proposal: Implement serde::Serializer and Source/AsyncSource for Value

[Xuanwo]

I'm working on an app that uses clap for command line args parsing. I want to support loading configs in various ways with the specific rules:

• loading from env
• loading from config files
• loading from args

To avoid duplicate code, I'm trying to use:

struct App {
  #[clap(flatten)]
  config: Config,
}

struct Config {
   ...
}

To make our config values merge correctly, we should take values that parsed via clap as a source:

let mut builder = Config::builder()
    .add_source(Environment::default())
    .add_source(File::new("config/settings", FileFormat::Json))
    .add_source(Config::parse());

In order to make that code works, we need:

• Implement serde::Serializer for Value, so we can build Value from the config struct itself. (Maybe implementing Into<Value> is enough?)
• Implement Source/AsyncSourc for Value, so we can use the value as a source (it's trivial and makes sense, right?)

What do you think about this idea?

[matthiasbeyer]

I am not 100% sure whether this could or even should be done, but I wouldn't mind to see a PR for this.

Please make sure to feature-gate it, so that users of config who don't want to use clap don't have to pull it in! 😄

[Xuanwo]

I am not 100% sure whether this could or even should be done, but I wouldn't mind to see a PR for this.

Sadly, I failed to implement this without a huge refactor on Value. 😢

Let's close this issue.