Windows + Git Bash: volume path woes

[fvsch]

To follow up on issues we've discussed with @supasteev0, about user-configurable paths on Windows, we're using:

• Docker for Windows
• Git for Windows, which comes for Bash and SSH ("Git Bash").

When trying to define Windows paths for volumes in docker-compose.config.sh and use them dynamically in docker-compose.yml, with this syntax:

  volumes:
    - "$DOCKER_WWW_ROOT:/var/www"

We're getting this error:

ERROR: for cli Cannot create container for service cli: Invalid volume spec "C": Invalid volume destination path: 'C' mount path must be absolute.

I set out to find how docker-compose resolves the config. In start.sh, I'm adding a "showconf" command:

    showconf)
        $DOCKER_COMPOSE --verbose config
        ;;

For this config:

  volumes:
    - 'd:/Dev/www:/var/www'
    # Both variables set to the values show above
    - "$DOCKER_WWW_ROOT:$DOCKER_WWW_DEST"
    # In Git Bash, that variable is, e.g.: /tmp/ssh-cJ59v8lPx0K4/agent.4640
    # (Knowing that Windows doesn't have a "/tmp" path, that's a virtual path of sorts.)
    - "$SSH_AUTH_SOCK:/ssh-agent"

Once resolved, the config is:

  volumes:
    - /d/Dev/www:/var/www:rw
    - /d/Dev/www:C:/Program Files/Git/var/www/
    - /c/Users/USERNA~1/AppData/Local/Temp/ssh-cJ59v8lPx0K4/agent.4640:/ssh-agent:rw

Lessons:

• docker-compose adds the default ":rw" flag if another one (e.g. ":ro") was not set already.
• 'd:/Dev/www' gets resolved to /d/Dev/www. Alright.
• Apparently in Git Bash the /tmp directory is an alias for ~/AppData/Local/Temp
• Finally, Git Bash resolves our $DOCKER_WWW_DEST var as C:/Program Files/Git/var/www/, which is a compatibility feature it has for other reasons. And that's the part that was breaking our config!

So if I change our config to:

  volumes:
    - "$DOCKER_WWW_ROOT:/var/www"

Everything works fine.

Maybe changing the frontend template to hardcode container-side paths would be enough to fix this?

[fvsch]

(Just realized adding the showconf command was not necessary and I could just do ./stack.sh config.)

[supasteev0]

@fvsch frontend template has been updated with hardcoded /var/www path