"add-matcher" doesn't work from within a Docker container

[TrueBrain]

Describe the bug
#56 (comment) suggests that "add-matcher" works from within a Docker container. I couldn't find a way to get this to work. "add-matcher" always uses the host file-system to lookup the file, and can't read a file from the Docker container (that I could find).

To Reproduce
See https://github.com/TrueBrain/actions-flake8/blob/initial_work/entrypoint.sh#L5.
Removing the cp on line 4 and use flake8-matcher.json instead of the full path on line 5. This will result in a "file not found" error.

Expected behavior
"add-matcher" to work from within a Docker container.

Additional context
Honestly, I can fully understand that "add-matcher" uses the host file-system. So maybe this is not a bug or unexpected.

The main thing that is puzzling me a bit, is that the comment linked suggests it should work. But I couldn't find any example of this, and the documentation doesn't talk about this. So I am not sure. As a result: this ticket, in the hope one of you can shed some light on this topic :)

If the cp is the expected solution, I would love to get some pointers what a good folder is to copy this to. Using the workflow folder for this feels a bit ugly.
Or possibly my solution is just completely bananas, and you have a much better solution in mind.

Tnx!

[dnorth98]

I had exactly the same problem when I was putting together an action for Rubocop (https://github.com/rewindio/github-action-rubocop). I ended up having to copy the matcher json to the host in my script:

# With problem matchers in a container, the matcher config MUST be available outside the container on the VM
# So we will just copy it into the workspace

matcher_path=`pwd`/rubocop-problem-matcher.json
cp /rubocop-problem-matcher.json "$matcher_path"

# Note here that we do not use the matcher-path since this is a bind mount into the container
# and is not the same path outside the container on the VM.  Instead, just use current dir
echo "::add-matcher::rubocop-problem-matcher.json"   

It works but feels a bit hacky. Would sure be nice if the matcher could be read inside the container.

[bbugh]

@dnorth98 thank you so much for this tip. I was banging my head against the wall trying every configuration I could think of to get it to find the file. It would be better not to hack it, and I'm happy to just have the action working for now.

[ericsciple]

$RUNNER_TEMP should also work. Basically it has to be copied to one of the mapped directories since the runner is running on the host.

[ericsciple]

Updated docs too early #341 with the guidance:

cp /eslint-compact.json "$HOME/"
echo "::add-matcher::$HOME/eslint-compact.json

However, bug in the runner preventing that from working. Fixed the bug just now actions/runner#331 . After the new runner rolls out (sometime over next couple weeks), will restore guidance in docs.

[TrueBrain]

Been a while, but I finally got to testing the $HOME solution. Works like a charm :) Thank you very much!