[sferik]

As discussed on ruby-oauth/oauth2#780, this adds Duel to the kettle-jem template, so any templated project can opt in and re-templating keeps it. It's off by default: workflows.duel: true turns it on, next to workflows.recording, and it only applies to the full profile. With it off, nothing kettle-jem generates changes.

With Duel on, the template generates .github/workflows/perf.yml, gemfiles/modular/duel.gemfile (Duel and StackProf on Ruby 3.4 or later only), a perf appraisal, the root Gemfile's eval_gemfile for local development, a rake duel task with a stub for older Rubies, the RuboCop include for .duel.rb, and the badge at the end of the badge row. .duel.rb is only copied when it's missing, since it's the project's, and no benchmarks are generated. The workflow is the one from oauth2's PR after review: a read-only Duel job, a separate Comment job with only pull-requests: write that runs none of the branch's code, and the baseline's Ruby (and its bundle) installed for every kind of run when its version file names a different Ruby. It follows the template's conventions for pins, the [ci skip] guard and permissions.

The new spec covers absent and false rendering identically, a project's own Duel files being left alone while it's off, every generated file with it on, a second run changing nothing, an existing .duel.rb and perf appraisal being kept, the profile gating and the changelog transfer filter. I also ran it against oauth2: with Duel off the output matches main's kettle-jem except the lock file's checksums, and with it on every Duel file matches what oauth2's PR ends up with. The rest of the suite has the same six failures here as main (a fixture outside the repo, and the case-insensitive macOS filesystem), and rubocop_gradual:check flags appraisal_helper_and_token_spec.rb, which this doesn't touch.

A few things you may want to weigh in on:

• Adding actions/download-artifact to the pin table means kettle-jem will also update that pin in a project's own workflows, even with Duel off.
• The badge is reference-style, to match the rest of the row.
• Concurrency only cancels superseded pull request runs, so no push to main skips its comparison.
• It uses ruby/setup-ruby rather than setup-ruby-flash, because the baseline steps need its ruby-prefix output.
• The push trigger is main only, not *-stable.
• Turning Duel off again doesn't remove what it generated.
• I couldn't check whether the kettle-jem-appraisals plugin keeps the injected perf block.

Once there's a release with this, I'll update oauth2's PR to just set workflows.duel: true and drop its workarounds.

[pboling]

Adding actions/download-artifact to the pin table means kettle-jem will also update that pin in a project's own workflows, even with Duel off.

Not an issue! The template always updates workflows it can process, and the templated release tooling has a hard fail-closed gate when outdated workflow pins are discovered... So updating them is already a requirement.

I'll fix CI issues.