CI: test build LuCI packages

While all LuCI packages should always build fine, this allows others to
directly install those packages within test setups.

Signed-off-by: Paul Spooren <mail@aparcar.org>

.github/workflows/build.yml

@@ -0,0 +1,71 @@
+name: Test Build
+
+on:
+  pull_request:
+
+jobs:
+  build:
+    name: Test ${{ matrix.arch }}
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        include:
+          - arch: x86_64
+            target: x86-64
+
+    steps:
+      - uses: actions/checkout@v2
+        with:
+          fetch-depth: 0
+
+      - name: Determine branch name
+        run: |
+          BRANCH="${GITHUB_BASE_REF#refs/heads/}"
+          echo "Building for $BRANCH"
+          echo "BRANCH=$BRANCH" >> $GITHUB_ENV
+
+      - name: Determine changed packages
+        run: |
+          # only detect packages with changes
+          PKG_ROOTS=$(find . -name Makefile | \
+            grep -v ".*/src/Makefile" | \
+            sed -e 's@./\(.*\)/Makefile@\1/@')
+          CHANGES=$(git diff --diff-filter=d --name-only origin/$BRANCH)
+
+          for ROOT in $PKG_ROOTS; do
+            for CHANGE in $CHANGES; do
+              if [[ "$CHANGE" == "$ROOT"* ]]; then
+                PACKAGES+=$(echo "$ROOT" | sed -e 's@.*/\(.*\)/@\1 @')
+                break
+              fi
+            done
+          done
+
+          # fallback to test packages if nothing explicitly changes this is
+          # should run if other mechanics in packages.git changed
+          PACKAGES="${PACKAGES:-luci-app-attendedsysupgrade}"
+
+          echo "Building $PACKAGES"
+          echo "PACKAGES=$PACKAGES" >> $GITHUB_ENV
+
+      - name: Build
+        uses: openwrt/gh-action-sdk@v3
+        env:
+          ARCH: ${{ matrix.arch }}-${{ env.BRANCH }}
+          FEEDNAME: packages_ci
+
+      - name: Move created packages to project dir
+        run: cp bin/packages/${{ matrix.arch }}/packages_ci/*.ipk . || true
+
+      - name: Store packages
+        uses: actions/upload-artifact@v2
+        with:
+          name: ${{ matrix.arch}}-packages
+          path: "*.ipk"
+
+      - name: Store logs
+        uses: actions/upload-artifact@v2
+        with:
+          name: ${{ matrix.arch}}-logs
+          path: logs/