add script to check if changes to vendor are valid

Signed-off-by: Jess Frazelle <acidburn@google.com>

.travis.yml

@@ -20,3 +20,4 @@
     - go test $(go list ./... | grep -v vendor)
     - go build ./hack/licenseok
     - find . -path ./vendor -prune -o -type f -name "*.go" -printf '%P\n' | xargs ./licenseok
+    - ./hack/validate-vendor.bash

hack/validate-vendor.bash

@@ -0,0 +1,48 @@
+#!/bin/bash
+# Copyright 2017 The Go Authors. All rights reserved.
+# Use of this source code is governed by a BSD-style
+# license that can be found in the LICENSE file.
+#
+# This script checks if we changed anything with regard to dependency management
+# for our repo and makes sure that it was done in a valid way.
+
+set -e -o pipefail
+
+# TRAVIS_BRANCH is the name of the branch targeted by the pull request.
+# but we won't have that set if running locally
+if [ -z "$TRAVIS_BRANCH" ]; then
+	VALIDATE_REPO='git@github.com:golang/nest.git'
+	VALIDATE_BRANCH='master'
+
+	git fetch -q "$VALIDATE_REPO" "refs/heads/$VALIDATE_BRANCH"
+	TRAVIS_BRANCH="$(git rev-parse --verify FETCH_HEAD)"
+fi
+
+VALIDATE_HEAD="$(git rev-parse --verify HEAD)"
+
+IFS=$'\n'
+files=( $(git diff "$TRAVIS_BRANCH...$VALIDATE_HEAD" --diff-filter=ACMR --name-only -- 'manifest.json' 'lock.json' 'vendor/' || true) )
+unset IFS
+
+if [ ${#files[@]} -gt 0 ]; then
+	# We run ensure to and see if we have a diff afterwards
+	go build
+	./dep ensure
+	# Let see if the working directory is clean
+	diffs="$(git status --porcelain -- vendor manifest.json lock.json 2>/dev/null)"
+	if [ "$diffs" ]; then
+		{
+			echo 'The result of ensure differs'
+			echo
+			echo "$diffs"
+			echo
+			echo 'Please vendor your package with github.com/golang/nest.'
+			echo
+		} >&2
+		false
+	else
+		echo 'Congratulations! All vendoring changes are done the right way.'
+	fi
+else
+    echo 'No vendor changes in diff.'
+fi