Don't convert slashes for UNIX paths on Windows hosts

[shin-]

Fixes #5716
Fixes docker/for-win#1829

[Dimrok]

Shouldn't this be:

-sysnorm = ntpath.normpath if win_host else os.path.normpath
+sysnorm = ntpath.normpath if win_host else posix.normpath

[shin-]

win_host will be true only if COMPOSE_FORCE_WINDOWS_HOST is set. In this case we want to produce NT style paths regardless of the client platform. In all other cases, we want to use the default normalization for the client system, hence the use of os.path.normpath

[Dimrok]

Do we? If you have a compose on Windows talking to a remote linux engine?

[Dimrok]

Just to note everything related to path here:

• docker-compose runs on both Windows- and Unix-based distributions, so os.path.normpath can be either posixpath or ntpath.
• the host can be Linux running Linux containers, Windows running Windows containers and Windows running Linux containers.
• The volume definition can be <linux>:<linux>, <windows>:<linux> and <windows>:<windows>.
• Docker for Widows running a Linux container has a proxy that does some path manipulation and validation:
  • if you write C:/foo/bar:/bar, the proxy will ensure the volume is mounted somewhere (/c/foo/bar) and translate the given path to /mnt/c/foo/bar (where the volume is mounted).
  • if you write /c/foo/bar:/bar, no validation is done but the path is still translated to /mnt/c/foo/bar (we don't want that, because if you forgot to mount the volume, /mnt/c/foo/bar will be created).
  • You can have both Posix and NT path (e.g. /var/run/docker.sock:/var/run/docker.sock and C:\\Users\\toto:/toto) for the same container. Docker for Windows understands absolute Linux path as being part of the host (in this case, bind-mounting the socket) unless they look like /<drive>/..., in this case, they are translate to /mnt/<drive>/....
  • An ill-formed path such as C:/foo/bar is translated to /mnt/c/foo/bar.
• Docker for Windows running Windows containers doesn't manipulate paths.
• Docker for Windows running Linux containers doesn't manipulate paths (to be verified).
• Volume configuration like C:\\Users\\foo:C:\\foo works natively on Docker for Windows using Windows containers.
• You can have multi-arch images so you have to be aware of the host's platform.

The point is: We shouldn't normalize the paths at all. The engine is clever enough to understand what you meant. Or if we really want to (e.g. to change /foo/bar/../shiny to /foo/shiny if we want to be fancy), we shouldn't change the type of paths the user provided.

[shin-]

I think you make a good point about not having to normalize paths ; that said, I'd want to do a thorough check first to make sure we're not breaking anything by doing so, and have a follow-up PR for that specifically. For the time being, if this fixes docker/for-win#1829, let's roll with it.

[Dimrok]

let's roll with it.
👍