path::lexically_normal() behaves slightly differently from the standard

[Riccardo]

Hi!
First of all, thank you for this library!

Describe the bug
I'm trying to use this library as a fallback when the compiler does not support the final standard version of <filesystem> library.
However, I've found that in some cases the result returned by path::lexically_normal() of ghc is different from the one returned by the C++17 standard version.
In particular, the normal version of path("../") should be "..", while ghc retains the trailing '/' (eventually converted to '\\' on Windows).
On Windows, the same applies also to path("..\\"), which should be normalized to ".." and instead still retains the trailing '\\'.

To Reproduce
To reproduce the behavior, I've created a small program to compare the different results between ghc::filesystem and std::filesystem:

#include <iostream>
#include <filesystem>
#include "ghc/filesystem.hpp"

using std::cout;
using std::endl;

int main() {
    cout << "[std] path(\"../\").lexically_normal() == ";
    cout << std::filesystem::path("../").lexically_normal() << endl;
    
    cout << "[ghc] path(\"../\").lexically_normal() == ";
    cout << ghc::filesystem::path("../").lexically_normal() << endl;

#ifdef _WIN32
    cout << "[std] path(\"..\\\\\").lexically_normal() == ";
    cout << std::filesystem::path("..\\").lexically_normal() << endl;
    
    cout << "[ghc] path(\"..\\\\\").lexically_normal() == ";
    cout << ghc::filesystem::path("..\\").lexically_normal() << endl;
#endif
    return 0;
}

I've tested the program using various compilers and operating systems.

• On Windows 10 using

  • MSVC 2017
  • MinGW-w64 9.2.0
  • clang 9.0
  
  

  the program output is:

  [std] path("../").lexically_normal() == ".."
  [ghc] path("../").lexically_normal() == "..\\"
  [std] path("..\\").lexically_normal() == ".."
  [ghc] path("..\\").lexically_normal() == "..\\"

• On Ubuntu 18.04 LTS using

  • g++ 8.3.0
  • clang 6.0
  
  

  the program output is:

  [std] path("../").lexically_normal() == ".."
  [ghc] path("../").lexically_normal() == "../"

Expected behavior
In all these cases path::lexically_normal() of ghc should return a path("..") in order to conform to the standard.

External References

• std::filesystem::path from cppreference.com

  A path can be normalized by following this algorithm:
  ...
  7. If the last filename is dot-dot, remove any trailing directory-separator.

• Relative Paths from Open Standards

  A path in normal form has no redundant current directory (dot) elements, no redundant parent directory (dot-dot) elements, and no redundant directory-separators.

[Steffen Schümann]

Indeed, that is wrong. I'll look into it this evening, after my daytime job.

Thanks for the detailed report!

[Steffen Schümann]

Okay, fixed it on master. Will also be part of release v1.2.8 (not scheduled yet).

[Riccardo]

Thanks for the detailed report!

You're welcome!

Okay, fixed it on master. Will also be part of release v1.2.8 (not scheduled yet).

Great, thank you!

[Steffen Schümann]

Released with v1.2.8