Bug 207757 – [GStreamer] Build failure with Clang/libc++ due to missing WallTime→float for std::isnan()

• Component: Tools / Tests
• Status: RESOLVED FIXED

[Adrian Perez]

WPE WebKit 2.27.90 (and most surely the GTK port as well) fail to build with
Clang when using libc++ (instead of GNU stdlibc++).

Configuration command:

  CC=clang CXX=clang++ \
  LDFLAGS='-stdlib=libc++ -fuse-ld=lld' \
  CXXLAGS='-stdlib=libc++' \
  cmake -DPORT=WPE -DUSE_LD_GOLD=OFF -DUSE_LD_LLD=ON <...>

Build error:

  ../Source/WebCore/platform/graphics/gstreamer/WebKitWebSourceGStreamer.cpp:1155:10: error: no matching function for call to 'isnan'
      if (!isnan(priv->downloadStartTime)) {
           ^~~~~
  /usr/bin/../include/c++/v1/math.h:535:1: note: candidate function not viable: no known conversion from 'WTF::WallTime' to 'float' for 1st argument
  isnan(float __lcpp_x) _NOEXCEPT { return __libcpp_isnan(__lcpp_x); }
  ^
  /usr/bin/../include/c++/v1/math.h:539:1: note: candidate function not viable: no known conversion from 'WTF::WallTime' to 'double' for 1st argument
  isnan(double __lcpp_x) _NOEXCEPT { return __libcpp_isnan(__lcpp_x); }
  ^
  /usr/bin/../include/c++/v1/math.h:543:1: note: candidate function not viable: no known conversion from 'WTF::WallTime' to 'long double' for 1st argument
  isnan(long double __lcpp_x) _NOEXCEPT { return __libcpp_isnan(__lcpp_x); }
  ^
  /usr/bin/../include/c++/v1/math.h:521:1: note: candidate template ignored: requirement 'std::is_floating_point<WTF::WallTime>::value' was not satisfied [with _A1 = WTF::WallTime]
  isnan(_A1 __lcpp_x) _NOEXCEPT
  ^
  /usr/bin/../include/c++/v1/math.h:529:1: note: candidate template ignored: requirement 'std::is_integral<WTF::WallTime>::value' was not satisfied [with _A1 = WTF::WallTime]
  isnan(_A1) _NOEXCEPT
  ^
  1 error generated.

[Adrian Perez]

This happens in trunk as well. There are “std::isnan()” overloads
defined for “WTF::Walltime”, but Clang is being a bit more strict
than GCC here and not considering them when using a bare “isnan()“
call (without the namespace) because the overloaded version is
inside the namespace, and there us no “using std::isnan;” (or
equivalent) anywhere when non-unified builds are disabled.

The fix is to add the “std::” namespace prefix to the function
call =)

[Adrian Perez]

Created attachment 390864 [details]
Patch

[Adrian Perez]

Comment on attachment 390864 [details]
Patch

Clearing flags on attachment: 390864

Committed r256706: <https://trac.webkit.org/changeset/256706>

[Adrian Perez]

All reviewed patches have been landed.  Closing bug.

[Radar WebKit Bug Importer]

<rdar://problem/59488736>