Mapping raw args to desired type on-the-fly similar to `serde_with::TryFromInto`

[MrFoxPro]

Clap Version

4.5.42

Describe your use case

Due to limitations of clap, it's not always possible to get desired type from CLI: example.
Same thing applies to serde, but there is convenient macro serde_with::TryFromInto, which allows in combination with #[serde(flatten)] to map values into desired type.

Describe the solution you'd like

Something like serde_with::TryFromInto, but for clap.

Additional Context

It's difficult to transform CLI input to different type, especially if there are multiple nested subcommands. Right now it requires a lot of boilerplate.

[epage]

It would help if you provided a concrete example, like code you tried but is failing.

There are two things I can think you mean:

• An individual argument type is unsupported. We have the value_parser attribute for this. To see what all conversions are supported for that, see https://docs.rs/clap/latest/clap/macro.value_parser.html. That means we support FromStr but not TryFrom for failable operations though we do support try_map on other value parsers.
• A group of arguments (like Support for using ArgGroup as Enum with derive #2621). This requires implementing traits directly, see https://docs.rs/clap/latest/clap/_derive/index.html#mixing-builder-and-derive-apis

If its one of those cases, could you clarify why the current solutions aren't meeting your needs?