mapstructure example

main.go

package main

import (
	"fmt"

	"github.com/mitchellh/mapstructure"
)

type moduleConfig struct {
	ModuleBool bool `yaml:"module-bool" mapstructure:"module-bool"`
}

type specialModuleConfig struct {
	*moduleConfig     `yaml:",inline" mapstructure:",squash"`
	SpecialModuleBool bool `yaml:"special-module-bool" mapstructure:"special-module-bool"`
}

type TopLevelConfig struct {
	Module1 moduleConfig        `yaml:"module-1" mapstructure:"module-1"`
	Module2 specialModuleConfig `yaml:"module-2" mapstructure:"module-2"`
}

func main() {
	theMap := map[string]any{
		"module-1": map[string]any{
			"module-bool": true,
		},
		"module-2": map[string]any{
			"module-bool":         true,
			"special-module-bool": true,
		},
	}

	configPtr := &TopLevelConfig{}

	mapstructure.Decode(theMap, configPtr)

	fmt.Printf("%+v\n", *configPtr)
}

Running this fails to populate the the embedded struct:

❯ go run main.go
{Module1:{ModuleBool:true} Module2:{moduleConfig:<nil> SpecialModuleBool:true}}

But if I remove the * on the beginning of line 14, the code works as expected:

❯ vi main.go # remove * from beginning of line 14
❯ go run main.go
{Module1:{ModuleBool:true} Module2:{moduleConfig:{ModuleBool:true} SpecialModuleBool:true}}

It looks like maybe this is a language limitation, not a mapstructure limitation: https://go-review.googlesource.com/c/go/+/53643.

There's some interesting discussion at golang/go#21357.