rustyline 8.0.0

Rustyline, a readline implementation based on Antirez's Linenoise
Documentation 
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use smallvec::smallvec;
use std::borrow::Cow::{self, Borrowed, Owned};

use rustyline::highlight::Highlighter;
use rustyline::hint::{Hinter, HistoryHinter};
use rustyline::{
    Cmd, ConditionalEventHandler, Context, Editor, Event, EventContext, EventHandler, KeyEvent,
    RepeatCount,
};
use rustyline_derive::{Completer, Helper, Validator};

#[derive(Completer, Helper, Validator)]
struct MyHelper(HistoryHinter);

impl Hinter for MyHelper {
    type Hint = String;

    fn hint(&self, line: &str, pos: usize, ctx: &Context<'_>) -> Option<String> {
        self.0.hint(line, pos, ctx)
    }
}

impl Highlighter for MyHelper {
    fn highlight_prompt<'b, 's: 'b, 'p: 'b>(
        &'s self,
        prompt: &'p str,
        default: bool,
    ) -> Cow<'b, str> {
        if default {
            Owned(format!("\x1b[1;32m{}\x1b[m", prompt))
        } else {
            Borrowed(prompt)
        }
    }

    fn highlight_hint<'h>(&self, hint: &'h str) -> Cow<'h, str> {
        Owned(format!("\x1b[1m{}\x1b[m", hint))
    }
}

#[derive(Clone)]
struct CompleteHintHandler;
impl ConditionalEventHandler for CompleteHintHandler {
    fn handle(&self, evt: &Event, _: RepeatCount, _: bool, ctx: &EventContext) -> Option<Cmd> {
        if !ctx.has_hint() {
            return None; // default
        }
        if let Some(k) = evt.get(0) {
            #[allow(clippy::if_same_then_else)]
            if *k == KeyEvent::ctrl('E') {
                Some(Cmd::CompleteHint)
            } else if *k == KeyEvent::alt('f') && ctx.line().len() == ctx.pos() {
                Some(Cmd::CompleteHint) // TODO give access to hint
            } else {
                None
            }
        } else {
            unreachable!()
        }
    }
}

struct TabEventHandler;
impl ConditionalEventHandler for TabEventHandler {
    fn handle(&self, evt: &Event, n: RepeatCount, _: bool, ctx: &EventContext) -> Option<Cmd> {
        debug_assert_eq!(*evt, Event::from(KeyEvent::from('\t')));
        if ctx.line()[..ctx.pos()]
            .chars()
            .rev()
            .next()
            .filter(|c| c.is_whitespace())
            .is_some()
        {
            Some(Cmd::SelfInsert(n, '\t'))
        } else {
            None // default complete
        }
    }
}

fn main() {
    let mut rl = Editor::<MyHelper>::new();
    rl.set_helper(Some(MyHelper(HistoryHinter {})));

    let ceh = Box::new(CompleteHintHandler);
    rl.bind_sequence(KeyEvent::ctrl('E'), EventHandler::Conditional(ceh.clone()));
    rl.bind_sequence(KeyEvent::alt('f'), EventHandler::Conditional(ceh));
    rl.bind_sequence(
        KeyEvent::from('\t'),
        EventHandler::Conditional(Box::new(TabEventHandler)),
    );
    rl.bind_sequence(
        Event::KeySeq(smallvec![KeyEvent::ctrl('X'), KeyEvent::ctrl('E')]),
        EventHandler::Simple(Cmd::Suspend), // TODO external editor
    );

    loop {
        let readline = rl.readline("> ");
        match readline {
            Ok(line) => {
                rl.add_history_entry(line.as_str());
                println!("Line: {}", line);
            }
            Err(err) => {
                println!("Error: {:?}", err);
                break;
            }
        }
    }
}