c++ - Clang 模块与 std 和 交互

Question

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

使用新的实验性 -fmodules 从 master/HEAD 在 Clang 中编译功能，使用如下所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>

编译命令及错误:

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>或将其移到 #include <boost/move/iterator.hpp> 之后，错误消失。

问题:这是否只是 Boost 库(显然尤其是 Boost Move)没有为具有 Clang 模块映射文件的模块准备的副产品？这可能是 Clang 现在为 libc++ 实现的模块映射文件的错误，甚至是模块实现本身的错误？

有趣的是，我可以通过注释掉 boost/move/detail/iterator_traits.hpp 的第 28-28 行来消除错误。 :

// #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

boost 1.61

截至 2016 年 12 月 7 日，Clang 来自 LLVM github 镜像中 master 分支的尖端(技术上它来自 LLVM 的一个分支，但它仅在与 LLVM 自己的 master 分支相同的 master 分支上):

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 宏在启用模块时无法由 libc++ 导出。

在查看了 boost/move/detail/iterator_traits.hpp 之后，似乎如果 _LIBCPP_VERSION 没有被定义，它将配置错误并最终声明完全不同的定义迭代器标签。 (具体来说，它将直接在命名空间 std 中定义它们，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++，它应该解决您的问题。如有不便file a bug .

附言。看来我只是one step ahead .