Error converting relative paths to absolute paths in Windows if relative path has leading slash or backslash

[philwalk]

Version(s)

os-lib release 0.9.1

Describe the bug
The following idiom is intended to convert a relative path to an absolute path:

val abspath = Path(relativeDir, pwd)

On Windows, this idiom fails, due to there being two types of relative path, unlike on other platforms.

Windows paths are described here: windows-file-path-formats. A reference to what might be called rootRelative is here.

To Reproduce

The following code illustrates the problem with rootRelative paths in Windows.

Example code:

    val p1 = java.nio.file.Paths.get("/omg")
    printf("isAbsolute: %s\n", p1.isAbsolute)
    printf("%s\n", p1)
    printf("%s\n", os.Path("/omg"))

Output on Linux or OSX:

isAbsolute: true
/omg
/omg

On Windows:

isAbsolute: false
\omg
java.lang.IllegalArgumentException: requirement failed: \omg is not an absolute path
        at os.Path.<init>(Path.scala:474)
        at os.Path$.apply(Path.scala:426)
        at oslibChek$package$.main(oslibChek.sc:11)
        at oslibChek$package.main(oslibChek.sc)

Expected behaviour
A rootRelative path is supported by java.nio.file.Paths.get() but not by os.Path().

In Windows, calls to java.io.File#isAbsolute are insufficient to determine whether a path is relative to pwd.
A rootRelative path in Windows is relative to the current working drive (an immutable value captured at jvm startup).

There are 3 use-cases when creating a java.nio.file.Path object:

• path is relative - interpret path as immediately below pwd
• path is absolute - java.nio.file.Paths.get(path)
• path is rootRelative - interpret path as relative to the current working drive.