Getting Go to recognize when new line is added to a TOML config file

Question

I am trying to create a simple cli tool in Go using a TOML config file. I want to be able to store frequent commands I use on the command line for other tools, in a TOML file and use my CLI program to recall those. I want to make adding a new tool / command to the TOML file as easy as possible for other users. The trouble I am having is getting Go to recognize a new tool added to the TOML config file, without manually opening my config.go file and adding the tool to the config struct that is holding the parsed TOML data. Example TOML config:

# Configuration File
#
[assetfinder]
default = "assetfinder -subs-only {{TARGET}}"
silent = "assetfinder -subs-only {{TARGET}} --silent"

[subfinder]
default = "subfinder -u {{TARGET}}"
silent = "subfinder -u {{TARGET}} --silent"

I want a user to be able to add another tool/command without having to touch the source code and manually add it to the struct. Here is config.go:

package config

import (
    "github.com/spf13/viper"
)

type Config struct {
    Assetfinder map[string]string
    Subfinder map[string]string
}

func Load() (*Config, error) {
    v := viper.New()
    v.SetConfigName("config")
    v.AddConfigPath(".")
    err := v.ReadInConfig()
    if err != nil {
        return nil, err
    }
    c := &Config{}
    err = v.Unmarshal(c)
    return c, err
}

Answer 1

The viper has a solution about "Watching and re-reading config files". https://github.com/spf13/viper#watching-and-re-reading-config-files.

You just need to register to OnConfigChange event and call WatchConfig:

err := v.ReadInConfig()
if err != nil {
    return nil, err
}
viper.OnConfigChange(func(e fsnotify.Event) {
    fmt.Println("Config file changed:", e.Name)
    // TODO: read config from viper and update you logic
})
viper.WatchConfig()

The WatchConfig implements is in https://github.com/spf13/viper/blob/master/viper.go#L431

1. it use fsnotify to watch file change
2. when file create/write, it call ReadInConfig to update
3. trigger onConfigChange event