Validate usage of double quotes in expressions

Motivation

We use check-jsonschema in https://github.com/Lightning-AI/lightning/ to validate all our workflow files and it works very well. We have a GitHub action for this check here.

Recently we debugged an issue in our configuration that wasn't caught by check-jsonschema. The following yaml had double quotes in the expression:

    - name: Testing Warnings
      # the stacklevel can only be set on >=3.7
      if: ${{ (steps.skip.outputs.continue == '1') && ( matrix.python-version != "3.7" ) }}
      working-directory: tests/tests_pytorch
      # needs to run outside of `pytest`
      run: python utilities/test_warnings.py

which caused an error in the workflow:

The workflow is not valid. .github/workflows/ci-pytorch-test-full.yml (Line: 167, Col: 11): Unexpected symbol: '"3'. Located at position 68 within expression: (steps.skip.outputs.continue == '1') && ( matrix.python-version != "3.7" )

And it should have used single quotes like this:

matrix.python-version != '3.7'

check-jsonschema is useful for us because we can raise these warnings directly to the author in the PR.

Pitch

Would it be possible to have check-jsonschema validate against correct usage of single quotes vs. double quotes? I am not familiar with how check-jsonschema works, whether this is technically possible, or whether this is in the scope of this tool at all.

No file or test is named in the issue. Start by locating check-jsonschema’s GitHub Actions workflow validation entry point and reviewing how expressions are currently handled; done means the reported double-quote usage is detected and surfaced as a warning or validation error.