Add environment variable to force windows parsing style of volume paths

[shin-]

Fixes #5371

Users can set COMPOSE_FORCE_WINDOWS_HOST=1 to parse volumes and normalize paths as if working from a WIndows host, even if Compose is running on a UNIX system.

[shin-]

cc @StefanScherer if you can give this a whirl, that'd be awesome!

[StefanScherer]

Thanks. I compiled the Darwin binary, but I still see this error:

Without any environment variable:

$ ~/code/compose/dist/docker-compose-Darwin-x86_64 up
ERROR: Volume C:\\Users\\stefan\\.ssh:C:\\ssh has incorrect format, should be external:internal[:mode]

With COMPOSE_FORCE_WINDOWS_HOST=1

$ COMPOSE_FORCE_WINDOWS_HOST=1 ~/code/compose/dist/docker-compose-Darwin-x86_64 up
Creating composeissue5371_test_1 ... error

ERROR: for composeissue5371_test_1  Cannot create container for service test: invalid volume spec "C:\\\\ssh": invalid volume specification: 'C:\\ssh'

ERROR: for test  Cannot create container for service test: invalid volume spec "C:\\\\ssh": invalid volume specification: 'C:\\ssh'
ERROR: Encountered errors while bringing up the project.

I also tried a Windows build from inside the Win2016 VM, but I also see error, both with short and long variant and without and with the environment variable set.

C:\Users\stefan\code\dockerfiles-windows\compose-issue-5371>build\docker-compose-Windows-x86_64.exe up
Creating composeissue5371_test_1 ... error

ERROR: for composeissue5371_test_1  Cannot create container for service test: invalid volume spec "C:\\\\ssh": invalid volume specification: 'C:\\ssh'

ERROR: for test  Cannot create container for service test: invalid volume spec "C:\\\\ssh": invalid volume specification: 'C:\\ssh'
ERROR: Encountered errors while bringing up the project.

I think this should be solved without additional environment variables that the user has to define and know of. Instead docker-compose should recognise the Docker server platform.

[shin-]

Have you tried using single backslashes? In my tests the double slashes weren't necessary. The error you get from the server seems to indicate that as well.

I think this should be solved without additional environment variables that the user has to define and know of. Instead docker-compose should recognise the Docker server platform.

I considered it, but there are some architectural limitations that make this complicated. Specifically, it would mean docker-compose config could not be an offline operation anymore. We can reevaluate, but the environment variable is a good compromise in the meantime.

[StefanScherer]

Woot woot!

$ COMPOSE_FORCE_WINDOWS_HOST=1 ~/code/compose/dist/docker-compose-Darwin-x86_64 up
Creating composeissue5371_test_1 ... done
Attaching to composeissue5371_test_1
test_1  | Microsoft Windows [Version 10.0.14393]
test_1  | (c) 2016 Microsoft Corporation. All rights reserved.
test_1  | 
test_1  | C:\>composeissue5371_test_1 exited with code 0

Oh and it works with docker-compose 1.18.0 as well

$ docker-compose up
Starting composeissue5371_test_1 ... done
Attaching to composeissue5371_test_1
test_1  | Microsoft Windows [Version 10.0.14393]
test_1  | (c) 2016 Microsoft Corporation. All rights reserved.
test_1  | 
test_1  | C:\>composeissue5371_test_1 exited with code 0

$ cat docker-compose.yml 
version: "3.2"

services:
  test:
    image: microsoft/windowsservercore
    volumes:
      - type: bind
        source: C:\Users\stefan\.ssh
        target: C:\ssh

networks:
  default:
    external:
      name: nat

Will add some comments in #5371

[StefanScherer]

So it already works without setting an environment variable with 1.18.0, but with the extended syntax and natural looking single backslashes. 🎉
Is there a way to make the short syntax work as well?

[sgammill]

@StefanScherer

I think this should be solved without additional environment variables that the user has to define and know of. Instead docker-compose should recognise the Docker server platform.

I often use docker-compose config to combine .yml files, and that does not involve connecting to a Docker server. Yes, Compose could (should?) auto-detect the server platform without a client-side flag, but for config, I think some client-side mechanism would be needed.

[shin-]

Short syntax should work with the flag and single slashes.

[jimgolfgti]

@shin- It looks like this PR may have broken some mounts when used under Docker for Windows. Have a look at docker/for-win#1829 for details.

[shin-]

@jimgolfgti This change was made in 1.19.0, which was already included in Docker For Windows 18.02.0-ce. As a result, it's probably not the cause of the issue.

That said, I'll look through the changes we made in 1.20 and see if there's anything else that could have caused the issue.