I have a Dockerfile where I use a tmpfs mount for the apt cache. This is because the image is built in a Docker-in-Docker image in CI, so any cache volumes will be removed when the DinD image goes away at the end of the job anyway.

DL3009 shouldn't trigger for this, since the end result is the same: the apt cache is not in the final image.

Example Dockerfile:

FROM debian:12

# PASS
# Received: [DL3009]
# Expected: [DL3009]
RUN apt-get update

# PASS
# Received: []
# Expected: []
RUN --mount=type=cache,target=/var/cache/apt --mount=type=cache,target=/var/lib/apt apt-get update

# FAIL
# Received: [DL3009]
# Expected: []
RUN --mount=type=tmpfs,target=/var/cache/apt --mount=type=tmpfs,target=/var/lib/apt apt-get update

Output:

-:6 DL3009 info: Delete the apt-get lists after installing something
-:16 DL3009 info: Delete the apt-get lists after installing something

Version: Haskell Dockerfile Linter 2.12.1