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Rust @programming.dev Kirsten Freitag @programming.dev 1y ago

clap::_derive::_tutorial - Rust

docs.rs clap::_derive::_tutorial - Rust

Documentation: Derive Tutorial

I've tried to run the example under "Configuring the Parser" and get some errors. What could be my problem?

Errors

error: cannot find derive macro Parser in this scope
error: cannot find attribute command in this scope
error: cannot find attribute arg in this scope
error[E0599]: no function or associated item named parse found for struct Cli in the current scope

Cargo.toml

[package]
name = "hello_cargo"
version = "0.1.0"
edition = "2021"

[dependencies]
clap = "4.3.5"

7 comments

The tutorial makes a reference to this

This requires enabling the derive feature flag.

But if you aren't as familiar with feature flags, this isn't as helpful.

More specifically on the front page we have

$ cargo add clap --features derive

Maybe we should push that down into the tutorial...
- That's the point. I didn't know about the feature flags feature of Rust/Cargo. Of course, if you know it, you "have to" skip it in each tutorial. IMHO, it should be okay 🙂 Thank you for your answer.
try

clap = { version = "4.3", features = ["derive"] }
- Thanks a lot. That's it. But, what have I done now 😀 ? I believe I misunderstand the dependency inclusion. I have to learn something about features and why they aren't activated by default.
  
  a crate may contain may different parts, and you may not always want all of them to avoid bloat. For an example, a crate may contain a sync and an async version, but you will probably only want one of them. So then the crate exposes the different parts as features. In clap they have defined the default features as:
  
  default = ["std", "color", "help", "usage", "error-context", "suggestions"]
  
  So, then if you need to use functionality not included there, then you have to specify it in your features list. On https://docs.rs/crate/clap/latest you can find a drop down in the top menu with Feature Flags, then they also have the documentation for the feature flags here https://docs.rs/clap/latest/clap/_features/index.html

7 comments