krel: Merge any commits in the remote branch before push

[puerco]

What type of PR is this?

/kind feature

What this PR does / why we need it:

To prevent divergent branches, we now fetch the remote and merge any commits found at the origin before pushing release branches.

Signed-off-by: Adolfo García Veytia (Puerco) [email protected]

Which issue(s) this PR fixes:

Special notes for your reviewer:

Please take a good look at the change and if you think of a way to test it in gcb lets do it.

When running on release, krel will merge the commits from the remote branch if it finds any. It will create a merge commit. The image below is from my local test with the code of the PR in this branch:

https://github.com/puerco/lab/commits/release-1.16

The following graph shows the result. The commits at the top were made in github directly, those on the bottom on my local machine:

The code to test it:

package main

import (
	"github.com/sirupsen/logrus"
	"k8s.io/release/pkg/release"
)

func main() {
	pusher, err := release.NewGitPusher(&release.GitObjectPusherOptions{
		DryRun:     false,
		MaxRetries: 0,
		RepoPath:   "/path/to/repo",
	})
	if err != nil {
		logrus.Fatal(err)
	}
	if err := pusher.PushBranch("release-1.16"); err != nil {
		logrus.Fatal(err)
	}
	logrus.Info("Pushed")
}

/assign @saschagrunert @xmudrii
/priority critical-urgent
/milestone v1.22
/cc @kubernetes/release-engineering

Does this PR introduce a user-facing change?

When running release from a non-main branch, krel will now merge any commits before pushing the branch back to github, avoiding conflicts due to divergent branches. 

[saschagrunert]

Testing manually for the latest 1.19 staged sources:

> export TOOL_ORG=puerco TOOL_REF=merge-unexpected-commits && \
    go run ./cmd/krel release --type=official --branch=release-1.19 \
        --build-version=v1.19.12-rc.0.48+5dd397c4514b63

https://console.cloud.google.com/cloud-build/builds/c2cc13dd-28ac-4557-80c2-479d7f9d28a5?project=648026197307

[saschagrunert]

Looking good:

Step #3: INFO[2021-06-17T07:49:55Z] Verifying release-1.19 branch exists in the repo 
Step #3: INFO[2021-06-17T07:49:55Z] Branch release-1.19 found in the repository  
Step #3: INFO[2021-06-17T07:49:55Z] Checking out branch release-1.19 to merge upstream changes 
Step #3: INFO[2021-06-17T07:49:56Z] Fetching origin                              
Step #3: INFO[2021-06-17T07:50:00Z] Merging origin/release-1.19                    

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: puerco, saschagrunert, xmudrii

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• pkg/OWNERS [puerco,saschagrunert,xmudrii]

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