BUILDKIT_INLINE_CACHE not added to docker buildx build command for Image-Based builds

[ross-p-smith]

When you define a devcontainer with the following devcontainer.json

{
  "build": {
    "dockerfile": "Dockerfile"
  }
}

Then when you run devcontainer build this will translate to

docker buildx build --push --build-arg BUILDKIT_INLINE_CACHE=1 . . .

However, if your devcontainer is defined as (example)

{
  "image": "mcr.microsoft.com/devcontainers/python:3.12",
}

Then the BUILDKIT_INLINE_CACHE=1 is not added to the build.

Additionally, I was unaware of this quirk and I had

  - name: Build and push devcontainer cache
    run: |
      devcontainer build \
        --workspace-folder . \
        --image-name ghcr.io/azure-samples/xxxxt:latest \
        --cache-from ghcr.io/azure-samples/xxxxx:latest \
        --cache-to type=inline \
        --push

When I switched over to the Dockerfile mechanism, you will then get a conflict where --cache-to type=inline and 'BUILDKIT_INLINE_CACHE=1' conflict with each other.

I would suggest that BUILDKIT_INLINE_CACHE=1 is added always when Buildkit is enabled. This would mean adding it to containerFeatures.ts - it is already added for singleContainer.ts and dockerCompose.ts to make everything consistent.

Then if someone adds --cache-to type=inline - this doesnt get added to prevent duplication. If they use other types, then this should be added to the command