mapstructure-to-hcl

mapstructure-to-hcl Helps generate the code necessary for any plugin, including the core plugins to communicate the HCL2 layout of a plugin with Packer, for Example, with the following config.go file:

//go:generate packer-sdc mapstructure-to-hcl2 -type Config

// Config helps configure things
type Config struct {

Will generate a config.hcl2spec.go file containing a FlatConfig struct, which is a struct with all the mapstructure nested fields 'flattened' into the FlatConfig, so nothing is nested. The FlatConfig struct will get a HCL2Spec function that describes its HCL2 layout. This will be used to read and validate actual HCL2 files. The config.hcl2spec.go will also add a FlatMapstructure function to the Config struct. That function returns a FlatConfig. These functions together define an interface meant for a plugin component to 'speak' the HCL2 language with the Packer core.

Before HCL2, Packer JSON heavily relied on the mapstructure decoding library to load/parse user config files, making this part of the code very tested. To go to HCL2 this command was created.

Here are a few differences/gaps betweens HCL2 and mapstructure:

• in HCL2 all basic struct fields (string/int/struct) that are not pointers are required ( must be set ). In mapstructure everything is optional.
• mapstructure allows to 'squash' fields (ex: Field CommonStructType mapstructure:",squash") this allows to decorate structs and reuse configuration code. HCL2 parsing libs don't have anything similar.