Add mirror-upstream-branches.sh script (knative#1134)

* Add mirror-upstream-branches.sh script

* Fix multiple release branches

* Fix commented code

openshift/release/mirror-upstream-branches.sh

@@ -0,0 +1,41 @@
+#!/usr/bin/env bash
+
+# Usage: openshift/release/mirror-upstream-branches.sh
+# This should be run from the basedir of the repo with no arguments
+
+
+set -ex
+readonly TMPDIR=$(mktemp -d knativeClientBranchingCheckXXXX -p /tmp/)
+
+git fetch upstream --tags
+git fetch openshift --tags
+
+# We need to seed this with a few releases that, otherwise, would make
+# the processing regex less clear with more anomalies
+cat >> "$TMPDIR"/midstream_branches <<EOF
+0.2
+0.3
+EOF
+
+git branch --list -a "upstream/release-1.*" | cut -f3 -d'/' | cut -f2 -d'-' > "$TMPDIR"/upstream_branches
+git branch --list -a "openshift/release-v1.*" | cut -f3 -d'/' | cut -f2 -d'v' | cut -f1,2 -d'.' >> "$TMPDIR"/midstream_branches
+
+sort -o "$TMPDIR"/midstream_branches "$TMPDIR"/midstream_branches
+sort -o "$TMPDIR"/upstream_branches "$TMPDIR"/upstream_branches
+comm -32 "$TMPDIR"/upstream_branches "$TMPDIR"/midstream_branches > "$TMPDIR"/new_branches
+
+UPSTREAM_BRANCHES=$(cat "$TMPDIR"/new_branches | tr '\n' ' ')
+
+if [ -z "$UPSTREAM_BRANCHES" ]; then
+    echo "no new branch, exiting"
+    exit 0
+fi
+
+for UPSTREAM_BRANCH in ${UPSTREAM_BRANCHES[@]}; do
+  echo "found upstream branch: $UPSTREAM_BRANCH"
+  UPSTREAM_TAG="knative-v$UPSTREAM_BRANCH.0"
+  MIDSTREAM_BRANCH="release-v$UPSTREAM_BRANCH"
+  $(dirname "${BASH_SOURCE[0]}")/openshift/release/create-release-branch.sh "$UPSTREAM_TAG" "$MIDSTREAM_BRANCH"
+  # we would check the error code, but we 'set -e', so assume we're fine
+  git push openshift "$MIDSTREAM_BRANCH"
+done

openshift/release/update-to-head.sh

@@ -20,6 +20,9 @@
 set -e
 REPO_NAME=$(basename $(git rev-parse --show-toplevel))
 
+# Check if there's an upstream release we need to mirror downstream
+openshift/release/mirror-upstream-branches.sh
+
 # Custom files
 custom_files=$(cat <<EOT | tr '\n' ' '
 openshift