Heroku build failure with `cat: /tmp/<env_dir>/PORT: No such file or directory`

[chrisbobbe]

So far I'm getting a build failure with this output, after I click the "Deploy" button in Heroku.

Output:

-----> Building on the Heroku-20 stack
-----> Using buildpack: http://github.com/chrisbobbe/matterbridge-heroku.git#master
-----> Matterbridge app detected
cat: /tmp/d20210518-50-1ta64pb/PORT: No such file or directory
 !     Push rejected, failed to compile Matterbridge app.
 !     Push failed

It seems to be fixed without causing problems for my use case (a Zulip <-> Slack bridge) if I comment out this line in bin/support/bash_functions.sh; the line was added in 0665e38:

  if [ -d "$env_dir" ]; then
    for e in $(ls $env_dir); do
-     PORT="$(cat $env_dir/PORT)"
+     # PORT="$(cat $env_dir/PORT)"
      echo "$e" | grep -E "$whitelist_regex" | grep -qvE "$blacklist_regex" &&
        port_unexpanded=$(echo "$e=$(cat $env_dir/$e)") &&
        port_expanded=$(eval "echo $port_unexpanded") &&
        export $port_expanded
      :
    done
  fi

Does that seem like a good workaround, or can I expect things to go wrong in mysterious ways? Would it be better to revert 0665e38 entirely? I don't really know what that code is doing, and I haven't been able to determine why $env_dir/PORT might ever exist.