build: support for named contexts(stages)

build/build.go

@@ -14,6 +14,7 @@ import (
 	"strconv"
 	"strings"
 	"sync"
+	"syscall"
 	"time"
 
 	"github.com/containerd/containerd/images"
@@ -79,6 +80,7 @@ type Inputs struct {
 	InStream         io.Reader
 	ContextState     *llb.State
 	DockerfileInline string
+	NamedContexts    map[string]string
 }
 
 type DriverInfo struct {
@@ -1080,6 +1082,27 @@ func LoadInputs(ctx context.Context, d driver.Driver, inp Inputs, pw progress.Wr
 
 	target.FrontendAttrs["filename"] = dockerfileName
 
+	for k, v := range inp.NamedContexts {
+		target.FrontendAttrs["frontend.caps"] = "moby.buildkit.frontend.contexts+forward"
+		if urlutil.IsGitURL(v) || urlutil.IsURL(v) || strings.HasPrefix(v, "docker-image://") {
+			target.FrontendAttrs["context:"+k] = v
+			continue
+		}
+		st, err := os.Stat(v)
+		if err != nil {
+			return nil, errors.Wrapf(err, "failed to get build context %v", k)
+		}
+		if !st.IsDir() {
+			return nil, errors.Wrapf(syscall.ENOTDIR, "failed to get build context path %v", v)
+		}
+		localName := k
+		if k == "context" || k == "dockerfile" {
+			localName = "_" + k // underscore to avoid collisions
+		}
+		target.LocalDirs[localName] = v
+		target.FrontendAttrs["context:"+k] = "local:" + localName
+	}
+
 	release := func() {
 		for _, dir := range toRemove {
 			os.RemoveAll(dir)

commands/build.go

@@ -20,17 +20,20 @@ import (
 	"github.com/docker/cli/cli"
 	"github.com/docker/cli/cli/command"
 	dockeropts "github.com/docker/cli/opts"
+	"github.com/docker/distribution/reference"
 	"github.com/docker/docker/pkg/ioutils"
 	"github.com/docker/go-units"
 	"github.com/moby/buildkit/client"
 	"github.com/moby/buildkit/session/auth/authprovider"
 	"github.com/moby/buildkit/solver/errdefs"
 	"github.com/moby/buildkit/util/appcontext"
+	"github.com/moby/buildkit/util/grpcerrors"
 	"github.com/morikuni/aec"
 	"github.com/pkg/errors"
 	"github.com/sirupsen/logrus"
 	"github.com/spf13/cobra"
 	"github.com/spf13/pflag"
+	"google.golang.org/grpc/codes"
 )
 
 const defaultTargetName = "default"
@@ -44,6 +47,7 @@ type buildOptions struct {
 	cacheFrom    []string
 	cacheTo      []string
 	cgroupParent string
+	contexts     []string
 	extraHosts   []string
 	imageIDFile  string
 	labels       []string
@@ -100,11 +104,17 @@ func runBuild(dockerCli command.Cli, in buildOptions) (err error) {
 		in.progress = "quiet"
 	}
 
+	contexts, err := parseContextNames(in.contexts)
+	if err != nil {
+		return err
+	}
+
 	opts := build.Options{
 		Inputs: build.Inputs{
 			ContextPath:    in.contextPath,
 			DockerfilePath: in.dockerfileName,
 			InStream:       os.Stdin,
+			NamedContexts:  contexts,
 		},
 		BuildArgs:   listToMap(in.buildArgs, true),
 		ExtraHosts:  in.extraHosts,
@@ -209,6 +219,7 @@ func runBuild(dockerCli command.Cli, in buildOptions) (err error) {
 	}
 
 	imageID, err := buildTargets(ctx, dockerCli, map[string]build.Options{defaultTargetName: opts}, in.progress, contextPathHash, in.builder, in.metadataFile)
+	err = wrapBuildError(err)
 	if err != nil {
 		return err
 	}
@@ -339,6 +350,8 @@ func buildCmd(dockerCli command.Cli, rootOpts *rootOptions) *cobra.Command {
 	flags.StringVar(&options.cgroupParent, "cgroup-parent", "", "Optional parent cgroup for the container")
 	flags.SetAnnotation("cgroup-parent", annotation.ExternalURL, []string{"https://docs.docker.com/engine/reference/commandline/build/#use-a-custom-parent-cgroup---cgroup-parent"})
 
+	flags.StringArrayVar(&options.contexts, "build-context", []string{}, "Additional build contexts (e.g., name=path)")
+
 	flags.StringVarP(&options.dockerfileName, "file", "f", "", `Name of the Dockerfile (default: "PATH/Dockerfile")`)
 	flags.SetAnnotation("file", annotation.ExternalURL, []string{"https://docs.docker.com/engine/reference/commandline/build/#specify-a-dockerfile--f"})
 
