tox.ini [DOCKER_BUILDKIT=1]: Do not attempt to retrieve a failed container from buildkit

Author: Matthias Koeppe

tox.ini

@@ -756,7 +756,7 @@ commands =
     docker:            BUILD_IMAGE=$DOCKER_PUSH_REPOSITORY$BUILD_IMAGE_STEM-$docker_target; \
     docker:            BUILD_TAG={env:DOCKER_TAG:$(git describe --dirty --always)}; \
     docker:            TAG_ARGS=$(for tag in $BUILD_TAG {env:EXTRA_DOCKER_TAGS:}; do echo --tag $BUILD_IMAGE:$tag; done); \
-    docker:            DOCKER_BUILDKIT={env:DOCKER_BUILDKIT:0} \
+    docker:            DOCKER_BUILDKIT={env:DOCKER_BUILDKIT:0}; \
     docker:            docker build . -f {envdir}/Dockerfile \
     docker:              --target $docker_target \
     docker:              $TAG_ARGS \
@@ -769,12 +769,16 @@ commands =
     docker:              --build-arg TARGETS_OPTIONAL="{env:TARGETS_OPTIONAL:ptest}" \
     docker:              {env:EXTRA_DOCKER_BUILD_ARGS:}; status=$?; \
     docker:            if [ $status != 0 ]; then \
-    docker:              BUILD_TAG="$BUILD_TAG-failed"; docker commit $(docker ps -l -q) $BUILD_IMAGE:$BUILD_TAG; PUSH_TAGS=$BUILD_IMAGE:$BUILD_TAG; \
+    docker:              if [ $DOCKER_BUILDKIT = 0 ]; then \
+    docker:                BUILD_TAG="$BUILD_TAG-failed"; docker commit $(docker ps -l -q) $BUILD_IMAGE:$BUILD_TAG; PUSH_TAGS=$BUILD_IMAGE:$BUILD_TAG; \
+    docker:              else \
+    docker:                unset BUILD_TAG; unset PUSH_TAGS; echo "DOCKER_BUILDKIT=1, so we cannot commit and tag the failed image"; \
+    docker:              fi; \
     docker:            else \
     docker:              PUSH_TAGS=$(echo $BUILD_IMAGE:$BUILD_TAG; for tag in {env:EXTRA_DOCKER_TAGS:}; do echo "$BUILD_IMAGE:$tag"; done); \
     docker:            fi; \
     docker:            echo $BUILD_IMAGE:$BUILD_TAG >> {envdir}/Dockertags; \
-    docker:            if [ x"{env:DOCKER_PUSH_REPOSITORY:}" != x ]; then \
+    docker:            if [ x"{env:DOCKER_PUSH_REPOSITORY:}" != x -a x"$PUSH_TAGS" != x ]; then \
     docker:              echo Pushing $PUSH_TAGS; \
     docker:              for tag in $PUSH_TAGS; do \
     docker:                docker push $tag || echo "(ignoring errors)"; \