`weakly_canonical()` throws `The system cannot find the file specified` for some paths containing `..` on Windows

[cameel]

I found a few examples of paths that make weakly_canonical() throw an exception with the following message on Windows:

boost::filesystem::weakly_canonical: The system cannot find the file specified

Here are the paths that trigger this (they do not actually exist in the filesystem):

1. /a/../a/b/
2. a/../a/b/
3. /../a/..
4. /../../a/../

I'd expect weakly_canonical() to return /a/b/ in cases (1) and (2) and / in cases (3) and (4) and this is what happens on other platforms.

Environment

I tested this on Linux (Arch Linux and Ubuntu 20.04), macOS 10.15 and Windows 10.

The Windows is the only platform where I get an exception. I checked boost 1.74.0 and 1.76.0. The environment is a Windows container running on CircleCI and reporting this version:

OS Name:                   Microsoft Windows Server 2019 Datacenter
OS Version:                10.0.17763 N/A Build 17763

Repro

Here's a simple program I used to test this:

#include <array>
#include <iostream>
#include <boost/filesystem.hpp>

using namespace std;
using namespace boost::filesystem;

int main()
{
    array<path, 4> samples = {
        "/a/../a/b/",
        "a/../a/b/",
        "/../a/..",
        "/../../a/../",
    };
    for (path const& sample: samples)
    {
        cout << "Path: " << sample << "; ";
        try
        {
            cout << "weakly_canonical = " << weakly_canonical(sample) << endl;
        }
        catch (exception const& error)
        {
            cout << "EXCEPTION: " << error.what() << endl;
        }
    }
    return 0;
}

Output on Windows

Path: "/a/../a/b/"; weakly_canonical = EXCEPTION: boost::filesystem::weakly_canonical: The system cannot find the file specified
Path: "a/../a/b/"; weakly_canonical = EXCEPTION: boost::filesystem::weakly_canonical: The system cannot find the file specified
Path: "/../a/.."; weakly_canonical = EXCEPTION: boost::filesystem::weakly_canonical: The system cannot find the file specified
Path: "/../../a/../"; weakly_canonical = EXCEPTION: boost::filesystem::weakly_canonical: The system cannot find the file specified

Output on other platforms

Path: "/a/../a/b/"; weakly_canonical = "/a/b/."
Path: "a/../a/b/"; weakly_canonical = "a/b/."
Path: "/../a/.."; weakly_canonical = "/"
Path: "/../../a/../"; weakly_canonical = "/."

[Lastique]

Thanks for the report.

[cameel]

That was fast. Thanks!