Proposal: Merge PR branch onto master in Jenkins checkout phrase

[cofyc]

checkout([$class: 'GitSCM', branches: [[name: "${BUILD_BRANCH}"]], userRemoteConfigs:[[url: "${BUILD_URL}", credentialsId: "${CREDENTIALS_ID}"]]])

->

checkout([$class: 'GitSCM', branches: [[name: "${BUILD_BRANCH}"]], userRemoteConfigs:[[url: "${BUILD_URL}", credentialsId: "${CREDENTIALS_ID}"]], mergeRemote: 'origin', mergeTarget: 'master', fastForwardMode: 'NO_FF'])

xref: https://jenkins.io/doc/pipeline/steps/workflow-scm-step/

Currently, CI job checkouts PR branch to test, but the PR branch may be out of date.

It's best and convenient to merge the PR branch onto master before running the CI job. And it helps when the broken master is fixed, blocked PRs are not needed to be rebased onto the new master. (example #392 (comment))

[cofyc]

cc @tennix @weekface

[weekface]

I am fine with it @onlymellb PTAL

[cofyc]

Another way is to enable "Require branches to be up to date before merging" in github repo settings.

[cofyc]

@weekface It seems that we have "Require branches to be up to date before merging" enabled?

[weekface]

yes

[cofyc]

Then I think we can close this now.