Support for partially running a DAG

Signed-off-by: Andrea Luzzardi <aluzzardi@gmail.com>

cmd/dagger/cmd/up.go

@@ -145,8 +145,8 @@ func europaUp(ctx context.Context, cl *client.Client, args ...string) error {
 	p, err := plan.Load(ctx, plan.Config{
 		Args:   args,
 		With:   viper.GetStringSlice("with"),
+		Target: viper.GetString("target"),
 	})
-
 	if err != nil {
 		lg.Fatal().Err(err).Msg("failed to load plan")
 	}
@@ -225,6 +225,7 @@ func init() {
 	upCmd.Flags().BoolP("force", "f", false, "Force up, disable inputs check")
 	upCmd.Flags().String("output", "", "Write computed output. Prints on stdout if set to-")
 	upCmd.Flags().StringArrayP("with", "w", []string{}, "")
+	upCmd.Flags().StringP("target", "t", "", "Run a single target of the DAG (for debugging only)")
 
 	if err := viper.BindPFlags(upCmd.Flags()); err != nil {
 		panic(err)

plan/plan.go

@@ -28,6 +28,7 @@ type Plan struct {
 type Config struct {
 	Args   []string
 	With   []string
+	Target string
 }
 
 func Load(ctx context.Context, cfg Config) (*Plan, error) {
@@ -149,10 +150,17 @@ func (p *Plan) Up(ctx context.Context, s solver.Solver) (*compiler.Value, error)
 
 	computed := compiler.NewValue()
 
-	flow := cueflow.New(
-		&cueflow.Config{
+	cfg := &cueflow.Config{
 		FindHiddenTasks: true,
-		},
+	}
+	if p.config.Target != "" {
+		cfg.Root = cue.ParsePath(p.config.Target)
+		// The target may reference dependencies outside of the target path.
+		// InferTasks will include them in the workflow.
+		cfg.InferTasks = true
+	}
+	flow := cueflow.New(
+		cfg,
 		p.source.Cue(),
 		newRunner(p.context, s, computed),
 	)