Feature request: Allow specifying subdirectory with default git context

[PiDelport]

When using git repository contexts, Docker allows specifying a subdirectory using the syntax <repo>#<ref>:<subdir>, as documented here:

• https://docs.docker.com/engine/reference/commandline/build/#git-repositories

BuildKit used to not support this feature, but as of BuildKit 0.9.0, it does:

• Release notes: https://github.com/moby/buildkit/releases/tag/v0.9.0
• Add support for subdirectories when building from git source moby/buildkit#1684
• git: support subdir component moby/buildkit#2116

Can this action add support for this, to avoid the need to use checkouts to build subdirectories?

Workaround

For the time being, specifying a full git context seems to work; for example, to build subdirectory spam:

      - uses: docker/build-push-action@v2
        with:
          context: "https://github.com/${{ github.repository }}.git#${{ github.sha }}:spam"

However, this doesn't use the same logic for determining the default git context as the action does, so it might be fragile.

[PiDelport]

Related issues:

• Checkout isn’t working #120
• Build from Dockerfile in subdirectory #169
• One dir manage multi images . #346
• How to change the Context to other dir? #365

[crazy-max]

@PiDelport

However, this doesn't use the same logic for determining the default git context as the action does, so it might be fragile.

Indeed. I guess we could provide a magic var for this, then you could do:

      - uses: docker/build-push-action@v2
        with:
          context: "{{defaultContext}}:spam"

[dimaqq]

IMO this is still way too hard to get right...

1. when does specifying context: ... require explicit checkout step? always? sometimes?
2. when things go wrong, build fails with mysterious failed to fetch remote 😕

Ideally the UX could be something like this:

• in local checkout you do cd some/sub/dir; docker build .
• in the GHA, specify e.g. subdir: some/sub/dir

Or maybe:

• in local I ran docker build -t xx -f subdir/docker/Dockerfile subdir
• in the GHA, I'd specify file: subdir/docker/Dockerfile and path: subdir

[igorcosta]

The suggested workaround doesn't work for private repos.

      - uses: docker/build-push-action@v2
        with:
          context: "https://github.com/${{ github.repository }}.git#${{ github.sha }}:spam"

When I tried this, I get the following error.

Error: buildx failed with: error: failed to solve: failed to read dockerfile: failed to fetch remote 

I suspect because it's a private repository, it doesn't work. I guess will work only with public repos.

[PiDelport]

Yes, for private repositories, you'll probably need to add credentials from an appropriate environment variable to the URL.

[simensol]

@PiDelport Do you have an example on how to add credentials to the URL?

[karm435]

@simensol you can use this for Private repos

with:
  push: true
  tags: user/app:latest
  secrets: |
      GIT_AUTH_TOKEN=${{ secrets.MYTOKEN }}