[MSVC] Disable <fstream> usage of <filesystem>

[rnk]

Summary

ninja cxx now succeeds for me locally.

This fixes link errors when producing a DLL for libc++ with clang-cl.
When building a DLL, most of <filesystem> is annotated as dllexport.
When a class is marked dllexport, all of its inline functions are
emitted into the object file. Those inline functions reference
out-of-line functions that are not available because the filesystem cpp
files are not built on Windows because they haven't been ported yet.

[mstorsjo]

libcxx/include/fstream

190

I'm not entirely fond of hardcoding the condition like this - would it be better to emit something to __config (via __config_site) about whether filesystem is disabled?

I guess hardcoding msvc could be argued for, because the dllexport behaviour is kinda msvc specific (this problem doesn't manifest in mingw builds, that build successfully in dll mode).

Another reason for not hardcoding it for msvc, is that while filesystem is disabled for now, it hopefully won't be for long, and it'd be nice not to have an extra condition to keep track of to update in sync.

[rnk]

libcxx/include/fstream

190

I think if the project wants to support the LIBCXX_ENABLE_FILESYSTEM option over the long run, then it probably makes sense to feed that into __config_site and use that to control this include and the availability of these overloads.

However, if we view this as a temporary portability work around, then I think it makes sense to limit the scope of the workaround as much as possible.

[mstorsjo]

libcxx/include/fstream

190

Fair enough. Wrt enabling filesystem in msvc configurations, the int128 builtin issue (see D91139) remains. (For mingw configurations, the patchset in review is everything that is needed.)

[ldionne]

@rnk Can you please take a look at https://reviews.llvm.org/D94921 and tell me if that solves your issues? That would be my preferred way forward.

[rnk]

In D94824#2505131, @ldionne wrote:

@rnk Can you please take a look at https://reviews.llvm.org/D94921 and tell me if that solves your issues? That would be my preferred way forward.

Yep, that should work for us. I haven't patched in and tested yet, but I'll send follow up patches if it doesn't work on the first try.

libcxx/include/fstream

 
 #include <__config>
 #include <__availability>
 #include <ostream>
 #include <istream>
 #include <__locale>
 #include <cstdio>
 #include <cstdlib>
+
+#if _LIBCPP_STD_VER >= 17 && !defined(_MSC_VER)
 #include <filesystem>
+#define _LIBCPP_ENABLE_FILESYSTEM_OVERLOADS
+#endif
 
 #if !defined(_LIBCPP_HAS_NO_PRAGMA_SYSTEM_HEADER)
 #pragma GCC system_header
 #endif
 
 _LIBCPP_PUSH_MACROS
 #include <__undef_macros>
 

 #ifndef _LIBCPP_HAS_NO_GLOBAL_FILESYSTEM_NAMESPACE
     basic_filebuf* open(const char* __s, ios_base::openmode __mode);
 #ifdef _LIBCPP_HAS_OPEN_WITH_WCHAR
     basic_filebuf* open(const wchar_t* __s, ios_base::openmode __mode);
 #endif
     _LIBCPP_INLINE_VISIBILITY
     basic_filebuf* open(const string& __s, ios_base::openmode __mode);
 
-#if _LIBCPP_STD_VER >= 17
+#ifdef _LIBCPP_ENABLE_FILESYSTEM_OVERLOADS
     _LIBCPP_AVAILABILITY_FILESYSTEM _LIBCPP_INLINE_VISIBILITY
     basic_filebuf* open(const _VSTD_FS::path& __p, ios_base::openmode __mode) {
       return open(__p.c_str(), __mode);
     }
 #endif
     inline _LIBCPP_INLINE_VISIBILITY
     basic_filebuf* __open(int __fd, ios_base::openmode __mode);
 #endif
#ifndef _LIBCPP_HAS_NO_GLOBAL_FILESYSTEM_NAMESPACE
     _LIBCPP_INLINE_VISIBILITY
     explicit basic_ifstream(const char* __s, ios_base::openmode __mode = ios_base::in);
 #ifdef _LIBCPP_HAS_OPEN_WITH_WCHAR
     _LIBCPP_INLINE_VISIBILITY
     explicit basic_ifstream(const wchar_t* __s, ios_base::openmode __mode = ios_base::in);
 #endif
     _LIBCPP_INLINE_VISIBILITY
     explicit basic_ifstream(const string& __s, ios_base::openmode __mode = ios_base::in);
-#if _LIBCPP_STD_VER >= 17
+#ifdef _LIBCPP_ENABLE_FILESYSTEM_OVERLOADS
     _LIBCPP_AVAILABILITY_FILESYSTEM _LIBCPP_INLINE_VISIBILITY
     explicit basic_ifstream(const filesystem::path& __p, ios_base::openmode __mode = ios_base::in)
       : basic_ifstream(__p.c_str(), __mode) {}
-#endif // _LIBCPP_STD_VER >= 17
+#endif // _LIBCPP_ENABLE_FILESYSTEM_OVERLOADS
 #endif
 #ifndef _LIBCPP_CXX03_LANG
     _LIBCPP_INLINE_VISIBILITY
     basic_ifstream(basic_ifstream&& __rhs);
 
