Allow copy elision in path concatenation

[xbolva00]

Summary

Just port of libstdc++'s fix to libc++ fs: https://github.com/gcc-mirror/gcc/commit/e6ac4004fe49d785c63bf87aec4b095b5ce1d19f

Author of fix: Jonathan Wakely

[xbolva00]

Can anybody give me advice from where to generate patch? I do it from libcxx.

[smeenai]

Generating the patch from libc++ is fine (and this patch looks like it has sane paths).

[xbolva00]

In D46593#1091732, @smeenai wrote:

Generating the patch from libc++ is fine (and this patch looks like it has sane paths).

Thank you

[chandlerc]

Sorry folks, but you can't just take patches to libstdc++ and apply them to libc++.

These libraries have different licenses, and so the author of the patch (Jonathan Wakely in this case) need's to *explicitly* contribute that patch to libc++ under libc++'s license. (Or potentially an employer who owns the rights to it.)

So this needs to be reverted, or Jonathan needs to hop on this thread and very explicitly give permission to relicense this and contribute it to LLVM. Generally, I would strongly encourage the original authors making contributions as it simplifies everything.

[xbolva00]

Ping @jwakely

[jwakely]

@chandlerc thanks for catching this.

As the original author I agree to contribute this patch to libc++ under the terms of the MIT and the University of Illinois licences, and under the terms of "Apache 2 with LLVM exception" if necessary in future.

This permission applies only to this patch, not any other code from GCC.

[chandlerc]

In D46593#1093758, @jwakely wrote:

@chandlerc thanks for catching this.

As the original author I agree to contribute this patch to libc++ under the terms of the MIT and the University of Illinois licences, and under the terms of "Apache 2 with LLVM exception" if necessary in future.

This permission applies only to this patch, not any other code from GCC.

Thanks so much for the fast response! And yeah, let's try to follow a more obvious process in the future. =D

libcxx/trunk/include/experimental/filesystem

 { return __lhs.compare(__rhs) > 0; }
 
 inline _LIBCPP_INLINE_VISIBILITY
 bool operator>=(const path& __lhs, const path& __rhs) _NOEXCEPT
 { return __lhs.compare(__rhs) >= 0; }
 
 inline _LIBCPP_INLINE_VISIBILITY
 path operator/(const path& __lhs, const path& __rhs) {
-    return path(__lhs) /= __rhs;
+    path __result(__lhs);
+    __result /= __rhs;
+    return __result;
 }
 
 template <class _Source>
 _LIBCPP_INLINE_VISIBILITY
 typename enable_if<__is_pathable<_Source>::value, path>::type
 u8path(const _Source& __s){
     static_assert(is_same<typename __is_pathable<_Source>::__char_type, char>::value,
         "u8path(Source const&) requires Source have a character type of type 'char'");