nushell/crates/nu_plugin_example/src/example.rs

use nu_plugin::{EvaluatedCall, LabeledError};
use nu_protocol::Value;
pub struct Example;

impl Example {
    fn print_values(
        &self,
        index: u32,
        call: &EvaluatedCall,
        input: &Value,
    ) -> Result<(), LabeledError> {
        // Note. When debugging your plugin, you may want to print something to the console
        // Use the eprintln macro to print your messages. Trying to print to stdout will
        // cause a decoding error for your message
        eprintln!("Calling test {} signature", index);
        eprintln!("value received {:?}", input);

        // To extract the arguments from the Call object you can use the functions req, has_flag,
        // opt, rest, and get_flag
        //
        // Note that plugin calls only accept simple arguments, this means that you can
        // pass to the plug in Int and String. This should be improved when the plugin has
        // the ability to call back to NuShell to extract more information
        // Keep this in mind when designing your plugin signatures
        let a: i64 = call.req(0)?;
        let b: String = call.req(1)?;
        let flag = call.has_flag("flag");
        let opt: Option<i64> = call.opt(2)?;
        let named: Option<String> = call.get_flag("named")?;
        let rest: Vec<String> = call.rest(3)?;

        eprintln!("Required values");
        eprintln!("a: {:}", a);
        eprintln!("b: {:}", b);
        eprintln!("flag: {:}", flag);
        eprintln!("rest: {:?}", rest);

        match opt {
            Some(v) => eprintln!("Found optional value opt: {:}", v),
            None => eprintln!("No optional value found"),
        }

        match named {
            Some(v) => eprintln!("Named value: {:?}", v),
            None => eprintln!("No named value found"),
        }

        Ok(())
    }

    pub fn test1(&self, call: &EvaluatedCall, input: &Value) -> Result<Value, LabeledError> {
        self.print_values(1, call, input)?;

        Ok(Value::Nothing { span: call.head })
    }

    pub fn test2(&self, call: &EvaluatedCall, input: &Value) -> Result<Value, LabeledError> {
        self.print_values(2, call, input)?;

        let cols = vec!["one".to_string(), "two".to_string(), "three".to_string()];

        let vals = (0..10i64)
            .map(|i| {
                let vals = (0..3)
                    .map(|v| Value::Int {
                        val: v * i,
                        span: call.head,
                    })
                    .collect::<Vec<Value>>();

                Value::Record {
                    cols: cols.clone(),
                    vals,
                    span: call.head,
                }
            })
            .collect::<Vec<Value>>();

        Ok(Value::List {
            vals,
            span: call.head,
        })
    }

    pub fn test3(&self, call: &EvaluatedCall, input: &Value) -> Result<Value, LabeledError> {
        self.print_values(3, call, input)?;

        Err(LabeledError {
            label: "ERROR from plugin".into(),
            msg: "error message pointing to call head span".into(),
            span: Some(call.head),
        })
    }
}