     _LIBCPP_INLINE_VISIBILITY
     basic_ifstream& operator=(basic_ifstream&& __rhs);
 #endif
     _LIBCPP_INLINE_VISIBILITY
     void swap(basic_ifstream& __rhs);
 
     _LIBCPP_INLINE_VISIBILITY
     basic_filebuf<char_type, traits_type>* rdbuf() const;
     _LIBCPP_INLINE_VISIBILITY
     bool is_open() const;
 #ifndef _LIBCPP_HAS_NO_GLOBAL_FILESYSTEM_NAMESPACE
     void open(const char* __s, ios_base::openmode __mode = ios_base::in);
 #ifdef _LIBCPP_HAS_OPEN_WITH_WCHAR
     void open(const wchar_t* __s, ios_base::openmode __mode = ios_base::in);
 #endif
     void open(const string& __s, ios_base::openmode __mode = ios_base::in);
-#if _LIBCPP_STD_VER >= 17
+#ifdef _LIBCPP_ENABLE_FILESYSTEM_OVERLOADS
     _LIBCPP_AVAILABILITY_FILESYSTEM _LIBCPP_INLINE_VISIBILITY
     void open(const filesystem::path& __p,
               ios_base::openmode __mode = ios_base::in) {
       return open(__p.c_str(), __mode);
     }
-#endif // _LIBCPP_STD_VER >= 17
+#endif // _LIBCPP_ENABLE_FILESYSTEM_OVERLOADS
 
     _LIBCPP_INLINE_VISIBILITY
     void __open(int __fd, ios_base::openmode __mode);
 #endif
     _LIBCPP_INLINE_VISIBILITY
     void close();
 
 private:
public:
     explicit basic_ofstream(const char* __s, ios_base::openmode __mode = ios_base::out);
 #ifdef _LIBCPP_HAS_OPEN_WITH_WCHAR
     _LIBCPP_INLINE_VISIBILITY
     explicit basic_ofstream(const wchar_t* __s, ios_base::openmode __mode = ios_base::out);
 #endif
     _LIBCPP_INLINE_VISIBILITY
     explicit basic_ofstream(const string& __s, ios_base::openmode __mode = ios_base::out);
 
-#if _LIBCPP_STD_VER >= 17
+#ifdef _LIBCPP_ENABLE_FILESYSTEM_OVERLOADS
     _LIBCPP_AVAILABILITY_FILESYSTEM _LIBCPP_INLINE_VISIBILITY
     explicit basic_ofstream(const filesystem::path& __p, ios_base::openmode __mode = ios_base::out)
       : basic_ofstream(__p.c_str(), __mode) {}
-#endif // _LIBCPP_STD_VER >= 17
+#endif // _LIBCPP_ENABLE_FILESYSTEM_OVERLOADS
 
 #ifndef _LIBCPP_CXX03_LANG
     _LIBCPP_INLINE_VISIBILITY
     basic_ofstream(basic_ofstream&& __rhs);
 
     _LIBCPP_INLINE_VISIBILITY
     basic_ofstream& operator=(basic_ofstream&& __rhs);
 #endif
     _LIBCPP_INLINE_VISIBILITY
     void swap(basic_ofstream& __rhs);
 
