Lack of both steps and uses isn't flagged as an error

[jsoref]

Describe the bug
A clear and concise description of what the bug is.

To Reproduce
Steps to reproduce the behavior:

1. With this workflow csharp-qltest.yml:

name: "C#: Run QL Tests"

on:
  push:
    paths:
      - "csharp/**"
      - "shared/**"
      - .github/actions/fetch-codeql/action.yml
      - codeql-workspace.yml
    branches:
      - main
      - "rc/*"
  pull_request:
    paths:
      - "csharp/**"
      - "shared/**"
      - .github/workflows/csharp-qltest.yml
      - .github/actions/fetch-codeql/action.yml
      - codeql-workspace.yml
    branches:
      - main
      - "rc/*"

defaults:
  run:
    working-directory: csharp

jobs:
  qlupgrade:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      - uses: ./.github/actions/fetch-codeql
      - name: Check DB upgrade scripts
        run: |
          echo >empty.trap
          codeql dataset import -S ql/lib/upgrades/initial/semmlecode.csharp.dbscheme testdb empty.trap
          codeql dataset upgrade testdb --additional-packs ql/lib
          diff -q testdb/semmlecode.csharp.dbscheme ql/lib/semmlecode.csharp.dbscheme
      - name: Check DB downgrade scripts
        run: |
          echo >empty.trap
          rm -rf testdb; codeql dataset import -S ql/lib/semmlecode.csharp.dbscheme testdb empty.trap
          codeql resolve upgrades --format=lines --allow-downgrades --additional-packs downgrades \
           --dbscheme=ql/lib/semmlecode.csharp.dbscheme --target-dbscheme=downgrades/initial/semmlecode.csharp.dbscheme |
           xargs codeql execute upgrades testdb
          diff -q testdb/semmlecode.csharp.dbscheme downgrades/initial/semmlecode.csharp.dbscheme

  choose-runner:
    runs-on: ubuntu-latest
    outputs:
      mac-12: ${{ vars.use-large-mac-runners-for-speed && 'mac-12-xl' || 'mac-12' }}
      ubuntu-latest: ${{ vars.use-large-linux-runners-for-speed && 'ubuntu-latest-xl' || 'ubuntu-latest' }}
      windows-latest: ${{ vars.use-large-win-runners-for-speed && 'windows-latest-xl' || 'windows-latest' }}

  qltest:
    needs: choose-runner
    runs-on: ${{ needs.choose-runner.outputs.ubuntu-latest }}
    strategy:
      fail-fast: false
      matrix:
        slice: ["1/2", "2/2"]
    steps:
      - uses: actions/checkout@v4
      - uses: ./csharp/actions/create-extractor-pack
      - name: Cache compilation cache
        id: query-cache
        uses: ./.github/actions/cache-query-compilation
        with:
          key: csharp-qltest-${{ matrix.slice }}
      - name: Run QL tests
        run: |
          codeql test run --threads=0 --ram 50000 --slice ${{ matrix.slice }} --search-path extractor-pack --check-databases --check-undefined-labels --check-repeated-labels --check-redefined-labels --consistency-queries ql/consistency-queries ql/test --compilation-cache "${{ steps.query-cache.outputs.cache-dir }}"
        env:
          GITHUB_TOKEN: ${{ github.token }}
  unit-tests:
    strategy:
      matrix:
        os: [ubuntu-latest, windows-2019]
    runs-on: ${{ matrix.os }}
    steps:
      - uses: actions/checkout@v4
      - name: Setup dotnet
        uses: actions/setup-dotnet@v4
        with:
          dotnet-version: 8.0.100
      - name: Extractor unit tests
        run: |
          dotnet test -p:RuntimeFrameworkVersion=8.0.0 extractor/Semmle.Util.Tests
          dotnet test -p:RuntimeFrameworkVersion=8.0.0 extractor/Semmle.Extraction.Tests
          dotnet test -p:RuntimeFrameworkVersion=8.0.0 autobuilder/Semmle.Autobuild.CSharp.Tests
          dotnet test -p:RuntimeFrameworkVersion=8.0.0 "${{ github.workspace }}/cpp/autobuilder/Semmle.Autobuild.Cpp.Tests"
        shell: bash
  stubgentest:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      - uses: ./csharp/actions/create-extractor-pack
      - name: Run stub generator tests
        run: |
          # Generate (Asp)NetCore stubs
          STUBS_PATH=stubs_output
          python3 scripts/stubs/make_stubs_nuget.py webapp Swashbuckle.AspNetCore.Swagger 6.5.0 "$STUBS_PATH"
          rm -rf ql/test/resources/stubs/_frameworks
          # Update existing stubs in the repo with the freshly generated ones
          mv "$STUBS_PATH/output/stubs/_frameworks" ql/test/resources/stubs/
          git status
          codeql test run --threads=0 --search-path extractor-pack --check-databases --check-undefined-labels --check-repeated-labels --check-redefined-labels --consistency-queries ql/consistency-queries -- ql/test/library-tests/dataflow/flowsources/aspremote
        env:
          GITHUB_TOKEN: ${{ github.token }}

2. Look at the choose-runner job

Expected behavior

According to GitHub, this job isn't valid:
https://github.com/jsoref/codeql/actions/runs/7712430252

Invalid workflow file: .github/workflows/csharp-qltest.yml#L1
No steps defined in steps and no workflow called in uses for the following jobs: choose-runner

Generally if a workflow isn't valid, this extension will complain, e.g. if I add just steps::

Screenshots
Invalid workflow file: .github/workflows/csharp-qltest.yml#L1
No steps defined in steps and no workflow called in uses for the following jobs: choose-runner

Extension Version
v0.26.2

Additional context

[muzimuzhi]

actionlint (https://github.com/rhysd/actionlint) does a good job in detecting empty steps, see here.

There's also a VScode extension for actionlint (I didn't use it myself):
https://marketplace.visualstudio.com/items?itemName=arahata.linter-actionlint.

[dragonfleas]

I was looking for a bug I'm encountering and I came across this issue, this actually isn't a bug, because you can call a reusable workflow from a job and omit steps: an example of this is described here: https://docs.github.com/en/actions/sharing-automations/reusing-workflows#using-a-matrix-strategy-with-a-reusable-workflow

This means that there are situations where steps can be omitted, but this checker probably needs to be smarter and only allow omission if uses has a value.

[jsoref]

It's a bug that the specific workflow isn't flagged as in error-- you're right that the initial summary wasn't strict enough about the conditions, although the body of the issue should have been sufficient for any engineer working on it. I've updated the summary.

[muzimuzhi]

I proposed a fix, see actions/languageservices#98.