ONBUILD COPY --from does not work

[andrewrynhard]

Using the following Dockerfiles:

base.dockerfile:

FROM alpine
ONBUILD COPY --from=extra / /extra

extra.dockerfile:

FROM scratch AS extra
COPY --from=alpine /lib /

FROM docker.io/andrewrynhard/base:latest

I am able to get the following to work without buildx:

$ docker build -t docker.io/andrewrynhard/base:latest -f base.dockerfile .
Sending build context to Docker daemon  89.81MB
Step 1/2 : FROM alpine
latest: Pulling from library/alpine
89d9c30c1d48: Pull complete
Digest: sha256:c19173c5ada610a5989151111163d28a67368362762534d8a8121ce95cf2bd5a
Status: Downloaded newer image for alpine:latest
 ---> 965ea09ff2eb
Step 2/2 : ONBUILD COPY --from=extra / /extra
 ---> Running in 882c8bb8dc57
Removing intermediate container 882c8bb8dc57
 ---> 62bab3d925f1
Successfully built 62bab3d925f1
Successfully tagged base:latest
$ docker build -t extra -f extra.dockerfile .
Sending build context to Docker daemon  89.81MB
Step 1/3 : FROM scratch AS extra
 --->
Step 2/3 : COPY --from=alpine /lib /
 ---> b6d5b611c2a2
Step 3/3 : FROM base
# Executing 1 build trigger
 ---> 08c407fa8f46
Successfully built 08c407fa8f46
Successfully tagged extra:latest
$ docker run --rm -it extra:latest find /extra
/extra
/extra/libssl.so.1.1
/extra/ld-musl-x86_64.so.1
/extra/libcrypto.so.1.1
/extra/mdev
/extra/libz.so.1
/extra/apk
/extra/apk/db
/extra/apk/db/lock
/extra/apk/db/scripts.tar
/extra/apk/db/installed
/extra/apk/db/triggers
/extra/libz.so.1.2.11
/extra/libc.musl-x86_64.so.1
/extra/firmware

But this does not work using buildx (using the same docker.io/andrewrynhard/base:latest image):

$ docker buildx build -t extra -f extra.dockerfile --load .
[+] Building 1.4s (7/7) FINISHED
 => [internal] load .dockerignore                                                                                                                                                                          0.0s
 => => transferring context: 2B                                                                                                                                                                            0.0s
 => [internal] load build definition from extra.dockerfile                                                                                                                                                 0.0s
 => => transferring dockerfile: 133B                                                                                                                                                                       0.0s
 => [internal] load metadata for docker.io/andrewrynhard/base:latest                                                                                                                                       1.0s
 => CACHED [stage-1 1/1] FROM docker.io/andrewrynhard/base:latest@sha256:7a28354691d9a0f39a5464a843b3e5777f6dc71bdaae0addb1c905e8a89d43db                                                                  0.0s
 => => resolve docker.io/andrewrynhard/base:latest@sha256:7a28354691d9a0f39a5464a843b3e5777f6dc71bdaae0addb1c905e8a89d43db                                                                                 0.0s
 => [stage-1 2/1] COPY --from=extra / /extra                                                                                                                                                               0.0s
 => exporting to oci image format                                                                                                                                                                          0.3s
 => => exporting layers                                                                                                                                                                                    0.1s
 => => exporting manifest sha256:3e9f962e876a8800177305e375b6970b93a7c9f3a08fa87211dfc8cb7628a968                                                                                                          0.0s
 => => exporting config sha256:655fd9064dc1b13e89fe3de444255e9eb3602d211c536aee9416565f1b9554f9                                                                                                            0.0s
 => => sending tarball                                                                                                                                                                                     0.1s
 => importing to docker                                                                                                                                                                                    0.1s
$ docker run --rm -it extra:latest find /extra
/extra

[tonistiigi]

Thanks for the report. Closing as dupe of moby/buildkit#816