[MacPorts] #54820: missing std::trunc and other std:: math functions when building webkit2-gtk on 10.6 using macports-libsdtc++ and libgcc headers

[MacPorts]

#54820: missing std::trunc and other std:: math functions when building webkit2-gtk
on 10.6 using macports-libsdtc++ and libgcc headers
-------------------------+-------------------------
 Reporter:  kencu        |      Owner:
     Type:  defect       |     Status:  new
 Priority:  Normal       |  Milestone:
Component:  ports        |    Version:
 Keywords:  snowleopard  |       Port:  webkit2-gtk
-------------------------+-------------------------
 Sorry for the long title -- try to be precise. I recently fixed
 `webkit2-gtk` to build on older systems, but it failed on the buildbot on
 the setup described above, which I believe may have uncovered a `cmath`
 flaw on that system.  `10.6/libc++` worked fine, `10.6/macports-libstdc++`
 did not.

 Initially the error was a single missing definition for `std::trunc` but
 when I edited that in the source file to `trunc()` a number of other
 `std:: math` functions came up missing so it was a more general issue. I
 then tried building with `gcc6` instead `clang-4.0`, but same exact error
 in the same file (full log enclosed, clang-4.0 error was essentially
 identical).

 Looking through the math headers, the missing function was indeed
 available in `/opt/local/include/gcc6/c++/cmath`, but guarded by this:
 {{{
 #ifdef _GLIBCXX_USE_C99_MATH_TR1
 }}}
 Adding that definition like so
 {{{add_definitions(-D_GLIBCXX_USE_C99_MATH_TR1)}}} to the CMakeLists.txt
 file quickly ran into errors for missing definitions for {{{llrint}}} and
 similar long long definitions. This is exactly the same issue Jeremy had
 to fix in the libc++ math headers on 10.6, I recalled.

 I took the same block from Jeremy's clang/libc++ fix, and pasted it into
 {{{/opt/local/include/gcc6/c++/cmath}}} like so:
 {{{
 ....

 #ifndef _GLIBCXX_CMATH
 #define _GLIBCXX_CMATH 1

 +# if __has_include(<Availability.h>)
 +#  include <Availability.h>
 +#  if __MAC_OS_X_VERSION_MAX_ALLOWED < 1070
 +#    define __APPLE_BAD_MATH_H 1
 +#  else
 +#    define __APPLE_BAD_MATH_H 0
 +#  endif
 +# else
 +#  define __APPLE_BAD_MATH_H 1
 +# endif
 +
 +# if __APPLE_BAD_MATH_H
 +/* These prototypes are incorrectly omitted from <math.h> on Snow Leopard
 despite being available */
 +extern "C" {
 +    extern long long int llrintl(long double);
 +    extern long long int llrint(double);
 +    extern long long int llrintf(float);
 +
 +    extern long long int llroundl(long double);
 +    extern long long int llround(double);
 +    extern long long int llroundf(float);
 +}
 +# endif
 +#endif // __APPLE__

 // Get rid of those macros defined in <math.h> in lieu of real functions.
 #undef abs
 #undef div

 ....
 }}}

 and then webkit2-gtk proceeded to build through to completion.

 1. I'm not fully clear why 10.6 would need
 {{{-D_GLIBCXX_USE_C99_MATH_TR1}}} defined and not the others similarly
 building with gcc6's cmath. I can't seem to find any test or reference for
 this in the {{{webkit2-gtk}}} configure logic.
 2. it appears 10.6 and lower will probably need Jeremy's fix as above in
 {{{/opt/local/include/gcc6/c++/cmath}}}

 These are easy enough to add, if this is indeed the right thing to do, in
 the end.

--
Ticket URL: <https://trac.macports.org/ticket/54820>
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