Drive letters get duplicated when resolving Windows file: URL with base

[felixfbecker]

It seems like it's impossible to resolve a Windows file:/// URI with a base.

Expected (as implemented Chrome):

new URL('/c:/foo/bar', 'file:///c:/baz/qux').href
"file:///C:/foo/bar"

Actual (as implemented in jsdom/whatwg-url, NodeJS 7, Edge):

new URL('/c:/foo/bar', 'file:///c:/baz/qux').href
'file:///c:/c:/foo/bar'

[annevk]

Windows drive letters are somewhat magical (and act like hosts) so that's somewhat to be expected.

[felixfbecker]

Why do they act like hosts? A file: URI can have a host before the path, the path starts with a leading slash just like on other OS. It's just like a mounted drive on Linux.

The drive letter definitely is not shown as a host in any implementation I tested:

new URL('/c:/foo/bar', 'file:///c:/baz/qux').host
''

Is this behaviour defined in the current spec?

[annevk]

Act like host doesn't mean exposed as one. It just means that when resolving URLs they act like a base.

new URL('/test', 'file:///c:/x').href
"file:///c:/test"

[rmisev]

I think a drive letter must act like "host" in the input as well. I.e. if input has a drive letter, then don't copy the drive letter from base. Because the same is done with hosts: if input contains a host, then host isn't copied from the base.

So I think @felixfbecker is right. It looks like spec. bug.