What does ArgAction use for? (clap crate)

[aurexav]

https://docs.rs/clap/latest/clap/enum.ArgAction.html

I found some projects that made an update like:

#[derive(Debug, Parser)]
pub struct S {
-	#[clap(long)]
+	#[clap(long, action)]
	pub output: Option<PathBuf>,
}

But it looks like nothing different (for the execution result).

What does the action used for?

I'm also using clap on my project. So, I'd like to figure out how it works.

[epage]

Huh, never documented this in the reference. #4043 fixes that.

It opts you into clap v4's new semantics. In this particular example, it switches from the old default of ArgAction::StoreValue to ArgAction::Set. It also implies #[clap(value_parser)] which will cause the PathBuf to not go through UTF-8 validation and will implicitly set the completions to ValueHint::AnyPath.