build: add experimental support for print flag

Print flag can be used to make additional information
requests about the build and print their results.

Currently Dockerfile supports: outline, targets, subrequests.describe

Signed-off-by: Tonis Tiigi <tonistiigi@gmail.com>

vendor/github.com/moby/buildkit/frontend/subrequests/outline/outline.go

@@ -0,0 +1,146 @@
+package outline
+
+import (
+	"bytes"
+	"encoding/json"
+	"fmt"
+	"io"
+	"text/tabwriter"
+
+	"github.com/moby/buildkit/frontend/gateway/client"
+	"github.com/moby/buildkit/frontend/subrequests"
+	"github.com/moby/buildkit/solver/pb"
+)
+
+const RequestSubrequestsOutline = "frontend.outline"
+
+var SubrequestsOutlineDefinition = subrequests.Request{
+	Name:        RequestSubrequestsOutline,
+	Version:     "1.0.0",
+	Type:        subrequests.TypeRPC,
+	Description: "List all parameters current build target supports",
+	Opts: []subrequests.Named{
+		{
+			Name:        "target",
+			Description: "Target build stage",
+		},
+	},
+	Metadata: []subrequests.Named{
+		{Name: "result.json"},
+		{Name: "result.txt"},
+	},
+}
+
+type Outline struct {
+	Name        string       `json:"name,omitempty"`
+	Description string       `json:"description,omitempty"`
+	Args        []Arg        `json:"args,omitempty"`
+	Secrets     []Secret     `json:"secrets,omitempty"`
+	SSH         []SSH        `json:"ssh,omitempty"`
+	Cache       []CacheMount `json:"cache,omitempty"`
+	Sources     [][]byte     `json:"sources,omitempty"`
+}
+
+func (o Outline) ToResult() (*client.Result, error) {
+	res := client.NewResult()
+	dt, err := json.MarshalIndent(o, "", "  ")
+	if err != nil {
+		return nil, err
+	}
+	res.AddMeta("result.json", dt)
+
+	b := bytes.NewBuffer(nil)
+	if err := PrintOutline(dt, b); err != nil {
+		return nil, err
+	}
+	res.AddMeta("result.txt", b.Bytes())
+
+	res.AddMeta("version", []byte(SubrequestsOutlineDefinition.Version))
+	return res, nil
+}
+
+type Arg struct {
+	Name        string       `json:"name"`
+	Description string       `json:"description,omitempty"`
+	Value       string       `json:"value,omitempty"`
+	Location    *pb.Location `json:"location,omitempty"`
+}
+
+type Secret struct {
+	Name     string       `json:"name"`
+	Required bool         `json:"required,omitempty"`
+	Location *pb.Location `json:"location,omitempty"`
+}
+
+type SSH struct {
+	Name     string       `json:"name"`
+	Required bool         `json:"required,omitempty"`
+	Location *pb.Location `json:"location,omitempty"`
+}
+
+type CacheMount struct {
+	ID       string       `json:"ID"`
+	Location *pb.Location `json:"location,omitempty"`
+}
+
+func PrintOutline(dt []byte, w io.Writer) error {
+	var o Outline
+
+	if err := json.Unmarshal(dt, &o); err != nil {
+		return err
+	}
+
+	if o.Name != "" || o.Description != "" {
+		tw := tabwriter.NewWriter(w, 0, 0, 1, ' ', 0)
+		name := o.Name
+		if o.Name == "" {
+			name = "(default)"
+		}
+		fmt.Fprintf(tw, "TARGET:\t%s\n", name)
+		if o.Description != "" {
+			fmt.Fprintf(tw, "DESCRIPTION:\t%s\n", o.Description)
+		}
+		tw.Flush()
+		fmt.Println()
+	}
+
+	if len(o.Args) > 0 {
+		tw := tabwriter.NewWriter(w, 0, 0, 3, ' ', 0)
+		fmt.Fprintf(tw, "BUILD ARG\tVALUE\tDESCRIPTION\n")
+		for _, a := range o.Args {
+			fmt.Fprintf(tw, "%s\t%s\t%s\n", a.Name, a.Value, a.Description)
+		}
+		tw.Flush()
+		fmt.Println()
+	}
+
+	if len(o.Secrets) > 0 {
+		tw := tabwriter.NewWriter(w, 0, 0, 3, ' ', 0)
+		fmt.Fprintf(tw, "SECRET\tREQUIRED\n")
+		for _, s := range o.Secrets {
+			b := ""
+			if s.Required {
+				b = "true"
+			}
+			fmt.Fprintf(tw, "%s\t%s\n", s.Name, b)
+		}
+		tw.Flush()
+		fmt.Println()
+	}
+
+	if len(o.SSH) > 0 {
+		tw := tabwriter.NewWriter(w, 0, 0, 3, ' ', 0)
+		fmt.Fprintf(tw, "SSH\tREQUIRED\n")
+		for _, s := range o.SSH {
+			b := ""
+			if s.Required {
+				b = "true"
+			}
+			fmt.Fprintf(tw, "%s\t%s\n", s.Name, b)
+		}
+		tw.Flush()
+		fmt.Println()
+	}
+
+	return nil
+}