Clang Modules与std <iterator>和<boost/move/iterator.hpp>的交互

Question

(有关我正在使用的特定版本的Boost和Clang的信息,请参阅问题的结尾)

使用新的实验性-fmodules功能在master/HEAD中编译Clang,使用下面显示的命令行选项编译以下文件时出现构建错误:

#include <iterator>
#include <boost/move/iterator.hpp>

编译命令和错误:

anhall@leviathan: <path-to-clang-install-from-master>/bin/clang++ -o file.o -c file.cpp --std=c++1z -stdlib=libc++ -fmodules

In file included from file.cpp:2:
In file included from /usr/local/include/boost/move/iterator.hpp:27:
/usr/local/include/boost/move/detail/iterator_traits.hpp:60:17: error: reference to 'random_access_iterator_tag' is ambiguous
   typedef std::random_access_iterator_tag   iterator_category;
                ^
/Users/anhall/impersonal/code/llvm-reflexpr/install/bin/../include/c++/v1/iterator:438:30: note: candidate found by name lookup is 'std::__1::random_access_iterator_tag'
struct _LIBCPP_TYPE_VIS_ONLY random_access_iterator_tag : public bidirectional_iterator_tag {};
                             ^
/usr/local/include/boost/move/detail/iterator_traits.hpp:34:8: note: candidate found by name lookup is 'std::random_access_iterator_tag'
struct random_access_iterator_tag;
       ^
/usr/local/include/boost/move/detail/iterator_traits.hpp:71:17: error: reference to 'random_access_iterator_tag' is ambiguous
   typedef std::random_access_iterator_tag   iterator_category;
                ^
/Users/anhall/impersonal/code/llvm-reflexpr/install/bin/../include/c++/v1/iterator:438:30: note: candidate found by name lookup is 'std::__1::random_access_iterator_tag'
struct _LIBCPP_TYPE_VIS_ONLY random_access_iterator_tag : public bidirectional_iterator_tag {};
                             ^
/usr/local/include/boost/move/detail/iterator_traits.hpp:34:8: note: candidate found by name lookup is 'std::random_access_iterator_tag'
struct random_access_iterator_tag;
       ^
In file included from file.cpp:2:
/usr/local/include/boost/move/iterator.hpp:196:17: error: reference to 'output_iterator_tag' is ambiguous
   typedef std::output_iterator_tag    iterator_category;
                ^
/Users/anhall/impersonal/code/llvm-reflexpr/install/bin/../include/c++/v1/iterator:435:30: note: candidate found by name lookup is 'std::__1::output_iterator_tag'
struct _LIBCPP_TYPE_VIS_ONLY output_iterator_tag {};
                             ^
/usr/local/include/boost/move/detail/iterator_traits.hpp:35:8: note: candidate found by name lookup is 'std::output_iterator_tag'
struct output_iterator_tag;
       ^
In file included from file.cpp:2:
/usr/local/include/boost/move/iterator.hpp:238:17: error: reference to 'output_iterator_tag' is ambiguous
   typedef std::output_iterator_tag    iterator_category;
                ^
/Users/anhall/impersonal/code/llvm-reflexpr/install/bin/../include/c++/v1/iterator:435:30: note: candidate found by name lookup is 'std::__1::output_iterator_tag'
struct _LIBCPP_TYPE_VIS_ONLY output_iterator_tag {};
                             ^
/usr/local/include/boost/move/detail/iterator_traits.hpp:35:8: note: candidate found by name lookup is 'std::output_iterator_tag'
struct output_iterator_tag;
       ^
In file included from file.cpp:2:
/usr/local/include/boost/move/iterator.hpp:278:17: error: reference to 'output_iterator_tag' is ambiguous
   typedef std::output_iterator_tag    iterator_category;
                ^
/Users/anhall/impersonal/code/llvm-reflexpr/install/bin/../include/c++/v1/iterator:435:30: note: candidate found by name lookup is 'std::__1::output_iterator_tag'
struct _LIBCPP_TYPE_VIS_ONLY output_iterator_tag {};
                             ^
/usr/local/include/boost/move/detail/iterator_traits.hpp:35:8: note: candidate found by name lookup is 'std::output_iterator_tag'
struct output_iterator_tag;
       ^
5 errors generated.

如果我删除#include <iterator>或移动后#include <boost/move/iterator.hpp>,错误消失.

问题:这只是Boost库的副产品(Boost Move,特别是,显然)没有为具有Clang模块映射文件的模块做好准备吗？这可能是Clang现在为libc ++实现的模块映射文件的错误,甚至模块实现本身的错误？

有趣的是,我可以通过评论第28-28行来消除错误boost/move/detail/iterator_traits.hpp:

// #include <boost/move/detail/std_ns_begin.hpp>
// BOOST_MOVE_STD_NS_BEG
//
// struct input_iterator_tag;
// struct forward_iterator_tag;
// struct bidirectional_iterator_tag;
// struct random_access_iterator_tag;
// struct output_iterator_tag;
//
// BOOST_MOVE_STD_NS_END
// #include <boost/move/detail/std_ns_end.hpp>

正在使用的版本

提升1.61

截至2016年12月7日,Clang来自LLVM的github镜像中的主分支的尖端(技术上它来自LLVM的分支,但它只在主分支上与LLVM自己的主分支相同):

clang version 4.0.0 (https://github.com/matus-chochlik/clang.git b9cb1c8a1ebf52695372de12c7b04c8ef1bd8b4e) (https://github.com/llvm-mirror/llvm.git b60c7b1f61eabbe971d08568adb790a7cfc6a403)
Target: x86_64-apple-darwin15.6.0
Thread model: posix
InstalledDir: /Users/anhall/impersonal/code/llvm-reflexpr/install/bin

Answer 1

我相信这是由 libc++ 的 module.modulemap 问题引起的，我昨天在r289028中修复了该问题。此错误导致_LIBCPP_VERSION启用模块时 libc++ 无法导出宏。

经过查看后boost/move/detail/iterator_traits.hpp发现，如果_LIBCPP_VERSION未定义，它将错过配置并最终声明迭代器标签的完全不同的定义。（具体来说，它将直接在命名空间中定义它们std，而不是在 libc++ 的版本控制命名空间中）。

如果您重新构建 LLVM 和 libc++ 它应该可以解决您的问题。如果没有，请随时提交错误。

附言。看来我只领先一步了。