Features implementation breaks buildkit Dockerfile by stripping # syntax=docker/dockerfile:1 line

[davecardwell]

I have a .devcontainer/Dockerfile using buildkit with the starting line, # syntax=docker/dockerfile:1. It has been working for the past several versions of vscode. Since updating to v1.72.0 my devcontainer fails to run.

When starting my devcontainer, vscode runs:
docker-compose --project-namemyproject -f /path/to/compose.yaml -f /Users/me/Library/Application Support/Code/User/globalStorage/ms-vscode-remote.remote-containers/data/docker-compose/docker-compose.devcontainer.build-1665287802265.yml build

That generated config file looks like:

services:
  devcontainer:
    build:
      dockerfile: /var/folders/zf/3lppq14565594kgv2_7chsx40000gn/T/devcontainercli/container-features/0.19.0-1665287801705/Dockerfile-with-features
      target: dev_containers_target_stage
      args:
        - BUILDKIT_INLINE_CACHE=1
        - _DEV_CONTAINERS_BASE_IMAGE=dev_container_auto_added_stage_label
        - _DEV_CONTAINERS_IMAGE_USER=root
        - _DEV_CONTAINERS_FEATURE_CONTENT_SOURCE=dev_container_feature_content_temp

And the dockerfile it references is a modified copy of my original Dockerfile, however the # syntax=docker/dockerfile:1 has been stripped, resulting in the error:
failed to solve: rpc error: code = Unknown desc = failed to solve with frontend dockerfile.v0: failed to create LLB definition: dockerfile parse error line 13: unknown instruction: SET

Modifying the referenced Dockerfile-with-features and adding back in the # syntax=docker/dockerfile:1 allows the build command to proceed from the command line, however vscode will generate a different set of paths if I try to build the container in-app so the issue will repeat.

The specific part of my Dockerfile it is choking on without the # syntax line is a RUN heredoc: https://www.docker.com/blog/introduction-to-heredocs-in-dockerfiles/

Note that I am not actually using Features in my devcontainer.json.

Apologies if this is better suited in the vscode Issues—please direct me to the appropriate repository.

Version: 1.72.0
Commit: 64bbfbf67ada9953918d72e1df2f4d8e537d340e
Date: 2022-10-04T23:19:55.212Z
Electron: 19.0.17
Chromium: 102.0.5005.167
Node.js: 16.14.2
V8: 10.2.154.15-electron.0
OS: Darwin arm64 21.6.0
Sandboxed: No

Dev Containers: v0.255.2


Docker desktop: macOS 4.12.0 (85629)
Engine: 20.10.17
Compose: v2.10.2

[davecardwell]

Closing in favor of microsoft/vscode-remote-release#6848