Allow "extra" or "meta" data in YAML configuration files

[cbzehner]

👋 Thanks so much for building clap, it makes Rust CLIs a joy to write!

I'm working on a small project right now where I'm using <bin>.yaml files to build up multiple binaries. Each <bin>.yaml file generates a different binary.

For each generated binary the clap::App and every clap::Arg have a few extra settings that I want users to be able to configure at build-time. Right now I'm handling this by splitting each binary into two configs:

1. A <bin>.yaml file for building the Clap CLI (this will be used for internationalization)
2. A second yaml file that provides some extra data for each clap::App and every clap::Arg used in the application logic.

Ideally, I'd like to include the values from #2 in the binary-specific yaml files (<bin>.yaml) as extra fields and then either (a) fetch the extra data with a ArgMatch::value_of("metadata") or (b) allow the extra field to exist in the From trait and manually parse it myself.

Would y'all be open to either approach? Do you have other suggestions for how I could go about solving this?

PS - As part of investigating this yesterday, I noticed that the From trait validates the fields on the Args but doesn't validate the fields on the App? I'm not sure if this is intentional or an oversight, but the behavior seems inconsistent. I created a minimal example showcasing the inconsistent behavior. Let me know if you'd like me to open an issue.

[pksunkara]

I am not exactly sure what you are asking or trying to do. Need more information.

And I don't think we really care about the extra fields.

[cbzehner]

Please let me know how I can clarify what I'm trying to do (if you're interested). My question is:

Currently Args::from_yaml validates that any field contained in the args: key of a yaml file is in a list of allowed fields and panics on non-allowed fields. However, the implementation of the From trait for App checks the fields needed for Clap and silently ignores extra fields.

Ideally, I'd like the Args::from_yaml to behave the same way as the From<&Yaml> for App and not panic!(...) on invalid or extraneous fields.

[cbzehner]

For now I'm solving this by just including my extra fields at the clap::App level of the config, which works well-enough for my purposes.

[pksunkara]

You can send a PR to our master branch (v3) to ignore fields for Arg too.