path.posix.relative returns different results for *nix and Windows versions of node

[usergenic]

• Version: 8.1.1
• Platform: Windows Server
• Subsystem: path.js

This code returns different values depending on whether run on *nix or windows:

path.posix.relative('a/b/c', '../../x');
'../../../..../x' // on windows
'../../../../../x' // on *nix

[vsemozhetbyt]

On Windows, Node.js versions differ:

  // Node.js 4.8.3 (v8 4.5.103.47) x64

../../../.././x

  // Node.js 6.11.0 (v8 5.1.281.102) x64

../../../..../x

  // Node.js 8.1.1 (v8 5.8.283.41) x64

../../../..../x

[DuanPengfei]

I will try to fix it.

[DuanPengfei]

After reading the code found path.posix.relative call posix.resolve first convert path into an absolute path, but posix.resolve's all the parameters have not yet generated an absolute path then it will add the current path to generate the absolute path. Because of current path is platform-related, I think the direct use of path.posix.relative on Windows is not very suitable. And in the debugging of this problem I found the doc of path.relative is not strict, so I also have a PR doc: make path.relative stricter. So I have confusion about this issue, @gibfahn @XadillaX have some advices?

[refack]

The first solution that comes to mind is adding a check (re #13714): if explicitly running the posix variant of path.posix.relative on a Windows platform, throw a TypeError.
More correct (check resolve): if explicitly running the posix variant of path.posix.resolve on a Windows platform, throw a TypeError

[XadillaX]

@DuanPengfei you may create a new PR to check and throw error in posix.resolve.

[DuanPengfei]

👌🏻I will create a new PR.