packer-cn/website/source/guides/hcl/component-object-spec/index.html.md.erb

---
layout: guides
page_title: Generating code for config spec.
sidebar_current: hcl-component-object-spec
description: |-
  Learn how to generate the HCL2 configuration of your component easily.
---

# Auto Generate the HCL2 code of a plugin

From v1.5, Packer can be configured using HCL2. Because Packer has so many
builders, provisioner & post-processors, we relied on code generation to
iterate more easily. The good new is that you can benefit from this code
generator to get the HCL2 spec code of your component simply. It's a Go binary
package and is located in [`cmd/mapstructure-to-hcl2`](https://github.com/hashicorp/packer/tree/master/cmd/mapstructure-to-hcl2).

Say you want to configure the `Config` struct of a `Builder` in a package
located in `my/example-plugin/config.go`. Here are some simple steps you can
follow to make it HCL2 enabled:

* run `go install github.com/hashicorp/packer/cmd/mapstructure-to-hcl2`

* Add `//go:generate mapstructure-to-hcl2 -type Config` at the top of
`config.go`

* run `go generate ./my/example-plugin/...`

    This will generate a `my/example-plugin/config.hcl2spec.go` file containing
    the configuration fields of `Config`.

* Make sure that all the nested structs of `Config` are also auto generated the
  same way.

* Now we only need to make Builder implement the interface by adding the
following snippet:

    ```go
    func (b *Builder) ConfigSpec() hcldec.ObjectSpec { return b.config.FlatMapstructure().HCL2Spec() }
    ```

    From now on every time you add or change a field of Config you will need to
    run the `go generate` command again.

A good example of this is the [Config struct of the amazon-ebs builder](https://github.com/hashicorp/packer/blob/master/builder/amazon/ebs/builder.go)