Clap and rustyline tab completion integration

Cargo.toml

[package]
name = "tmp"
version = "0.1.0"
authors = ["Miccah Castorina <m.castorina93@gmail.com>"]
edition = "2018"

[dependencies]
clap-v3 = { version = "3.0.0-beta.1", features = ["yaml"] }
rustyline = "6.2.0"
serde_yaml = "0.8"

clap.yaml

name: tmp
version: "0.1.0"

settings:
    - NoBinaryName
    - DisableVersion
    - VersionlessSubcommands

subcommands:
    - create:
        settings:
            - SubcommandRequiredElseHelp
            - VersionlessSubcommands
        about: Create an HTTP request or variable
        visible_aliases: ["new", "add", "c"]
        subcommands:
            - request:
                about: Create an HTTP request
                visible_aliases: ["req", "r"]
            - variable:
                about: Create a variable
                visible_aliases: ["var", "v"]
    - show:
        settings:
            - SubcommandRequiredElseHelp
            - VersionlessSubcommands
        about: Print resources
        visible_aliases: ["get", "print", "g", "p"]
        subcommands:
            - requests:
                about: Print requests
                visible_aliases: ["request", "reqs", "req", "r"]
            - variables:
                about: Print variables
                visible_aliases: ["variable", "vars", "var", "v"]
            - environments:
                about: Print environments
                visible_aliases: ["environment", "envs", "env", "e"]
            - workspaces:
                about: Print workspaces
                visible_aliases: ["workspace", "ws", "w"]
            - response:
                about: Print information about the last request and response
                visible_aliases: ["resp", "rr"]
    - set:
        settings:
            - SubcommandRequiredElseHelp
            - VersionlessSubcommands
        about: Set workspace, environment, or request for contextual commands
        visible_aliases: ["use", "load", "u"]
        subcommands:
            - environment:
                about: Set the environment as used for variable substitution
                visible_aliases: ["env", "e"]
            - request:
                about: Set the request to view and modify specific options
                visible_aliases: ["req", "r"]
            - workspace:
                about: Set the workspace where all data is stored
                visible_aliases: ["ws", "w"]
            - variable:
                about: Update or create variable values
                visible_aliases: ["var", "v"]
    - delete:
        settings:
            - SubcommandRequiredElseHelp
            - VersionlessSubcommands
        about: Delete named requests or variables
        visible_aliases: ["remove", "del", "rm"]
        subcommands:
            - requests:
                about: Delete the named HTTP requests
                visible_aliases: ["request", "reqs", "req", "r"]
            - variables:
                about: Delete the named variables
                visible_aliases: ["variable", "vars", "var", "v"]

main.rs

use clap_v3::{load_yaml, App};
use rustyline::completion::{Completer, Pair};
use rustyline::config::OutputStreamType;
use rustyline::error::ReadlineError;
use rustyline::highlight::Highlighter;
use rustyline::hint::Hinter;
use rustyline::validate::Validator;
use rustyline::{CompletionType, Config, Context, EditMode, Editor, Helper};
use serde_yaml::Value;

pub struct LineReader {
    editor: Editor<LineReaderHelper>,
}
impl LineReader {
    pub fn new() -> LineReader {
        // setup rustyline
        let config = Config::builder()
            .completion_type(CompletionType::List)
            .edit_mode(EditMode::Vi)
            .output_stream(OutputStreamType::Stdout)
            .build();
        let clap_yaml: Value = serde_yaml::from_str(include_str!("clap.yaml")).unwrap();
        let h = LineReaderHelper::new(&clap_yaml);
        let mut rl = Editor::with_config(config);
        rl.set_helper(Some(h));

        LineReader { editor: rl }
    }

    pub fn read_line(&mut self, input: &mut String, prompt: &str) -> Option<()> {
        let readline = self.editor.readline(prompt);
        match readline {
            Ok(line) => {
                *input = line;
                Some(())
            }
            Err(ReadlineError::Interrupted) => Some(()),
            Err(ReadlineError::Eof) => None,
            Err(_) => None,
        }
    }
}

pub struct LineReaderHelper {
    root_yaml: Value,
}
impl LineReaderHelper {
    fn new(base_yaml: &Value) -> LineReaderHelper {
        LineReaderHelper {
            root_yaml: base_yaml.clone(),
        }
    }
}

impl Helper for LineReaderHelper {}
impl Hinter for LineReaderHelper {}
impl Highlighter for LineReaderHelper {}
impl Validator for LineReaderHelper {}
impl Completer for LineReaderHelper {
    type Candidate = Pair;
    fn complete(
        &self,
        line: &str,
        pos: usize,
        _ctx: &Context,
    ) -> rustyline::Result<(usize, Vec<Self::Candidate>)> {
        let line = format!("{}_", line);
        let cmd = CommandStructure::from(&self.root_yaml);
        let mut cmd = &cmd;
        // split line
        let mut tokens = line.split_whitespace();
        let mut last_token = String::from(tokens.next_back().unwrap());
        last_token.pop();

        for tok in tokens {
            let next_cmd = cmd.get_child(tok);
            if next_cmd.is_none() {
                return Ok((pos, vec![]));
            }
            cmd = next_cmd.unwrap();
        }