     _LIBCPP_INLINE_VISIBILITY
     basic_filebuf<char_type, traits_type>* rdbuf() const;
     _LIBCPP_INLINE_VISIBILITY
     bool is_open() const;
 #ifndef _LIBCPP_HAS_NO_GLOBAL_FILESYSTEM_NAMESPACE
     void open(const char* __s, ios_base::openmode __mode = ios_base::out);
 #ifdef _LIBCPP_HAS_OPEN_WITH_WCHAR
     void open(const wchar_t* __s, ios_base::openmode __mode = ios_base::out);
 #endif
     void open(const string& __s, ios_base::openmode __mode = ios_base::out);
 
-#if _LIBCPP_STD_VER >= 17
+#ifdef _LIBCPP_ENABLE_FILESYSTEM_OVERLOADS
     _LIBCPP_AVAILABILITY_FILESYSTEM _LIBCPP_INLINE_VISIBILITY
     void open(const filesystem::path& __p, ios_base::openmode __mode = ios_base::out)
     { return open(__p.c_str(), __mode); }
-#endif // _LIBCPP_STD_VER >= 17
+#endif // _LIBCPP_ENABLE_FILESYSTEM_OVERLOADS
 
     _LIBCPP_INLINE_VISIBILITY
     void __open(int __fd, ios_base::openmode __mode);
 #endif
     _LIBCPP_INLINE_VISIBILITY
     void close();
 
 private:
#ifndef _LIBCPP_HAS_NO_GLOBAL_FILESYSTEM_NAMESPACE
     explicit basic_fstream(const char* __s, ios_base::openmode __mode = ios_base::in | ios_base::out);
 #ifdef _LIBCPP_HAS_OPEN_WITH_WCHAR
     _LIBCPP_INLINE_VISIBILITY
     explicit basic_fstream(const wchar_t* __s, ios_base::openmode __mode = ios_base::in | ios_base::out);
 #endif
     _LIBCPP_INLINE_VISIBILITY
     explicit basic_fstream(const string& __s, ios_base::openmode __mode = ios_base::in | ios_base::out);
 
-#if _LIBCPP_STD_VER >= 17
+#ifdef _LIBCPP_ENABLE_FILESYSTEM_OVERLOADS
     _LIBCPP_AVAILABILITY_FILESYSTEM _LIBCPP_INLINE_VISIBILITY
     explicit basic_fstream(const filesystem::path& __p, ios_base::openmode __mode = ios_base::in | ios_base::out)
       : basic_fstream(__p.c_str(), __mode) {}
-#endif // _LIBCPP_STD_VER >= 17
+#endif // _LIBCPP_ENABLE_FILESYSTEM_OVERLOADS
 
 #endif
 #ifndef _LIBCPP_CXX03_LANG
     _LIBCPP_INLINE_VISIBILITY
     basic_fstream(basic_fstream&& __rhs);
 
     _LIBCPP_INLINE_VISIBILITY
     basic_fstream& operator=(basic_fstream&& __rhs);
 #endif
     _LIBCPP_INLINE_VISIBILITY
     void swap(basic_fstream& __rhs);
 
     _LIBCPP_INLINE_VISIBILITY
     basic_filebuf<char_type, traits_type>* rdbuf() const;
     _LIBCPP_INLINE_VISIBILITY
     bool is_open() const;
 #ifndef _LIBCPP_HAS_NO_GLOBAL_FILESYSTEM_NAMESPACE
     void open(const char* __s, ios_base::openmode __mode = ios_base::in | ios_base::out);
 #ifdef _LIBCPP_HAS_OPEN_WITH_WCHAR
     void open(const wchar_t* __s, ios_base::openmode __mode = ios_base::in | ios_base::out);
 #endif
     void open(const string& __s, ios_base::openmode __mode = ios_base::in | ios_base::out);
 
-#if _LIBCPP_STD_VER >= 17
+#ifdef _LIBCPP_ENABLE_FILESYSTEM_OVERLOADS
     _LIBCPP_AVAILABILITY_FILESYSTEM _LIBCPP_INLINE_VISIBILITY
     void open(const filesystem::path& __p, ios_base::openmode __mode = ios_base::in|ios_base::out)
     { return open(__p.c_str(), __mode); }
-#endif // _LIBCPP_STD_VER >= 17
+#endif // _LIBCPP_ENABLE_FILESYSTEM_OVERLOADS
 
 #endif
     _LIBCPP_INLINE_VISIBILITY
     void close();
 
 private:
     basic_filebuf<char_type, traits_type> __sb_;
 };