[TEP0138] Add Per-feature Flag Struct for New Features

[JeromeJu]

Changes

This PR contains 2 commits which:

• refactors the feature-versioning developer doc
• adds the per-feature flag struct and documentations for
  new features in TektonCD pipeline.

part of: TEP-0138

Submitter Checklist

As the author of this PR, please check off the items in this checklist:

• Has Docs if any changes are user facing, including updates to minimum requirements e.g. Kubernetes version bumps
• Has Tests included if any functionality added or changed
• Follows the commit message standard
• Meets the Tekton contributor standards (including functionality, content, code)
• Has a kind label. You can add one by adding a comment on this PR that contains /kind <type>. Valid types are bug, cleanup, design, documentation, feature, flake, misc, question, tep
• Release notes block below has been updated with any user facing changes (API changes, bug fixes, changes requiring upgrade notices or deprecation warnings). See some examples of good release notes.
• Release notes contains the string "action required" if the change requires additional action from users switching to the new release

Release Notes

Please use per feature flags for new API-driven feature gating.

[tekton-robot]

Skipping CI for Draft Pull Request.
If you want CI signal for your change, please convert it to an actual PR.
You can still manually trigger a test run with /test all

[tekton-robot]

The following is the coverage report on the affected files.
Say /test pull-tekton-pipeline-go-coverage-df to re-run this coverage report

File	Old Coverage	New Coverage	Delta
pkg/apis/config/feature_flags.go	91.7%	92.5%	0.9

[tekton-robot]

The following is the coverage report on the affected files.
Say /test pull-tekton-pipeline-go-coverage-df to re-run this coverage report

File	Old Coverage	New Coverage	Delta
pkg/apis/config/feature_flags.go	91.7%	88.8%	-2.9

[chitrangpatel]

There seems to be only one commit but the PR description says two. May be it needs to be updated.

[QuanZhang-William]

/assign

[JeromeJu]

There seems to be only one commit but the PR description says two. May be it needs to be updated.

Thanks @chitrangpatel . Updated!

Also to be on the note for this change: I previously thought that we could just provide an example since there were no upcoming new features yet. But now there are a couple that I've realized: i.e. #7162 and CEL expression that had been mentioned in TEP process.

Happy to pair on/ walk through the process if a new feature is getting in pipeline! cc @tektoncd/core-collaborators

[chitrangpatel]

Do you think we can have an example of how we introduce a feature "enable-foo" in developer docs? In there we can at least provide an example of that we need to do to the struct and how it can be used internally in our codebase. Finally, when we add a new feature, we might want to also enable it in https://github.com/tektoncd/pipeline/blob/main/test/e2e-tests-kind-prow-alpha.env

I think a document showing this journey will be useful when we start adding new features under per-feature flags.

[afrittoli]

/assign

[JeromeJu]

Do you think we can have an example of how we introduce a feature "enable-foo" in developer docs? In there we can at least provide an example of that we need to do to the struct and how it can be used internally in our codebase. Finally, when we add a new feature, we might want to also enable it in https://github.com/tektoncd/pipeline/blob/main/test/e2e-tests-kind-prow-alpha.env

I think a document showing this journey will be useful when we start adding new features under per-feature flags.

Thanks @chitrangpatel , it makes sense to add it as an example. And I totally agree developers dir is the right place to go 🙏

Working on it as a 2nd commit rn.

[tekton-robot]

The following is the coverage report on the affected files.
Say /test pull-tekton-pipeline-go-coverage-df to re-run this coverage report

File	Old Coverage	New Coverage	Delta
cmd/entrypoint/runner.go	86.2%	84.5%	-1.7
pkg/reconciler/pipelinerun/resources/resultrefresolution.go	99.2%	98.3%	-0.8

[JeromeJu]

Since #6941 has been merged and this is unblocked, while we have a handful of new features(i.e. #7277, #7255) that might come in. Could we prioritize merging this PR as the more new feature flags come into the repo the more future "patching" of the usage with the new struct there are going to be? 🙏 🙏 🙏
cc @tektoncd/core-maintainers

[QuanZhang-William]

Thanks for the PR, generally looks good to me. Added some small comments.

[tekton-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: QuanZhang-William, Yongxuanzhang

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[afrittoli]

Thanks @JeromeJu - I left some comments.

[afrittoli]

"All existing features" will sound confusing in future, despite the link.
I find the table a bit difficult to parse, what about this?

Releases	Global flag enable-api-fields	Per-feature flags
Prior to v0.53.0	All API features	Alpha/beta non-API features only
After v0.53.0	Alpha/beta features in v0.53.0	Alpha/beta non-API features and API features introduced after v0.53.0
All alpha/beta features in v0.53.0 become stable or are removed	Sunset enable-api-fields	All alpha/beta API and NON-API features

[JeromeJu]

That makes sense! I made some minor changes to it because behavioural flags will retain their behaviour. (I also added a note below)

[JeromeJu]

Also updated the links at tektoncd/community#1091.

[afrittoli]

/lgtm