build: add --annotation shortcut flag

This extracts the same logic for parsing annotations from the imagetools
create command, and allows the same flags to be attached to the build
command.

These annotations are then merged into all provided exporters.

Signed-off-by: Justin Chadwell <me@jedevc.com>

tests/build.go

@@ -20,6 +20,7 @@ import (
 	"github.com/moby/buildkit/util/testutil/integration"
 	"github.com/opencontainers/go-digest"
 	"github.com/pkg/errors"
+	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 )
 
@@ -40,6 +41,7 @@ var buildTests = []func(t *testing.T, sb integration.Sandbox){
 	testBuildMobyFromLocalImage,
 	testBuildDetailsLink,
 	testBuildProgress,
+	testBuildAnnotations,
 }
 
 func testBuild(t *testing.T, sb integration.Sandbox) {
@@ -313,3 +315,46 @@ func testBuildProgress(t *testing.T, sb integration.Sandbox) {
 	require.Contains(t, string(plainOutput), "[internal] load build definition from Dockerfile")
 	require.Contains(t, string(plainOutput), "[base 1/3] FROM docker.io/library/busybox:latest")
 }
+
+func testBuildAnnotations(t *testing.T, sb integration.Sandbox) {
+	if sb.Name() == "docker" {
+		t.Skip("annotations not supported on docker worker")
+	}
+
+	dir := createTestProject(t)
+
+	registry, err := sb.NewRegistry()
+	if errors.Is(err, integration.ErrRequirements) {
+		t.Skip(err.Error())
+	}
+	require.NoError(t, err)
+	target := registry + "/buildx/registry:latest"
+
+	annotations := []string{
+		"--annotation", "example1=www",
+		"--annotation", "index:example2=xxx",
+		"--annotation", "manifest:example3=yyy",
+		"--annotation", "manifest-descriptor[" + platforms.DefaultString() + "]:example4=zzz",
+	}
+	out, err := buildCmd(sb, withArgs(annotations...), withArgs(fmt.Sprintf("--output=type=image,name=%s,push=true", target), dir))
+	require.NoError(t, err, string(out))
+
+	desc, provider, err := contentutil.ProviderFromRef(target)
+	require.NoError(t, err)
+	imgs, err := testutil.ReadImages(sb.Context(), provider, desc)
+	require.NoError(t, err)
+
+	pk := platforms.Format(platforms.Normalize(platforms.DefaultSpec()))
+	img := imgs.Find(pk)
+	require.NotNil(t, img)
+
+	require.NotNil(t, imgs.Index)
+	assert.Equal(t, "xxx", imgs.Index.Annotations["example2"])
+
+	require.NotNil(t, img.Manifest)
+	assert.Equal(t, "www", img.Manifest.Annotations["example1"])
+	assert.Equal(t, "yyy", img.Manifest.Annotations["example3"])
+
+	require.NotNil(t, img.Desc)
+	assert.Equal(t, "zzz", img.Desc.Annotations["example4"])
+}