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|
//! A general parser for command-line options.
//!
//! exa uses its own hand-rolled parser for command-line options. It supports
//! the following syntax:
//!
//! - Long options: `--inode`, `--grid`
//! - Long options with values: `--sort size`, `--level=4`
//! - Short options: `-i`, `-G`
//! - Short options with values: `-ssize`, `-L=4`
//!
//! These values can be mixed and matched: `exa -lssize --grid`. If you’ve used
//! other command-line programs, then hopefully it’ll work much like them.
//!
//! Because exa already has its own files for the help text, shell completions,
//! man page, and readme, so it can get away with having the options parser do
//! very little: all it really needs to do is parse a slice of strings.
//!
//!
//! ## UTF-8 and `OsStr`
//!
//! The parser uses `OsStr` as its string type. This is necessary for exa to
//! list files that have invalid UTF-8 in their names: by treating file paths
//! as bytes with no encoding, a file can be specified on the command-line and
//! be looked up without having to be encoded into a `str` first.
//!
//! It also avoids the overhead of checking for invalid UTF-8 when parsing
//! command-line options, as all the options and their values (such as
//! `--sort size`) are guaranteed to just be 8-bit ASCII.
use std::ffi::{OsStr, OsString};
use std::fmt;
use crate::options::Misfire;
/// A **short argument** is a single ASCII character.
pub type ShortArg = u8;
/// A **long argument** is a string. This can be a UTF-8 string, even though
/// the arguments will all be unchecked OsStrings, because we don’t actually
/// store the user’s input after it’s been matched to a flag, we just store
/// which flag it was.
pub type LongArg = &'static str;
/// A **list of values** that an option can have, to be displayed when the
/// user enters an invalid one or skips it.
///
/// This is literally just help text, and won’t be used to validate a value to
/// see if it’s correct.
pub type Values = &'static [&'static str];
/// A **flag** is either of the two argument types, because they have to
/// be in the same array together.
#[derive(PartialEq, Debug, Clone)]
pub enum Flag {
Short(ShortArg),
Long(LongArg),
}
impl Flag {
pub fn matches(&self, arg: &Arg) -> bool {
match *self {
Flag::Short(short) => arg.short == Some(short),
Flag::Long(long) => arg.long == long,
}
}
}
impl fmt::Display for Flag {
fn fmt(&self, f: &mut fmt::Formatter) -> Result<(), fmt::Error> {
match *self {
Flag::Short(short) => write!(f, "-{}", short as char),
Flag::Long(long) => write!(f, "--{}", long),
}
}
}
/// Whether redundant arguments should be considered a problem.
#[derive(PartialEq, Debug, Copy, Clone)]
pub enum Strictness {
/// Throw an error when an argument doesn’t do anything, either because
/// it requires another argument to be specified, or because two conflict.
ComplainAboutRedundantArguments,
/// Search the arguments list back-to-front, giving ones specified later
/// in the list priority over earlier ones.
UseLastArguments,
}
/// Whether a flag takes a value. This is applicable to both long and short
/// arguments.
#[derive(Copy, Clone, PartialEq, Debug)]
pub enum TakesValue {
/// This flag has to be followed by a value.
/// If there’s a fixed set of possible values, they can be printed out
/// with the error text.
Necessary(Option<Values>),
/// This flag will throw an error if there’s a value after it.
Forbidden,
/// This flag may be followed by a value to override its defaults
Optional(Option<Values>),
}
/// An **argument** can be matched by one of the user’s input strings.
#[derive(PartialEq, Debug)]
pub struct Arg {
/// The short argument that matches it, if any.
pub short: Option<ShortArg>,
/// The long argument that matches it. This is non-optional; all flags
/// should at least have a descriptive long name.
pub long: LongArg,
/// Whether this flag takes a value or not.
pub takes_value: TakesValue,
}
impl fmt::Display for Arg {
fn fmt(&self, f: &mut fmt::Formatter) -> Result<(), fmt::Error> {
write!(f, "--{}", self.long)?;
if let Some(short) = self.short {
write!(f, " (-{})", short as char)?;
}
Ok(())
}
}
/// Literally just several args.
#[derive(PartialEq, Debug)]
pub struct Args(pub &'static [&'static Arg]);
impl Args {
/// Iterates over the given list of command-line arguments and parses
/// them into a list of matched flags and free strings.
pub fn parse<'args, I>(&self, inputs: I, strictness: Strictness) -> Result<Matches<'args>, ParseError>
where I: IntoIterator<Item=&'args OsString> {
use std::os::unix::ffi::OsStrExt;
use self::TakesValue::*;
let mut parsing = true;
// The results that get built up.
let mut result_flags = Vec::new();
let mut frees: Vec<&OsStr> = Vec::new();
// Iterate over the inputs with “while let” because we need to advance
// the iterator manually whenever an argument that takes a value
// doesn’t have one in its string so it needs the next one.
let mut inputs = inputs.into_iter();
while let Some(arg) = inputs.next() {
let bytes = arg.as_bytes();
// Stop parsing if one of the arguments is the literal string “--”.
// This allows a file named “--arg” to be specified by passing in
// the pair “-- --arg”, without it getting matched as a flag that
// doesn’t exist.
if !parsing {
frees.push(arg)
}
else if arg == "--" {
parsing = false;
}
// If the string starts with *two* dashes then it’s a long argument.
else if bytes.starts_with(b"--") {
let long_arg_name = OsStr::from_bytes(&bytes[2..]);
// If there’s an equals in it, then the string before the
// equals will be the flag’s name, and the string after it
// will be its value.
if let Some((before, after)) = split_on_equals(long_arg_name) {
let arg = self.lookup_long(before)?;
let flag = Flag::Long(arg.long);
match arg.takes_value {
Necessary(_)|Optional(_) => result_flags.push((flag, Some(after))),
Forbidden => return Err(ParseError::ForbiddenValue { flag })
}
}
// If there’s no equals, then the entire string (apart from
// the dashes) is the argument name.
else {
let arg = self.lookup_long(long_arg_name)?;
let flag = Flag::Long(arg.long);
match arg.takes_value {
Forbidden => result_flags.push((flag, None)),
Necessary(values) => {
if let Some(next_arg) = inputs.next() {
result_flags.push((flag, Some(next_arg)));
}
else {
return Err(ParseError::NeedsValue { flag, values })
}
},
Optional(_) => {
if let Some(next_arg) = inputs.next() {
result_flags.push((flag, Some(next_arg)));
}
else {
result_flags.push((flag, None));
}
}
}
}
}
// If the string starts with *one* dash then it’s one or more
// short arguments.
else if bytes.starts_with(b"-") && arg != "-" {
let short_arg = OsStr::from_bytes(&bytes[1..]);
|