add .travis.yml to run `make download check` on every package

Travis will run the following steps for every new or modified package:

- mkdir tempdir
- unpack SDK
- make download
- make check

make download will download the source code.
make check will do certain checks. Atm only checking the validity of
PKG_HASH.

Signed-off-by: Alexander Couzens <lynxis@fe80.eu>

.travis.yml

@@ -0,0 +1,12 @@
+language: c
+dist: trusty
+sudo: false
+cache:
+  directories:
+    - $HOME/sdk
+
+before_script:
+  - ./.travis_do.sh download_sdk
+
+script:
+  - ./.travis_do.sh test_packages

.travis_do.sh

@@ -0,0 +1,108 @@
+#!/bin/sh
+#
+# MIT Alexander Couzens <lynxis@fe80.eu>
+
+set -e
+
+SDK_HOME="$HOME/sdk"
+SDK_PATH=https://downloads.lede-project.org/snapshots/targets/ar71xx/generic/
+SDK=lede-sdk-ar71xx-generic_gcc-5.4.0_musl.Linux-x86_64
+PACKAGES_DIR="$PWD"
+
+# download will run on the `before_script` step
+# The travis cache will be used (all files under $HOME/sdk/). Meaning
+# We don't have to download the file again
+download_sdk() {
+	mkdir -p "$SDK_HOME"
+	cd "$SDK_HOME"
+
+	echo "=== download SDK"
+	wget "$SDK_PATH/sha256sums" -O sha256sums
+	wget "$SDK_PATH/sha256sums.gpg" -O sha256sums.asc
+
+	# LEDE Build System (LEDE GnuPG key for unattended build jobs)
+	gpg --recv 0xCD84BCED626471F1
+	# LEDE Release Builder (17.01 "Reboot" Signing Key)
+	gpg --recv 0x833C6010D52BBB6B
+	gpg --verify sha256sums.asc
+	grep "$SDK" sha256sums > sha256sums.small
+
+	# if missing, outdated or invalid, download again
+	if ! sha256sum -c ./sha256sums.small ; then
+		wget "$SDK_PATH/$SDK.tar.xz" -O "$SDK.tar.xz"
+	fi
+
+	# check again and fail here if the file is still bad
+	sha256sum -c ./sha256sums.small
+	echo "=== SDK is up-to-date"
+}
+
+# test_package will run on the `script` step.
+# test_package call make download check for very new/modified package in it's
+# own clean sdk directory
+test_packages() {
+	# search for new or modified packages. PKGS will hold a list of package like 'admin/muninlite admin/monit ...'
+	PKGS=$(git diff --stat "$TRAVIS_COMMIT_RANGE" | grep Makefile | grep -v '/files/' | awk '{ print $1}' | awk -F'/Makefile' '{ print $1 }')
+
+	if [ -z "$PKGS" ] ; then
+		echo "No new or modified packages found!" >&2
+		exit 0
+	fi
+
+	echo "=== Found new/modified packages:"
+	for pkg in $PKGS ; do
+		echo "===+ $pkg"
+	done
+
+	# E.g: pkg_dir => admin/muninlite
+	#      pkg_name => muninlite
+	for pkg_dir in $PKGS ; do
+		pkg_name=$(echo "$pkg_dir" | awk -F/ '{ print $NF }')
+		tmp_path=$HOME/tmp/$pkg_name/
+
+		echo "=== $pkg_name Testing package"
+
+		# create a clean sdk for every package
+		mkdir -p "$tmp_path"
+		cd "$tmp_path"
+		tar Jxf "$SDK_HOME/$SDK.tar.xz"
+		cd "$SDK"
+
+		cat > feeds.conf <<EOF
+src-git base https://git.lede-project.org/source.git
+src-link packages $PACKAGES_DIR
+src-git luci https://git.lede-project.org/project/luci.git
+src-git routing https://git.lede-project.org/feed/routing.git
+src-git telephony https://git.lede-project.org/feed/telephony.git
+EOF
+		./scripts/feeds update 2>/dev/null >/dev/null
+		./scripts/feeds install "$pkg_name"
+
+		make defconfig
+		make "package/$pkg_name/download" V=s
+		make "package/$pkg_name/check" V=s | tee -a logoutput
+		grep WARNING logoutput && exit 1
+		rm -rf "$tmp_path"
+		echo "=== $pkg_name Finished package"
+	done
+}
+
+export
+
+if [ "$TRAVIS_PULL_REQUEST" = false ] ; then
+	echo "Only Pull Requests are supported at the moment." >&2
+	exit 0
+fi
+
+
+if [ $# -ne 1 ] ; then
+	cat <<EOF
+Usage: $0 (download_sdk|test_packages)
+
+download_sdk - download the SDK to $HOME/sdk.tar.xz
+test_packages - do a make check on the package
+EOF
+	exit 1
+fi
+
+$@