Provide CLI arguments in config file

[SamuelMarks]

Please complete the following tasks

• I have searched the discussions
• I have searched the open and rejected issues

Clap Version

4.4.0

Describe your use case

Writing version and daemon managers. So you begin by downloading, installing, and starting a package. Then you stop, install-service (daemon).

Either by including all the arguments with you every step of the way, or using a config file.

Describe the solution you'd like

My use case:

• Store JSON of version → all provided CLI arguments (uses ENV if not provided otherwise the default value)

To give a concrete of what the JSON would look like:

{
  "15.3.1": {
    "Port": 5430,
    "Database": "my_15_3_db",
    "Username": "thespp",
    "Password": "cxvsd",
  },
  "15.4.0": {
    "Port": 5432,
    "Database": "my_15_4_db",
    "Username": "cvxvx",
    "Password": "45j45lF",
  }
}

Alternatives, if applicable

Working prototype (in Go, but planning a Rust rewrite): https://github.com/offscale/postgres-version-manager-go

I suppose I could use
https://github.com/aobatact/clap-serde

Or straight up serde on the struct in question and use it that way. But there seems to be a lot of intricacies to consider, like how do I know when:

• A default value has been overriden by an env var or by a CLI arg or given in a config file

Also how do I deserialise it with a version per JSON key. It was pretty hacky to get working in Go.

Additional Context

Related: #3113

That way you can either provide this JSON file in a --config or it will use the default location (assuming you don't have --no-config-write set).

[epage]

Closing in favor of #2763