Proposal: add new --sync-output flag to bake

.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

build/build.go

@@ -15,6 +15,7 @@ import (
 	"strconv"
 	"strings"
 	"sync"
+	"sync/atomic"
 	"syscall"
 	"time"
 
@@ -782,11 +783,11 @@ func Invoke(ctx context.Context, cfg ContainerConfig) error {
 	return err
 }
 
-func Build(ctx context.Context, drivers []DriverInfo, opt map[string]Options, docker DockerAPI, configDir string, w progress.Writer) (resp map[string]*client.SolveResponse, err error) {
-	return BuildWithResultHandler(ctx, drivers, opt, docker, configDir, w, nil, false)
+func Build(ctx context.Context, drivers []DriverInfo, opt map[string]Options, docker DockerAPI, configDir string, w progress.Writer, syncOutputs bool) (resp map[string]*client.SolveResponse, err error) {
+	return BuildWithResultHandler(ctx, drivers, opt, docker, configDir, w, nil, syncOutputs, false)
 }
 
-func BuildWithResultHandler(ctx context.Context, drivers []DriverInfo, opt map[string]Options, docker DockerAPI, configDir string, w progress.Writer, resultHandleFunc func(driverIndex int, rCtx *ResultContext), allowNoOutput bool) (resp map[string]*client.SolveResponse, err error) {
+func BuildWithResultHandler(ctx context.Context, drivers []DriverInfo, opt map[string]Options, docker DockerAPI, configDir string, w progress.Writer, resultHandleFunc func(driverIndex int, rCtx *ResultContext), syncOutputs bool, allowNoOutput bool) (resp map[string]*client.SolveResponse, err error) {
 	if len(drivers) == 0 {
 		return nil, errors.Errorf("driver required for build")
 	}
@@ -854,9 +855,11 @@ func BuildWithResultHandler(ctx context.Context, drivers []DriverInfo, opt map[s
 		}
 	}
 
+	msize := 0
 	for k, opt := range opt {
 		multiDriver := len(m[k]) > 1
 		hasMobyDriver := false
+		msize += len(m[k])
 		for i, dp := range m[k] {
 			di := drivers[dp.driverIndex]
 			if di.Driver.IsMobyDriver() {
@@ -928,6 +931,10 @@ func BuildWithResultHandler(ctx context.Context, drivers []DriverInfo, opt map[s
 
 	multiTarget := len(opt) > 1
 
+	buildGrp := &sync.WaitGroup{}
+	buildGrp.Add(msize)
+	errCount := int64(0)
+
 	for k, opt := range opt {
 		err := func(k string) error {
 			opt := opt
@@ -1147,6 +1154,8 @@ func BuildWithResultHandler(ctx context.Context, drivers []DriverInfo, opt map[s
 								res, err := c.Solve(ctx, req)
 								if err != nil {
 									if origErr != nil {
+										atomic.AddInt64(&errCount, 1)
+										buildGrp.Done()
 										return nil, err
 									}
 									var reqErr *errdefs.UnsupportedSubrequestError
@@ -1158,6 +1167,8 @@ func BuildWithResultHandler(ctx context.Context, drivers []DriverInfo, opt map[s
 												origErr = err
 												continue
 											}
+											atomic.AddInt64(&errCount, 1)
+											buildGrp.Done()
 											return nil, err
 										}
 										// buildkit v0.8 vendored in Docker 20.10 does not support typed errors
@@ -1167,6 +1178,8 @@ func BuildWithResultHandler(ctx context.Context, drivers []DriverInfo, opt map[s
 											continue
 										}
 									}
+									atomic.AddInt64(&errCount, 1)
+									buildGrp.Done()
 									return nil, err
 								}
 								if opt.PrintFunc != nil {
@@ -1176,6 +1189,27 @@ func BuildWithResultHandler(ctx context.Context, drivers []DriverInfo, opt map[s
 								if resultHandleFunc != nil {
 									resultHandleFunc(dp.driverIndex, &ResultContext{cc, res})
 								}
+
+								if syncOutputs {
+									err := res.EachRef(func(ref gateway.Reference) error {
+										return ref.Evaluate(ctx)
+									})
+									if err != nil {
+										atomic.AddInt64(&errCount, 1)
+										buildGrp.Done()
+										return nil, err
+									}
+								}
+								buildGrp.Done()
+								if syncOutputs {
+									buildGrp.Wait()
+									if atomic.LoadInt64(&errCount) > 0 {
+										// wait until cancelled
+										<-ctx.Done()
+										return nil, ctx.Err()
+									}
+								}
+
 								return res, nil
 							}
 						}, ch)

commands/bake.go

@@ -19,9 +19,10 @@ import (
 )
 
 type bakeOptions struct {
-	files     []string
-	overrides []string
-	printOnly bool
+	files      []string
+	overrides  []string
+	printOnly  bool
+	syncOutput bool
 	commonOptions
 }
 
@@ -146,7 +147,7 @@ func runBake(dockerCli command.Cli, targets []string, in bakeOptions) (err error
 		return nil
 	}
 
-	resp, err := build.Build(ctx, dis, bo, dockerAPI(dockerCli), confutil.ConfigDir(dockerCli), printer)
+	resp, err := build.Build(ctx, dis, bo, dockerAPI(dockerCli), confutil.ConfigDir(dockerCli), printer, in.syncOutput)
 	if err != nil {
 		return wrapBuildError(err, true)
 	}
@@ -190,6 +191,7 @@ func bakeCmd(dockerCli command.Cli, rootOpts *rootOptions) *cobra.Command {
 	flags.BoolVar(&options.exportLoad, "load", false, `Shorthand for "--set=*.output=type=docker"`)
 	flags.BoolVar(&options.printOnly, "print", false, "Print the options without building")
 	flags.BoolVar(&options.exportPush, "push", false, `Shorthand for "--set=*.output=type=registry"`)
+	flags.BoolVar(&options.syncOutput, "sync-output", false, "Ensure all builds complete before beginning output")
 	flags.StringArrayVar(&options.overrides, "set", nil, `Override target value (e.g., "targetpattern.key=value")`)
 
 	commonBuildFlags(&options.commonOptions, flags)

commands/build.go

@@ -297,7 +297,7 @@ func buildTargets(ctx context.Context, dockerCli command.Cli, opts map[string]bu
 		if res == nil || driverIndex < idx {
 			idx, res = driverIndex, gotRes
 		}
-	}, allowNoOutput)
+	}, false, allowNoOutput)
 	err1 := printer.Wait()
 	if err == nil {
 		err = err1

docs/reference/buildx_bake.md

@@ -25,6 +25,7 @@ Build from a file
 | [`--pull`](#pull) |  |  | Always attempt to pull all referenced images |
 | `--push` |  |  | Shorthand for `--set=*.output=type=registry` |
 | [`--set`](#set) | `stringArray` |  | Override target value (e.g., `targetpattern.key=value`) |
+| `--sync-output` |  |  | Ensure all builds complete before beginning output |
 
 
 <!---MARKER_GEN_END-->

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