A minimal command-line utility framework built with zero external dependencies. This tool attempts to retain type information throughout the entire lifecycle of a command parse with the intent of lifting validation of a command's handler to compile-time verifiable.
- Type-safe evaluators and handlers
- Easy-to-use
- Easy to extend via a trait-based api.
ShortHelpable: Short help documentation generatorsHelpable: help documentation generatorsEvauatable: Flag and argument parsersDispatchers: Handler executors
- rust 1.50+
Currently this is not available on crates.io and must be installed via git.
scrap = { git = "https://github.com/ncatelli/scrap", branch = "main" }use scrap::prelude::v1::*;
use std::env;
fn main() {
let raw_args: Vec<String> = env::args().into_iter().collect::<Vec<String>>();
let args = raw_args.iter().map(|a| a.as_str()).collect::<Vec<&str>>();
// The `Flag` type defines helpers for generating various common flag
// evaluators.
// Shown below, the `help` flag represents common boolean flag with default
// a default value.
let help = scrap::Flag::store_true("help", "h", "output help information.")
.optional()
.with_default(false);
// `direction` provides a flag with a finite set of choices, matching a
// string value.
let direction = scrap::Flag::with_choices(
"direction",
"d",
"a cardinal direction.",
[
"north".to_string(),
"south".to_string(),
"east".to_string(),
"west".to_string(),
],
scrap::StringValue,
);
// `Cmd` defines the named command, combining metadata without our above defined command.
let cmd = scrap::Cmd::new("basic")
.description("A minimal example cli.")
.author("John Doe <jdoe@example.com>")
.version("1.2.3")
.with_flag(help)
.with_flag(direction)
// Finally a handler is defined with its signature being a product of
// the cli's defined flags.
.with_handler(|(_, direction)| println!("You chose {}.", direction));
// The help method generates a help command based on the output rendered
// from all defined flags.
let help_string = cmd.help();
// Evaluate attempts to parse the input, evaluating all commands and flags
// into concrete types which can be passed to `dispatch`, the defined
// handler.
let res =
cmd.evaluate(&args[..])
.map_err(|e| e.to_string())
.and_then(|Value { span, value }| match value {
(help, direction) if !help => {
cmd.dispatch(Value::new(span, (help, direction)));
Ok(())
}
_ => Err("output help".to_string()),
});
match res {
Ok(_) => (),
Err(_) => println!("{}", help_string),
}
}The cli supports both a flat command, and a hierarchical set of commands, both covered in the following examples:
The API for extending commands is built around three primary traits.
Evaluatable provides the functionality to evaluate a given input for a match. Below defines an example of an evaluator that reads any &str at the head of the input, converting it into a String.
impl<'a> Evaluatable<'a, &'a [&'a str], String> for StringValue {
fn evaluate(&self, input: &'a [&'a str]) -> EvaluateResult<'a, String> {
input
.get(0)
.map(|v| v.to_string())
.ok_or(CliError::ValueEvaluation)
}
}Evaluatable provides a simple input-output functionality allowing Evaluatable types to be composed. An example of this functionality is the Join, which merges the outputs of two Evaluatables (which we will call E1 and E2) into a tuple, (O1, O2).
#[derive(Debug)]
pub struct Join<E1, E2> {
evaluator1: E1,
evaluator2: E2,
}
impl<E1, E2> IsFlag for Join<E1, E2> {}
impl<E1, E2> Join<E1, E2> {
/// Instantiates a new instance of Join with two given evaluators.
pub fn new(evaluator1: E1, evaluator2: E2) -> Self {
Self {
evaluator1,
evaluator2,
}
}
}
impl<'a, E1, E2, A, B, C> Evaluatable<'a, A, (B, C)> for Join<E1, E2>
where
A: Copy + std::borrow::Borrow<A> + 'a,
E1: Evaluatable<'a, A, B>,
E2: Evaluatable<'a, A, C>,
{
fn evaluate(&self, input: A) -> EvaluateResult<'a, (B, C)> {
self.evaluator1
.evaluate(input)
.map_err(|e| e)
.and_then(|e1_res| match self.evaluator2.evaluate(input) {
Ok(e2_res) => Ok((e1_res, e2_res)),
Err(e) => Err(e),
})
}
}Helpable provides the behavior for generating help strings from any given object. This allows for the building of a cli's help string solely from its consituent parts. A basic example of a common helpable definition.
impl<H> Helpable for Cmd<(), H> {
type Output = String;
fn help(&self) -> Self::Output {
format!(
"Usage: {} [OPTIONS]\n{}\nFlags:\n",
self.name, self.description,
)
}
}ShortHelpable, much like Helpable provides the behavior for generating short-help strings. This can be thought of as the consituent parts of a larger help string.
