Parallel build issue

[Lapshin]

Hi there,

I found if build multiple images in parallel with docker-plus, it runs into an issue - images built incorrectly. A simple example:

Directories:

- image1
  - Dockerfile
- image2
  - Dockerfile

image1/Dockerfile

# syntax = edrevo/dockerfile-plus
FROM debian:jessie

ARG MY_ARG=1111
RUN sleep 5
RUN echo 111 $MY_ARG

image2/Dockerfile

# syntax = edrevo/dockerfile-plus
FROM debian:jessie

ARG MY_ARG=2222
RUN sleep 5
RUN echo 222 $MY_ARG

Now execute 2 terminals and simultaneously run:

DOCKER_BUILDKIT=1 docker build  -t image1 . -f image1/Dockerfile
DOCKER_BUILDKIT=1 docker build  -t image2 . -f image2/Dockerfile

The logs from terminals:
image1

alex@alex-p15s:~/git/esp-dockerfiles$ DOCKER_BUILDKIT=1 docker build  -t image1 . -f image1/Dockerfile
[+] Building 0.4s (10/10) FINISHED                                                                                                                                                                         
 => [internal] load build definition from Dockerfile                                                                                                                                                  0.0s
 => => transferring dockerfile: 146B                                                                                                                                                                  0.0s
 => [internal] load .dockerignore                                                                                                                                                                     0.0s
 => => transferring context: 2B                                                                                                                                                                       0.0s
 => resolve image config for docker.io/edrevo/dockerfile-plus:latest                                                                                                                                  0.1s
 => CACHED docker-image://docker.io/edrevo/dockerfile-plus@sha256:d234bd015db8acef1e628e012ea8815f6bf5ece61c7bf87d741c466919dd4e66                                                                    0.0s
 => local://dockerfile                                                                                                                                                                                0.0s
 => => transferring dockerfile: 37B                                                                                                                                                                   0.0s
 => [internal] load metadata for docker.io/library/debian:jessie                                                                                                                                      0.0s
 => [1/3] FROM docker.io/library/debian:jessie                                                                                                                                                        0.0s
 => CACHED [2/3] RUN sleep 5                                                                                                                                                                          0.0s
 => CACHED [3/3] RUN echo 222 2222                                                                                                                                                                    0.0s
 => exporting to image                                                                                                                                                                                0.0s
 => => exporting layers                                                                                                                                                                               0.0s
 => => writing image sha256:77bd3f97932e3a7f47e97658da199c35624f1ee156b93d61d84c4fcde1fdf7f9                                                                                                          0.0s
 => => naming to docker.io/library/image1

image2

alex@alex-p15s:~/git/esp-dockerfiles$ DOCKER_BUILDKIT=1 docker build  -t image2 . -f image2/Dockerfile 
[+] Building 0.9s (10/10) FINISHED                                                                                                                                                                         
 => [internal] load build definition from Dockerfile                                                                                                                                                  0.0s
 => => transferring dockerfile: 146B                                                                                                                                                                  0.0s
 => [internal] load .dockerignore                                                                                                                                                                     0.0s
 => => transferring context: 2B                                                                                                                                                                       0.0s
 => resolve image config for docker.io/edrevo/dockerfile-plus:latest                                                                                                                                  0.6s
 => CACHED docker-image://docker.io/edrevo/dockerfile-plus@sha256:d234bd015db8acef1e628e012ea8815f6bf5ece61c7bf87d741c466919dd4e66                                                                    0.0s
 => local://dockerfile                                                                                                                                                                                0.0s
 => => transferring dockerfile: 37B                                                                                                                                                                   0.0s
 => [internal] load metadata for docker.io/library/debian:jessie                                                                                                                                      0.0s
 => [1/3] FROM docker.io/library/debian:jessie                                                                                                                                                        0.0s
 => CACHED [2/3] RUN sleep 5                                                                                                                                                                          0.0s
 => CACHED [3/3] RUN echo 222 2222                                                                                                                                                                    0.0s
 => exporting to image                                                                                                                                                                                0.0s
 => => exporting layers                                                                                                                                                                               0.0s
 => => writing image sha256:77bd3f97932e3a7f47e97658da199c35624f1ee156b93d61d84c4fcde1fdf7f9                                                                                                          0.0s
 => => naming to docker.io/library/image2                                                                                                                                                             0.0s

As you can see, both images are equal and have the same hash. This is a bug.
The issue does not appear if Dockerfile names are not the same. For example image1/Dockerfile1 and image2/Dockerfile2

I'm not familiar with docker buildkit, but if you have thoughts on how it could be fixed, please post them here