Some Windows paths fail to `.absolutize()`

[dlenski]

Based on its API (returns std::io::Result), I assumed that the absolutize() method should either convert a non-absolute path to an absolute path, or return a std::io::Error.

With UnixPath, this appears to hold in 100% of cases.

However, with WindowsPath, there are some exceptions: paths which are not absolute, and are neither transformed into absolute paths by absolutize()… but also don't return errors.

What I've found:

1. \\some.server or \\some.server\share: .is_absolute() is false, but .has_root() is true. Calling .absolutize() returns the path unmodified.
2. "C:" or "C:whatever" (same for any other drive letter): Windows kinda-sorta has a separate cwd for each drive (a legacy of MS-DOS), but typed-path doesn't seem to use this. Both .is_absolute() and .has_root() are false, and calling .absolutize() returns the path unmodified.

What I think should happen for these:

1. \\some.server\share should be considered equivalent to \\some.server\share\, with .is_absolute() being true regardless of whether or not the final \ is included. In the same way that C:\whatever and C:\whatever\ are equivalent when .joining or .pushing further path components.

   On the other hand, \\some.server should return an error when calling .absolutize()

2. A few possibilities:

   • Use GetFullPathNameW to get the per-drive cwd, and use that to absolutize the path…
   • Or it should return an error, something like std::io::Error::other("cannot absolutize a Windows drive without a following backslash")…
   • Or it should just ignore this ancient legacy behavior, and insert the backslash (treating C:foo as equivalent to C:\foo)

#[test]
fn windows_path_absolutize_problem() {
    for p in vec!["C:", "D:whatever"] {
        let p = WindowsPath::new(p);
        let ap = p.absolutize();
        
        if let Ok(ap) = ap {
            assert!(!ap.is_absolute() && !ap.has_root());
            assert_eq!(ap.as_path(), p);
        } else {
            panic!();
        }
    }

    for p in vec![r"\\server.com", r"\\server.com\share"] {
        let p = WindowsPath::new(p);
        let ap = p.absolutize();
        if let Ok(ap) = ap {
            assert!(!ap.is_absolute() && ap.has_root());
            assert_eq!(ap.as_path(), p);
        } else {
            panic!();
        }
    }
}

[dlenski]

#8 and #50 discuss some related issues

[chipsenkbeil]

@dlenski is this resolved now between #62 and #63? Or any remaining work you see being needed? I'll publish a new release once we can close this issue.

[dlenski]

Thank you! From my point of view, it's resolved, with the resolution of the ambiguous Windows paths being simply to return an error (which is both simple and reasonable).

More tests related to Windows path oddities might be useful if anyone finds similar issues…