CodeQL: skip Python analysis when no Python files changed

[Copilot]

The CodeQL workflow runs Python analysis on every PR, failing for codebases like Cyrano that contain no Python. This adds a new detect job to conditionally skip Python analysis when the changeset lacks .py files.

Changes

New detect job:

• Checks out repo with fetch-depth: 0
• Compares changed files for PR (base→head) or push (before→after) events
• Sets python_changed output via $GITHUB_OUTPUT
• Handles edge cases: initial commits, scheduled runs

Modified analyze job:

• Added needs: detect dependency
• Conditional: if: matrix.language != 'python' || needs.detect.outputs.python_changed == 'true'
• Python remains in matrix—analysis runs only when needed

Behavior

Event Type	Python Files Changed	Python Analysis
PR/Push	No	Skipped
PR/Push	Yes	Runs
Schedule	N/A	Runs (checks all files)

Other languages (actions, javascript-typescript) run unconditionally. Other workflows unaffected.

Original prompt

Modify the CodeQL workflow to only run Python analysis when the change set actually contains Python files. The repository's current CodeQL workflow (.github/workflows/codeql.yml) uses a matrix that includes python, which causes the 'CodeQL Advanced / Analyze (python)' check to run (and fail) for PRs that don't touch Python files. Implement a safe conditional so Python analysis runs only when Python files are present in the push or PR.

Changes to make:

• Update .github/workflows/codeql.yml
  • Add a new job detect that checks out the code and determines whether the current event (pull_request or push) includes any changed files with a .py extension. The job should set an output python_changed to true or false using the recommended $GITHUB_OUTPUT approach.
  • Make the existing analyze job depend on detect (add needs: detect) and add a job-level if condition so the python matrix job runs only when matrix.language != 'python' OR needs.detect.outputs.python_changed == 'true'.
  • Keep the existing matrix entries (including python) so the workflow still supports python analysis when needed.
  • Preserve other configuration in the file (permissions, strategy, config-file usage, autobuild, upload, etc.) so behavior for other languages is unchanged.

Implementation details for the detect job:

• runs-on: ubuntu-latest
• steps:
  • uses: actions/checkout@v4 with fetch-depth: 0 (to enable diff between refs)
  • run: a shell script that determines changed files for pull_request vs push and sets the boolean output python_changed via: echo "python_changed=true" >> $GITHUB_OUTPUT or echo "python_changed=false" >> $GITHUB_OUTPUT.
  • The detection should handle pull_request events by comparing the PR head to the base branch, and push events by using github.event.before and github.sha.

Safety notes to include in PR description:

• This change only skips the python analysis when no Python files were touched; it does not remove python from the matrix, so python analysis still runs when Python files exist in a change.
• If there are other workflow files that initialize CodeQL separately, they may still run python analysis; this PR only updates the main .github/workflows/codeql.yml.

Files to modify:

• .github/workflows/codeql.yml

Branch and PR:

• Create a new branch named: ci/conditional-codeql-python
• Commit the change and open a pull request against main with title: "CodeQL: run python analysis only when Python files changed"

PR description must explain what changed and why, include the safety notes above, and reference that this prevents unnecessary failing python analysis runs for Cyrano while preserving Python scans when relevant.

This pull request was created from Copilot chat.

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