path.relative on windows returns incorrect result

[TanninOne]

• Version: tested with v7.7.4 and v9.2.0
• Platform: Windows 10 (64-bit)
• Subsystem: path

Code says it best:

> path.relative('c:', 'c:\\test')
'..\\..\\test'
> path.relative('c:', 'c:/test') 
'..\\..\\test'

Not sure why c: is treated differently here, but for all other volumes it returns the right result:

> path.relative('d:', 'd:\\test')
'test'
> path.relative('d:', 'd:/test') 
'test'

also it appears to happen only on the root level:

> path.relative('c:\\test', 'c:\\test\\sub')
'sub'

and only if the colon is the last character of the base path

> path.relative('c:\\', 'c:\\test')
'test'

[vsemozhetbyt]

It also seems to happen only if the current working directory is in c: drive.

[TanninOne]

I can't confirm that:

> process.cwd()
'D:\\'
> path.relative('c:', 'c:\\test')
'..\\..\\test'
> path.relative('d:', 'd:\\test')
'test'

Edit: I just noticed that github had replaced all double backslashes by single ones, in my tests all backslashes were properly escaped.

[vsemozhetbyt]

Hmm. For me, with Node.js 9.2.0 on Windows 7 x64

c:\>node
> process.cwd()
'c:\\'
> path.relative('c:', 'c:\\test')
'test'

c:\Windows>node
> process.cwd()
'c:\\Windows'
> path.relative('c:', 'c:\\test')
'..\\test'

d:\>node
> process.cwd()
'd:\\'
> path.relative('c:', 'c:\\test')
'test'

d:\Boot>node
> process.cwd()
'd:\\Boot'
> path.relative('c:', 'c:\\test')
'test'

[TanninOne]

Oooh, wait, now I get it. When the first parameter is "c:" or "d:" or ":" it uses the cwd in the corresponding drive as reference, not the root directory.

> process.cwd()
'D:\\Temp'
> path.relative('d:', 'd:\\test')
'..\\test'

(remember: windows has a separate cwd for each drive)

[TimothyGu]

When the first parameter is "c:" or "d:" or ":" it uses the cwd in the corresponding drive as reference, not the root directory.

That's correct. You may want to instead use C:\ as root. Do you think this issue could now be closed?

See also: #14405 and #14440 (only applied to v8.3.0+ and v6.11.3 (and later v6.x)).

[TanninOne]

I realize this would be an api change but I believe it would be more intuitive to have C: be treated as the root. Windows api calls like findfirstfile or ntquerydirectoryfile do it. No win api call afaik uses drive specific cwds.

And anyone coming from unixoid oses will also be surprised.
This behaviour is maybe not a Bug but it‘s a BugFactory.
Drive-specific cwds are an abomination, especially since Windows has another, drive independent cwd, and I somehow don‘t believe anyone is writing code expecting this behaviour.

[TimothyGu]

@TanninOne

I believe it would be more intuitive to have C: be treated as the root.
And anyone coming from unixoid oses will also be surprised.

While that may be the case, as a platform-level API we cannot go against well-established and documented traditions on a specific OS. Python, for example, follows the current Node.js behavior:

>>> os.getcwd()
'C:\\Users\\Timothy'
>>> ntpath.relpath('C:\\abc\\def', r'C:')
'..\\..\\abc\\def'
>>> os.chdir('C:\\')
>>> os.getcwd()
'C:\\'
>>> ntpath.relpath('C:\\abc\\def', r'C:')
'abc\\def'

Drive-specific cwds are an abomination

On this, I wholeheartedly agree.

[TanninOne]

Ok, I'll withdraw my report. To my surprise, FindFirstFile also works this way. It's utterly insane but yeah, that's windows alright. :(