buildctl: add dot output for visualizing llb

usage: buildctl debug dump-llb --dot | dot -Tsvg

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

cmd/buildctl/debug/dumpllb.go

@@ -2,8 +2,10 @@ package debug
 
 import (
 	"encoding/json"
+	"fmt"
 	"io"
 	"os"
+	"strings"
 
 	"github.com/moby/buildkit/client/llb"
 	"github.com/moby/buildkit/solver/pb"
@@ -17,6 +19,12 @@ var DumpLLBCommand = cli.Command{
 	Usage:     "dump LLB in human-readable format. LLB can be also passed via stdin. This command does not require the daemon to be running.",
 	ArgsUsage: "<llbfile>",
 	Action:    dumpLLB,
+	Flags: []cli.Flag{
+		cli.BoolFlag{
+			Name:  "dot",
+			Usage: "Output dot format",
+		},
+	},
 }
 
 func dumpLLB(clicontext *cli.Context) error {
@@ -35,12 +43,16 @@ func dumpLLB(clicontext *cli.Context) error {
 	if err != nil {
 		return err
 	}
+	if clicontext.Bool("dot") {
+		writeDot(ops, os.Stdout)
+	} else {
 		enc := json.NewEncoder(os.Stdout)
 		for _, op := range ops {
 			if err := enc.Encode(op); err != nil {
 				return err
 			}
 		}
+	}
 	return nil
 }
 
@@ -65,3 +77,36 @@ func loadLLB(r io.Reader) ([]llbOp, error) {
 	}
 	return ops, nil
 }
+
+func writeDot(ops []llbOp, w io.Writer) {
+	fmt.Fprintln(w, "digraph {")
+	defer fmt.Fprintln(w, "}")
+	for _, op := range ops {
+		name, shape := attr(op.Digest, op.Op)
+		fmt.Fprintf(w, "  \"%s\" [label=\"%s\" shape=\"%s\"];\n", op.Digest, name, shape)
+	}
+	for _, op := range ops {
+		for i, inp := range op.Op.Inputs {
+			label := ""
+			if eo, ok := op.Op.Op.(*pb.Op_Exec); ok {
+				for _, m := range eo.Exec.Mounts {
+					if int(m.Input) == i && m.Dest != "/" {
+						label = m.Dest
+					}
+				}
+			}
+			fmt.Fprintf(w, "  \"%s\" -> \"%s\" [label=\"%s\"];\n", inp.Digest, op.Digest, label)
+		}
+	}
+}
+
+func attr(dgst digest.Digest, op pb.Op) (string, string) {
+	switch op := op.Op.(type) {
+	case *pb.Op_Source:
+		return op.Source.Identifier, "ellipse"
+	case *pb.Op_Exec:
+		return strings.Join(op.Exec.Meta.Args, " "), "box"
+	default:
+		return dgst.String(), "plaintext"
+	}
+}