@@ -462,3 +475,49 @@ func listToMap(values []string, defaultEnv bool) map[string]string {
 	}
 	return result
 }
+
+func parseContextNames(values []string) (map[string]string, error) {
+	if len(values) == 0 {
+		return nil, nil
+	}
+	result := make(map[string]string, len(values))
+	for _, value := range values {
+		kv := strings.SplitN(value, "=", 2)
+		if len(kv) != 2 {
+			return nil, errors.Errorf("invalid context value: %s, expected key=value", value)
+		}
+		named, err := reference.ParseNormalizedNamed(kv[0])
+		if err != nil {
+			return nil, errors.Wrapf(err, "invalid context name %s", kv[0])
+		}
+		name := strings.TrimSuffix(reference.FamiliarString(named), ":latest")
+		result[name] = kv[1]
+	}
+	return result, nil
+}
+
+func wrapBuildError(err error) error {
+	if err == nil {
+		return nil
+	}
+	st, ok := grpcerrors.AsGRPCStatus(err)
+	if ok {
+		if st.Code() == codes.Unimplemented && strings.Contains(st.Message(), "unsupported frontend capability moby.buildkit.frontend.contexts") {
+			return &wrapped{err, "current frontend does not support --build-context. Named contexts are supported since Dockerfile v1.4"}
+		}
+	}
+	return err
+}
+
+type wrapped struct {
+	err error
+	msg string
+}
+
+func (w *wrapped) Error() string {
+	return w.msg
+}
+
+func (w *wrapped) Unwrap() error {
+	return w.err
+}

docs/reference/buildx_build.md

@@ -18,6 +18,7 @@ Start a build
 | [`--add-host stringSlice`](https://docs.docker.com/engine/reference/commandline/build/#add-entries-to-container-hosts-file---add-host) | Add a custom host-to-IP mapping (format: `host:ip`) |
 | [`--allow stringSlice`](#allow) | Allow extra privileged entitlement (e.g., `network.host`, `security.insecure`) |
 | [`--build-arg stringArray`](https://docs.docker.com/engine/reference/commandline/build/#set-build-time-variables---build-arg) | Set build-time variables |
+| [`--build-context stringArray`](#build-context) | Additional build contexts (e.g., name=path) |
 | [`--builder string`](#builder) | Override the configured builder instance |
 | [`--cache-from stringArray`](#cache-from) | External cache sources (e.g., `user/app:cache`, `type=local,src=path/to/dir`) |
 | [`--cache-to stringArray`](#cache-to) | Cache export destinations (e.g., `user/app:cache`, `type=local,dest=path/to/dir`) |
@@ -303,6 +304,39 @@ $ docker buildx build --cache-to=type=gha .
 
 More info about cache exporters and available attributes: https://github.com/moby/buildkit#export-cache
 
+
+### <a name="build-context"></a> Additional build contexts (--build-context)
+
+```
+--build-context=name=VALUE
+```
+
+Define additional build context with specified contents. In Dockerfile the context can be accessed when `FROM name` or `--from=name` is used.
+When Dockerfile defines a stage with the same name it is overwritten.
+
+The value can be a local source directory, container image (with docker-image:// prefix), Git or HTTP URL.
+
+**Examples**
+
+Replace `alpine:latest` with a pinned one:
+
+```console
+$ docker buildx build --build-context alpine=docker-image://alpine@sha256:0123456789 .
+```
+
+Expose a secondary local source directory:
+
+```console
+$ docker buildx build --build-context project=path/to/project/source .
+# docker buildx build --build-context project=https://github.com/myuser/project.git .
+```
+
+```Dockerfile
+FROM alpine
+COPY --from=project myfile /
+```
+
+
 ### <a name="allow"></a> Allow extra privileged entitlement (--allow)
 
 ```

go.mod

@@ -47,6 +47,7 @@ require (
 	go.opentelemetry.io/otel v1.2.0
 	go.opentelemetry.io/otel/trace v1.2.0
 	golang.org/x/sync v0.0.0-20210220032951-036812b2e83c
+	google.golang.org/grpc v1.42.0
 	gopkg.in/dancannon/gorethink.v3 v3.0.5 // indirect
 	gopkg.in/fatih/pool.v2 v2.0.0 // indirect
 	gopkg.in/gorethink/gorethink.v3 v3.0.5 // indirect

vendor/modules.txt

@@ -564,6 +564,7 @@ google.golang.org/genproto/googleapis/rpc/errdetails
 google.golang.org/genproto/googleapis/rpc/status
 google.golang.org/genproto/protobuf/field_mask
 # google.golang.org/grpc v1.42.0
+## explicit
 google.golang.org/grpc
 google.golang.org/grpc/attributes
 google.golang.org/grpc/backoff