        let candidates: Vec<String> = cmd
            .completions
            .to_vec()
            .into_iter()
            .filter(|x| x.starts_with(&last_token))
            .collect();
        Ok((
            line.len() - last_token.len() - 1,
            candidates
                .iter()
                .map(|cmd| Pair {
                    display: String::from(cmd),
                    replacement: format!("{} ", cmd),
                })
                .collect(),
        ))
    }
}

struct CommandStructure {
    name: String,                         // command name
    aliases: Vec<String>,                 // possible aliases for name
    completions: Vec<String>,             // subcommand names
    children: Vec<Box<CommandStructure>>, // list of commands (name should match a completion)
}

impl CommandStructure {
    fn new(name: &str) -> CommandStructure {
        CommandStructure {
            name: String::from(name),
            aliases: vec![],
            completions: vec![],
            children: vec![],
        }
    }
    fn get_child<'a>(&'a self, name_or_alias: &str) -> Option<&'a CommandStructure> {
        for cs in self.children.iter() {
            if cs.name == name_or_alias || cs.aliases.iter().any(|e| e == name_or_alias) {
                return Some(cs);
            }
        }
        None
    }
}

impl From<&serde_yaml::Value> for CommandStructure {
    fn from(value: &serde_yaml::Value) -> CommandStructure {
        let (name, value) = get_map(value);
        let mut cs = CommandStructure::new(name);
        cs.aliases = get_aliases(&value)
            .into_iter()
            .map(|x| String::from(x))
            .collect();
        cs.completions = get_sub_names(&value)
            .into_iter()
            .map(|x| String::from(x))
            .collect();

        let subcommands = value.get("subcommands");
        if subcommands.is_none() {
            return cs;
        }
        let subcommands = subcommands.unwrap();
        if let Value::Sequence(cmds) = subcommands {
            for cmd in cmds {
                cs.children.push(Box::new(CommandStructure::from(cmd)));
            }
        }
        cs
    }
}
fn get_map(cmd: &Value) -> (&str, &Value) {
    let name = get_name(cmd).unwrap();
    (name, cmd.get(name).unwrap_or(cmd))
}
fn get_aliases(cmd: &Value) -> Vec<&str> {
    let mut names = vec![];
    if let Value::Mapping(m) = cmd {
        for kv in m.iter() {
            let (k, v) = kv;
            match k.as_str().unwrap() {
                "aliases" | "visible_aliases" => {
                    if let Value::Sequence(aliases) = v {
                        for alias in aliases {
                            names.push(alias.as_str().unwrap());
                        }
                    }
                }
                _ => (),
            }
        }
    }
    names
}
fn get_name(cmd: &Value) -> Option<&str> {
    if let Some(v) = cmd.get("name") {
        if v.is_string() {
            return Some(v.as_str().unwrap());
        }
    }
    if let Value::Mapping(m) = cmd {
        for kv in m.iter() {
            let (k, _) = kv;
            // should only be one mapping
            return k.as_str();
        }
    }
    None
}
fn get_sub_names(cmd: &Value) -> Vec<&str> {
    let mut names = vec![];
    let subcommands = cmd.get("subcommands");
    if subcommands.is_none() {
        return names;
    }
    let subcommands = subcommands.unwrap();
    if let Value::Sequence(cmds) = subcommands {
        for cmd in cmds {
            let name = get_name(cmd);
            if name.is_some() {
                names.push(name.unwrap());
            }
        }
    }
    names
}

fn main() {
    let mut line_reader = LineReader::new();
    let mut input = String::new();
    let yaml = load_yaml!("clap.yaml");
    loop {
        let app = App::from(yaml);
        if line_reader.read_line(&mut input, "> ") == None {
            break;
        }
        let matches = app.try_get_matches_from(input.split_whitespace());
        if let Err(err) = matches {
            println!("{}", err);
            continue;
        }
        match matches.unwrap().subcommand() {
            ("create", Some(matches)) => match matches.subcommand() {
                ("request", _) => println!(" ** create request **"),
                ("variable", _) => println!(" ** create variable **"),
                _ => unreachable!(),
            },
            ("show", Some(matches)) => match matches.subcommand() {
                ("requests", _) => println!(" ** show requests **"),
                ("variables", _) => println!(" ** show variables **"),
                ("options", _) => println!(" ** show options **"),
                ("environments", _) => println!(" ** show environments **"),
                ("workspaces", _) => println!(" ** show workspaces **"),
                ("response", _) => println!(" ** show response **"),
                _ => unreachable!(),
            },
            ("set", Some(matches)) => match matches.subcommand() {
                ("workspace", _) => println!(" ** set workspace **"),
                ("environment", _) => println!(" ** set environment **"),
                ("request", _) => println!(" ** set request **"),
                ("option", _) => println!(" ** set option **"),
                ("variable", _) => println!(" ** set variable **"),
                _ => unreachable!(),
            },
            ("delete", Some(matches)) => match matches.subcommand() {
                ("requests", _) => println!(" ** delete requests **"),
                ("variables", _) => println!(" ** delete variables **"),
                ("options", _) => println!(" ** delete options **"),
                _ => unreachable!(),
            },
            _ => unreachable!(),
        }
    }
}