tools: add script to lint commit messages

This script attempts to guess the target upstream branch.
To manually specify, e.g. to target `canary-base`:
  TARGET_BRANCH=canary-base bash lint-commit-message.sh

tools/lint-commit-message.sh

@@ -0,0 +1,41 @@
+#!/usr/bin/env bash
+
+# Shell script to lint commit messages
+#
+# Depends on git, node, npm and npx being in $PATH.
+#
+# This script must be be in the tools directory when it runs because it uses
+# $BASH_SOURCE[0] to determine directories to work in.
+#
+# This script attempts to guess the target upstream branch. To manually specify:
+# e.g. to target `canary-base`:
+# TARGET_BRANCH=canary-base bash lint-commit-message.sh
+
+ROOT_DIR="$( dirname "${BASH_SOURCE[0]}" )/.."
+
+# Work out what branch is being targetted
+MAJOR_VERSION=$( grep '#define NODE_MAJOR_VERSION [0-9][0-9]*' "${ROOT_DIR}/src/node_version.h" | awk '{print $(NF)}' )
+MINOR_VERSION=$( grep '#define NODE_MINOR_VERSION [0-9][0-9]*' "${ROOT_DIR}/src/node_version.h" | awk '{print $(NF)}' )
+PATCH_VERSION=$( grep '#define NODE_PATCH_VERSION [0-9][0-9]*' "${ROOT_DIR}/src/node_version.h" | awk '{print $(NF)}' )
+# If the version is not in the CHANGELOG assume the target branch is master
+if grep -q "${MAJOR_VERSION}\.${MINOR_VERSION}\.${PATCH_VERSION}" "${ROOT_DIR}/CHANGELOG.md"; then
+  TARGET_BRANCH=${TARGET_BRANCH:-"v${MAJOR_VERSION}.x-staging"}
+else
+  TARGET_BRANCH=${TARGET_BRANCH:-"master"}
+fi
+echo "Target branch is ${TARGET_BRANCH}"
+
+# Make sure we're up to date
+UPSTREAM=$( git remote -v | grep "github\.com.*nodejs/node.* (fetch)" | awk '{print $(1)}' )
+echo "Fetching upstream remote ${UPSTREAM}"
+git fetch "${UPSTREAM}" "${TARGET_BRANCH}":"${TARGET_BRANCH}"
+COMMON_ANCESTOR=$( git merge-base "${UPSTREAM}/$TARGET_BRANCH" HEAD )
+FIRST_COMMIT=$( git rev-list --no-merges ${COMMON_ANCESTOR}..HEAD | tail -1 )
+
+if [ -n "${FIRST_COMMIT}" ]; then
+  echo "Linting the first commit message according to the guidelines at https://goo.gl/p2fr5Q"
+  echo "$( git log -1 ${FIRST_COMMIT} )"
+  echo "${FIRST_COMMIT}" | xargs npx -q core-validate-commit --no-validate-metadata
+else
+  echo "No commits found to lint"
+fi