dockerfile: fix onbuild propagation for child stages

frontend/dockerfile/dockerfile2llb/convert.go

@@ -1065,6 +1065,8 @@ func (ds *dispatchState) init() {
 	ds.state = ds.base.state
 	ds.platform = ds.base.platform
 	ds.image = clone(ds.base.image)
+	// onbuild triggers to not carry over from base stage
+	ds.image.Config.OnBuild = nil
 	ds.baseImg = cloneX(ds.base.baseImg)
 	// Utilize the same path index as our base image so we propagate
 	// the paths we use back to the base image.

frontend/dockerfile/dockerfile2llb/image.go

@@ -12,6 +12,7 @@ func clone(src dockerspec.DockerOCIImage) dockerspec.DockerOCIImage {
 	img.Config.Env = append([]string{}, src.Config.Env...)
 	img.Config.Cmd = append([]string{}, src.Config.Cmd...)
 	img.Config.Entrypoint = append([]string{}, src.Config.Entrypoint...)
+	img.Config.OnBuild = append([]string{}, src.Config.OnBuild...)
 	return img
 }
 

frontend/dockerfile/dockerfile_test.go

@@ -127,6 +127,7 @@ var allTests = integration.TestFuncs(
 	testEnvEmptyFormatting,
 	testCacheMultiPlatformImportExport,
 	testOnBuildCleared,
+	testOnBuildWithChildStage,
 	testOnBuildInheritedStageRun,
 	testOnBuildInheritedStageWithFrom,
 	testOnBuildNewDeps,
@@ -5013,6 +5014,96 @@ ONBUILD RUN mkdir \out && echo 11>> \out\foo
 	require.Equal(t, integration.UnixOrWindows("11", "11\r\n"), string(dt))
 }
 
+// testOnBuildWithChildStage tests that ONBUILD rules from the parent image do
+// not run again if another stage inherits from current stage.
+// moby/buildkit#5578
+func testOnBuildWithChildStage(t *testing.T, sb integration.Sandbox) {
+	integration.SkipOnPlatform(t, "windows")
+	workers.CheckFeatureCompat(t, sb, workers.FeatureDirectPush)
+	f := getFrontend(t, sb)
+
+	registry, err := sb.NewRegistry()
+	if errors.Is(err, integration.ErrRequirements) {
+		t.Skip(err.Error())
+	}
+	require.NoError(t, err)
+
+	dockerfile := []byte(`
+FROM busybox
+ONBUILD RUN mkdir -p /out && echo -n yes >> /out/didrun
+`)
+
+	dir := integration.Tmpdir(
+		t,
+		fstest.CreateFile("Dockerfile", dockerfile, 0600),
+	)
+
+	c, err := client.New(sb.Context(), sb.Address())
+	require.NoError(t, err)
+	defer c.Close()
+
+	target := registry + "/buildkit/testonbuildstage:base"
+
+	_, err = f.Solve(sb.Context(), c, client.SolveOpt{
+		Exports: []client.ExportEntry{
+			{
+				Type: client.ExporterImage,
+				Attrs: map[string]string{
+					"push": "true",
+					"name": target,
+				},
+			},
+		},
+		LocalMounts: map[string]fsutil.FS{
+			dockerui.DefaultLocalNameDockerfile: dir,
+			dockerui.DefaultLocalNameContext:    dir,
+		},
+	}, nil)
+	require.NoError(t, err)
+
+	dockerfile = []byte(fmt.Sprintf(`
+FROM %s AS base
+RUN [ -f /out/didrun ] && touch /step1
+RUN rm /out/didrun
+RUN [ ! -f /out/didrun ] && touch /step2
+
+FROM base AS child
+RUN [ ! -f /out/didrun ] && touch /step3
+
+FROM scratch
+COPY --from=child /step* /
+	`, target))
+
+	dir = integration.Tmpdir(
+		t,
+		fstest.CreateFile("Dockerfile", dockerfile, 0600),
+	)
+	destDir := t.TempDir()
+
+	_, err = f.Solve(sb.Context(), c, client.SolveOpt{
+		Exports: []client.ExportEntry{
+			{
+				Type:      client.ExporterLocal,
+				OutputDir: destDir,
+			},
+		},
+		LocalMounts: map[string]fsutil.FS{
+			dockerui.DefaultLocalNameDockerfile: dir,
+			dockerui.DefaultLocalNameContext:    dir,
+		},
+	}, nil)
+	require.NoError(t, err)
+
+	_, err = os.Stat(filepath.Join(destDir, "step1"))
+	require.NoError(t, err)
+
+	_, err = os.Stat(filepath.Join(destDir, "step2"))
+	require.NoError(t, err)
+
+	_, err = os.Stat(filepath.Join(destDir, "step3"))
+	require.NoError(t, err)
+}
+
 func testOnBuildNamedContext(t *testing.T, sb integration.Sandbox) {
 	integration.SkipOnPlatform(t, "windows")
 	workers.CheckFeatureCompat(t, sb, workers.FeatureOCIExporter, workers.FeatureOCILayout)