Automatically determine remote upstream name.

Also add option to force Godeps verification checks on post-commit
Jenkins.

hack/lib/util.sh

@@ -312,4 +312,33 @@ kube::util::gv-to-swagger-name() {
   esac
 }
 
+# Returns the name of the upstream remote repository name for the local git
+# repo, e.g. "upstream" or "origin".
+kube::util::git_upstream_remote_name() {
+  git remote -v | grep fetch |\
+    grep -E 'github.com/kubernetes/kubernetes|k8s.io/kubernetes' |\
+    head -n 1 | awk '{print $1}'
+}
+
+# Checks whether there are any files matching pattern $2 changed between the
+# current branch and upstream branch named by $1.
+# Returns 1 (false) if there are no changes, 0 (true) if there are changes
+# detected.
+kube::util::has_changes_against_upstream_branch() {
+  local -r git_branch=$1
+  local -r pattern=$2
+
+  readonly full_branch="$(kube::util::git_upstream_remote_name)/${git_branch}"
+  echo "Checking for '${pattern}' changes against '${full_branch}'"
+  # make sure the branch is valid, otherwise the check will pass erroneously.
+  if ! git describe "${full_branch}" >/dev/null; then
+    exit 1
+  fi
+  # notice this uses ... to find the first shared ancestor
+  if ! git diff --name-only "${full_branch}...HEAD" | grep "${pattern}" > /dev/null; then
+    echo "No '${pattern}' changes detected."
+    return 1
+  fi
+}
+
 # ex: ts=2 sw=2 et filetype=sh