ci: only run jobs when relevant files have been changed [actions testing PR]

[agilgur5]

Fixes argoproj#10156
Fixes argoproj#10265

• Note: these can be further segmented and improved as well, see "Future Work" below

Motivation

Make CI run faster for certain kinds of PRs, use less CI minutes (and just reduce unnecessary compute in general), and limit the blast radius of flaky tests as well

• e.g. don't run E2E tests if only UI or only Docs have changed
  • or don't run UI CI when UI has not chaged

Modifications

Changed Files checks

• use tj-actions/changed-files action for this

  • the most popular and full featured one I could find

• run changed-files in its own job that must run before all other jobs

  • have it output booleans for specific changes -- limit all the changed_files nuances, naming, syntax, etc to that one job
    • job outputs are also needed for skipping other jobs, as step outputs can't be directly accessed
      • see https://docs.github.com/en/actions/using-jobs/defining-outputs-for-jobs and https://docs.github.com/en/actions/learn-github-actions/contexts#needs-context

• have other jobs specify it in their needs and then skip if not needed with if

• use multi-output variant of changed-files YAML directive

  • so can check e2e vs lint vs UI etc
  • note that changed-files supports a YAML variant with list anchoring/aliasing

• use any_modified as that includes added, copied, modified, renamed, and deleted (ACMRD)

  • any_changed does not include deletions

Changes to needs for codegen and lint

• both can run independently of each other and independently of tests

  • they should fail fast if the other one fails though, I suppose

• otherwise this breaks some of the checks, since if tests are skipped, then codegen and lint are skipped too

Changes to Status Checks

Note that due to lack of GH features such as actions/runner#952 and https://github.com/orgs/community/discussions/9141, there is a workaround embedded here for the E2E test matrix

• skipping the overall e2e-tests job will cause status checks for individual E2E tests to just hang indefinitely
  • so instead we can change the required status checks to check the new composite result
    • that or we'd have to put an if for every single step of the E2E tests and also check for changed files within each E2E test
      • as there is no early exit feature such as Command to early-exit the job and set check conclusion actions/runner#662
      • as steps can't use outputs from other jobs
      • and even then, the E2E test job would report as "success" instead of "skipped" as there is similarly no way to manually mark a job as skipped, which is a bit misleading
• the new e2e-tests-composite-result job aggregates all of the results as a workaround
  • see https://github.com/orgs/community/discussions/9141#discussioncomment-2296809 and https://github.com/orgs/community/discussions/26822#discussioncomment-3305794
  • once this PR is merged, the required status checks on branch protection need to be changed
    • individual E2E test checks removed, composite check required now
    • note that this will also require that PRs opened earlier than this PR be rebased on top of this to get the new check so that they can pass CI

Verification

This is the PR in my own fork that I am using for testing purposes!

• Correctly only ran UI job
• Correctly ran UI + Lint
• Correctly only ran Lint
• Correctly only ran Codegen (this was cancelled early, but we only need to confirm that it ran)
• Correctly only ran E2E Tests (this was cancelled early, but we only need to confirm that it ran)
• Correctly ran Unit Tests, Lint, + E2E Tests (this was cancelled early, but we only need to confirm that it ran)
  • as Lint + E2E Tests will run whenever Unit Tests run too (since source files were changed)
• Correctly ran all jobs
• Confirmed that the new E2E composite check works correctly -- see all of the above

Notes to Reviewers

• See the "Changes to Status Checks" section above that we will need to implement
• We will also need to be a bit careful in making sure that any new code is properly listed in the files lists

Future Work

1. Further segment E2E tests -- not all tests necessarily need to run for all back-end changes
2. Add to other GH Workflows, like the Docs Workflow?
   • would not be a huge efficiency increase, but would limit some unnecessary runs
3. Add a check for argoexec-image job as well
   • this one may require some more effort to get everything necessary, particularly with repetition from .dockerignore etc

[agilgur5]

This was a testing PR; now that everything is confirmed working, I opened an upstream PR: argoproj#12006