add args to exec

d2plugin/exec.go

@@ -113,7 +113,11 @@ func (p execPlugin) Layout(ctx context.Context, g *d2graph.Graph) error {
 		return err
 	}
 
-	cmd := exec.CommandContext(ctx, p.path, "layout")
+	args := []string{"layout"}
+	for k, v := range p.opts {
+		args = append(args, k, v)
+	}
+	cmd := exec.CommandContext(ctx, p.path, args...)
 
 	buffer := bytes.Buffer{}
 	buffer.Write(graphBytes)

d2plugin/serve.go

@@ -38,6 +38,8 @@ func Serve(p Plugin) xmain.RunFunc {
 		switch subcmd {
 		case "info":
 			return info(ctx, p, ms)
+		case "flags":
+			return flags(ctx, p, ms)
 		case "layout":
 			return layout(ctx, p, ms)
 		case "postprocess":
@@ -64,6 +66,22 @@ func info(ctx context.Context, p Plugin, ms *xmain.State) error {
 	return nil
 }
 
+func flags(ctx context.Context, p Plugin, ms *xmain.State) error {
+	flags, err := p.Flags(ctx)
+	if err != nil {
+		return err
+	}
+	b, err := json.Marshal(flags)
+	if err != nil {
+		return err
+	}
+	_, err = ms.Stdout.Write(b)
+	if err != nil {
+		return err
+	}
+	return nil
+}
+
 func layout(ctx context.Context, p Plugin, ms *xmain.State) error {
 	in, err := io.ReadAll(ms.Stdin)
 	if err != nil {