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// Shared arg-parsing utility to replace manual `while i < args.len()` loops.
//
// Design decision: struct with `flag()` and `flag_value()` methods that
// handle both `-fVALUE` (attached) and `-f VALUE` (next arg) forms.
// Each method advances the internal position, so the caller doesn't
// manage index arithmetic. Positional args are consumed with `positional()`.
/// Shared argument parser for builtins.
///
/// Replaces the common `while i < args.len()` pattern with a cleaner API.
///
/// # Usage
///
/// ```rust,ignore
/// let mut parser = ArgParser::new(args);
/// while !parser.is_done() {
/// if parser.flag("-v") {
/// verbose = true;
/// } else if let Some(val) = parser.flag_value("-n", "cmd")? {
/// count = val.parse().map_err(|_| format!("cmd: invalid number: '{val}'"))?;
/// } else {
/// files.push(parser.positional().unwrap().to_string());
/// }
/// }
/// ```
pub(crate) struct ArgParser<'a> {
args: &'a [String],
pos: usize,
}
impl<'a> ArgParser<'a> {
pub fn new(args: &'a [String]) -> Self {
Self { args, pos: 0 }
}
/// Returns true if all args have been consumed.
pub fn is_done(&self) -> bool {
self.pos >= self.args.len()
}
/// Peek at current arg without advancing.
pub fn current(&self) -> Option<&'a str> {
self.args.get(self.pos).map(|s| s.as_str())
}
/// Returns remaining args as a slice (from current position).
pub fn rest(&self) -> &'a [String] {
if self.pos < self.args.len() {
&self.args[self.pos..]
} else {
&[]
}
}
/// Advance past current arg.
pub fn advance(&mut self) {
self.pos += 1;
}
/// Try to consume a boolean flag (exact match). Advances if matched.
pub fn flag(&mut self, name: &str) -> bool {
if self.current() == Some(name) {
self.advance();
true
} else {
false
}
}
/// Try to consume any of several boolean flag names. Advances if matched.
pub fn flag_any(&mut self, names: &[&str]) -> bool {
if self.current().is_some_and(|cur| names.contains(&cur)) {
self.advance();
return true;
}
false
}
/// Try to consume a flag with a required value.
///
/// Handles both `-fVALUE` (attached) and `-f VALUE` (next arg) forms.
/// Returns `Ok(Some(value))` if matched, `Err` if matched but no value,
/// `Ok(None)` if current arg doesn't match.
/// Advances past consumed args on success.
pub fn flag_value(
&mut self,
name: &str,
cmd: &str,
) -> std::result::Result<Option<&'a str>, String> {
let arg = match self.args.get(self.pos) {
Some(a) => a.as_str(),
None => return Ok(None),
};
if arg == name {
// Exact match: value is next arg
self.pos += 1;
match self.args.get(self.pos) {
Some(val) => {
self.pos += 1;
Ok(Some(val.as_str()))
}
None => Err(format!("{cmd}: {name} requires an argument")),
}
} else if let Some(rest) = arg.strip_prefix(name) {
// Attached form: -nVALUE
if !rest.is_empty() {
self.pos += 1;
Ok(Some(rest))
} else {
Ok(None)
}
} else {
Ok(None)
}
}
/// Like `flag_value` but for multiple flag names (e.g. `-o` and `--output`).
/// Only the first name supports the attached `-oVALUE` form.
pub fn flag_value_any(
&mut self,
names: &[&str],
cmd: &str,
) -> std::result::Result<Option<&'a str>, String> {
let arg = match self.args.get(self.pos) {
Some(a) => a.as_str(),
None => return Ok(None),
};
for (i, &name) in names.iter().enumerate() {
if arg == name {
self.pos += 1;
return match self.args.get(self.pos) {
Some(val) => {
self.pos += 1;
Ok(Some(val.as_str()))
}
None => Err(format!("{cmd}: {name} requires an argument")),
};
}
// Only try attached form for short flags (first name typically)
if i == 0
&& let Some(rest) = arg.strip_prefix(name).filter(|r| !r.is_empty())
{
self.pos += 1;
return Ok(Some(rest));
}
}
Ok(None)
}
/// Try to consume a flag with a value, silently returning None if
/// the flag matches but no value is available (for lenient parsers).
