FirstParent returns the first parent of a commit.

FirstParentList visits the ancestors of c using the FirstParent func.

MergePoints creates a look-up table from feature branch commit hashes to their merge commits onto the given mainline.

SourceCommitToDstCommits returns a mapping from all kube mainline commits to the corresponding dst commits after collapsing using "git filter-branch --sub-directory-filter": dst upstream | | F'<--F z | y | E'<--E x ,D | / | C'<--C w | v<-, | |-B `A - initial commit.

SourceHash extracts kube commit from commit message The baseRepoName default to "kubernetes".