bake(e2e): simple test for sync-output flag

Signed-off-by: CrazyMax <crazy-max@users.noreply.github.com>

.github/workflows/e2e.yml

@@ -168,3 +168,36 @@ jobs:
           DRIVER_OPT: ${{ matrix.driver-opt }}
           ENDPOINT: ${{ matrix.endpoint }}
           PLATFORMS: ${{ matrix.platforms }}
+
+  cases:
+    runs-on: ubuntu-20.04
+    needs:
+      - build
+    strategy:
+      fail-fast: false
+      matrix:
+        case:
+          - bake-sync-output
+    steps:
+      -
+        name: Checkout
+        uses: actions/checkout@v3
+      -
+        name: Install buildx
+        uses: actions/download-artifact@v3
+        with:
+          name: binary
+          path: /home/runner/.docker/cli-plugins
+      -
+        name: Fix perms and check
+        run: |
+          chmod +x /home/runner/.docker/cli-plugins/docker-buildx
+          docker buildx version
+      -
+        name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v2
+      -
+        name: Test
+        working-directory: ./test/${{ matrix.case }}
+        run: |
+          ./test.sh

test/bake-sync-output/.gitignore

@@ -0,0 +1 @@
+/out

test/bake-sync-output/bar.Dockerfile

@@ -0,0 +1,5 @@
+FROM busybox
+RUN echo bar > /bar
+
+FROM scratch
+COPY --from=0 /bar /bar

test/bake-sync-output/docker-bake.hcl

@@ -0,0 +1,13 @@
+group "default" {
+  targets = ["foo", "bar"]
+}
+
+target "foo" {
+  dockerfile = "foo.Dockerfile"
+  output = ["out"]
+}
+
+target "bar" {
+  dockerfile = "bar.Dockerfile"
+  output = ["out"]
+}

test/bake-sync-output/foo.Dockerfile

@@ -0,0 +1,5 @@
+FROM busybox
+RUN echo foo > /foo
+
+FROM scratch
+COPY --from=0 /foo /foo

test/bake-sync-output/test.sh

@@ -0,0 +1,13 @@
+#!/usr/bin/env bash
+
+set -ex
+
+rm -rf ./out
+
+docker buildx bake --print
+docker buildx bake --sync-output
+
+if [[ ! -f ./out/foo || ! -f ./out/bar ]]; then
+  echo >&2 "error: missing output files"
+  exit 1
+fi