after all but a double.

[DennisOSRM]

@springmeyer is this still an issue?

[springmeyer]

yes

[DennisOSRM]

yes=no? ;-)

[springmeyer]

haha, sorry, yes this is fixed. no it is not still an issue :)

[DennisOSRM]

Cool. Thx

[entangledloops]

Headsup: the fabs solution works for clang, but doesn't work with at least Visual Studio 2013 (which will now report ambiguous call for fabs).