Dispatchable provides a method, dispatch whose signature is equivalent to the output of all Flag Evaluatables.
impl<'a, E1, E2, A, B, C> Evaluatable<'a, A, (B, C)> for Join<E1, E2>
where
A: Copy + std::borrow::Borrow<A> + 'a,
E1: Evaluatable<'a, A, B>,
E2: Evaluatable<'a, A, C>,
{
fn evaluate(&self, input: A) -> EvaluateResult<'a, (B, C)> {
self.evaluator1
.evaluate(input)
.map_err(|e| e)
.and_then(|e1_res| match self.evaluator2.evaluate(input) {
Ok(e2_res) => Ok((e1_res, e2_res)),
Err(e) => Err(e),
})
}
}If given the above Evaluatable A cli's implemented dispatchable would take an Fn((B, C)) and yield whatever return type is defined for the closure.
DispatchableWithArgs provides a method, dispatch_with_args whose signature is equivalent to the output of all Flag Evaluatables and a Vec<Value<String>> of all unmatched arguments.
To illustrate this behavior, I will reference the above Join.
impl<'a, E1, E2, A, B, C> Evaluatable<'a, A, (B, C)> for Join<E1, E2>
where
A: Copy + std::borrow::Borrow<A> + 'a,
E1: Evaluatable<'a, A, B>,
E2: Evaluatable<'a, A, C>,
{
fn evaluate(&self, input: A) -> EvaluateResult<'a, (B, C)> {
self.evaluator1
.evaluate(input)
.map_err(|e| e)
.and_then(|e1_res| match self.evaluator2.evaluate(input) {
Ok(e2_res) => Ok((e1_res, e2_res)),
Err(e) => Err(e),
})
}
}If given the above Evaluatable A cli's implemented dispatchable would take an Fn(Vec<Value<String>>, (B, C)) and yield whatever return type is defined for the closure.
DispatchableWithHelpString provides a method, dispatch_with_help_string and dispatch_with_supplied_helpstring whose signature is equivalent to the output of all Flag Evaluatables and a preceeding String.
To illustrate this behavior, I will reference the above Join.
impl<'a, E1, E2, A, B, C> Evaluatable<'a, A, (B, C)> for Join<E1, E2>
where
A: Copy + std::borrow::Borrow<A> + 'a,
E1: Evaluatable<'a, A, B>,
E2: Evaluatable<'a, A, C>,
{
fn evaluate(&self, input: A) -> EvaluateResult<'a, (B, C)> {
self.evaluator1
.evaluate(input)
.map_err(|e| e)
.and_then(|e1_res| match self.evaluator2.evaluate(input) {
Ok(e2_res) => Ok((e1_res, e2_res)),
Err(e) => Err(e),
})
}
}DispatchableWithHelpStringAndArgs provides a method, dispatch_with_help_string_and_args and dispatch_with_supplied_helpstring_and_args whose signature is equivalent to the output of all Flag Evaluatables and a preceeding String, along with all unparsed arguments.
To illustrate this behavior, I will reference the above Join.
impl<'a, E1, E2, A, B, C> Evaluatable<'a, A, (B, C)> for Join<E1, E2>
where
A: Copy + std::borrow::Borrow<A> + 'a,
E1: Evaluatable<'a, A, B>,
E2: Evaluatable<'a, A, C>,
{
fn evaluate(&self, input: A) -> EvaluateResult<'a, (B, C)> {
self.evaluator1
.evaluate(input)
.map_err(|e| e)
.and_then(|e1_res| match self.evaluator2.evaluate(input) {
Ok(e2_res) => Ok((e1_res, e2_res)),
Err(e) => Err(e),
})
}
}If given the above Evaluatable A cli's implemented dispatchable would take an Fn(String, Vec<Value<String>>, (B, C)) and yield whatever return type is defined for the closure.
To illustrate how easy it is to write custom Evaluator implementations, I will show an example of a WithOpen evaluator below, which takes an evaluator that yields a type marked Openable and attempts to open the resulting value as a file.
pub trait Openable {}
#[derive(Debug)]
pub struct WithOpen<E> {
evaluator: E,
}
impl<E> IsFlag for WithOpen<E> {}
impl<E> WithOpen<E> {
pub fn new(evaluator: E) -> Self {
Self { evaluator }
}
}
impl<'a, E, A> Evaluatable<'a, A, std::fs::File> for WithOpen<E>
where
A: 'a,
E: Evaluatable<'a, A, String> + Openable,
{
fn evaluate(&self, input: A) -> EvaluateResult<'a, std::fs::File> {
self.evaluator.evaluate(input).and_then(|fp| {
std::fs::File::open(&fp).map_err(|e| {
CliError::FlagEvaluation(format!("unable to open file evaluator: {}", e))
})
})
}
}
impl<E> ShortHelpable for WithOpen<E>
where
E: ShortHelpable<Output = FlagHelpCollector> + Defaultable,
{
type Output = FlagHelpCollector;
fn short_help(&self) -> Self::Output {
match self.evaluator.short_help() {
// Provides a small helper for combining strings.
FlagHelpCollector::Single(fhc) => {
FlagHelpCollector::Single(fhc.with_modifier("will_open".to_string()))
}
fhcj => fhcj,
}
}
}Local tests are heavily implemented within doctests and can be run using cargo's build in test subcommand.
$> cargo testThis tool was primarily built to support other projects that shared the same, no dependency goals and restrictions that I am currently working on. Use under the understanding that support for this will be best-effort.