"failed to read dockerfile" error with submodules, dockerfiles and buildx

[spmason]

Description

I have a reasonably complicated project that uses Maven submodules and Dockerfiles for builds. This works fine without the new buildx configuration but breaks using it. It crashes out with the following error:

[INFO] DOCKER> WARNING: No output specified for docker-container driver. Build result will only remain in the build cache. To push result image into registry use --push or to load image into docker use --load
[INFO] DOCKER> WARNING: local cache import at ......./dmp-buildx-bug/module1/target/docker/dmp-buildx-bug/cache not found due to err: could not read ....../dmp-buildx-bug/module1/target/docker/dmp-buildx-bug/cache/index.json: open ....../dmp-buildx-bug/module1/target/docker/dmp-buildx-bug/cache/index.json: no such file or directory
[INFO] DOCKER> error: failed to solve: failed to read dockerfile: open /tmp/buildkit-mount3293280157/Dockerfile: no such file or directory
[INFO] DOCKER> docker --config ....../dmp-buildx-bug/module1/target/docker/dmp-buildx-bug/docker buildx rm dmp_dmp-buildx-bug

I've simplified my config into a repo that can reproduce the issue with a simple mvn clean package: https://github.com/spmason/dmp-buildx-bug

Note that commenting out the <buildx> or <dockerFile> config gets past the error. The same config also works for single-module projects

Info

• docker-maven-plugin version : 0.40.0
• Maven version (mvn -v) :

Apache Maven 3.8.4 (9b656c72d54e5bacbed989b64718c159fe39b537)
Maven home: /usr/local/Cellar/maven/3.8.4/libexec
Java version: 11.0.12, vendor: Homebrew, runtime: /usr/local/Cellar/openjdk@11/11.0.12/libexec/openjdk.jdk/Contents/Home
Default locale: en_GB, platform encoding: UTF-8
OS name: "mac os x", version: "12.3.1", arch: "x86_64", family: "mac"

• Docker version : Docker Desktop 4.8.2 (MacOS 12.3.1) (it also fails on our Linux build nodes so it's not mac-specific)
• If it's a bug, how to reproduce : Download the repo and run mvn clean package
• If it's a feature request, what is your use case : N/A
• Sample project : https://github.com/spmason/dmp-buildx-bug.git

[rohanKanojia]

cc @chonton Could you please take a look into this?