[Bug] Expression substitution doesn't always work

[roryabraham]

From https://github.com/rhysd/actionlint/blob/main/docs/checks.md#shellcheck-integration-for-run:

Since both ${{ }} expression syntax and ShellScript's variable access $FOO use $, remaining ${{ }} confuses shellcheck. To avoid it, actionlint replaces ${{ }} with underscores. For example echo '${{ matrix.os }}' is replaced with echo '________________'.

Unfortunately, I found an example where this doesn't work:

run: |
  if [[ -z ${{ env.FOO }} ]]; then
    echo "FOO is empty"
  fi

[roryabraham]

Found a workaround but it's not ideal:

run: |
  SOME_VAR=${{ env.FOO }}
  if [[ -z "$FOO" ]]; then
    echo "FOO is empty"
  fi

[rhysd]

Thank you for reporting this. Really nice catch. I will temporarily disable SC2157 then consider how to handle this correctly later.

[rhysd]

I added workaround at 29512f4. Closing.