pub fn flag_value_opt(&mut self, name: &str) -> Option<&'a str> {
let arg = match self.args.get(self.pos) {
Some(a) => a.as_str(),
None => return None,
};
if arg == name {
self.pos += 1;
if let Some(val) = self.args.get(self.pos) {
self.pos += 1;
Some(val.as_str())
} else {
None
}
} else if let Some(rest) = arg.strip_prefix(name) {
if !rest.is_empty() {
self.pos += 1;
Some(rest)
} else {
None
}
} else {
None
}
}
/// Consume current arg as a positional argument. Returns None if done.
pub fn positional(&mut self) -> Option<&'a str> {
let val = self.args.get(self.pos).map(|s| s.as_str())?;
self.pos += 1;
Some(val)
}
/// Check if current arg looks like a flag (starts with `-`, length > 1).
pub fn is_flag(&self) -> bool {
self.args
.get(self.pos)
.map(|s| s.starts_with('-') && s.len() > 1)
.unwrap_or(false)
}
}
#[cfg(test)]
#[allow(clippy::unwrap_used)]
mod tests {
use super::*;
fn args(strs: &[&str]) -> Vec<String> {
strs.iter().map(|s| s.to_string()).collect()
}
#[test]
fn test_flag() {
let a = args(&["-v", "file"]);
let mut p = ArgParser::new(&a);
assert!(p.flag("-v"));
assert!(!p.flag("-v"));
assert_eq!(p.current(), Some("file"));
}
#[test]
fn test_flag_value_separate() {
let a = args(&["-n", "10", "file"]);
let mut p = ArgParser::new(&a);
assert_eq!(p.flag_value("-n", "cmd").unwrap(), Some("10"));
assert_eq!(p.current(), Some("file"));
}
#[test]
fn test_flag_value_attached() {
let a = args(&["-n10", "file"]);
let mut p = ArgParser::new(&a);
assert_eq!(p.flag_value("-n", "cmd").unwrap(), Some("10"));
assert_eq!(p.current(), Some("file"));
}
#[test]
fn test_flag_value_missing() {
let a = args(&["-n"]);
let mut p = ArgParser::new(&a);
assert!(p.flag_value("-n", "cmd").is_err());
}
#[test]
fn test_flag_value_no_match() {
let a = args(&["-v"]);
let mut p = ArgParser::new(&a);
assert_eq!(p.flag_value("-n", "cmd").unwrap(), None);
// Position unchanged
assert_eq!(p.current(), Some("-v"));
}
#[test]
fn test_flag_any() {
let a = args(&["--verbose"]);
let mut p = ArgParser::new(&a);
assert!(p.flag_any(&["-v", "--verbose"]));
assert!(p.is_done());
}
#[test]
fn test_flag_value_any() {
let a = args(&["--output", "file.txt"]);
let mut p = ArgParser::new(&a);
assert_eq!(
p.flag_value_any(&["-o", "--output"], "cmd").unwrap(),
Some("file.txt")
);
}
#[test]
fn test_flag_value_opt_no_value() {
let a = args(&["-n"]);
let mut p = ArgParser::new(&a);
// No value available, returns None without error
assert_eq!(p.flag_value_opt("-n"), None);
}
#[test]
fn test_flag_value_opt_separate() {
let a = args(&["-n", "10", "file"]);
let mut p = ArgParser::new(&a);
assert_eq!(p.flag_value_opt("-n"), Some("10"));
assert_eq!(p.current(), Some("file"));
}
#[test]
fn test_flag_value_opt_attached() {
let a = args(&["-n10", "file"]);
let mut p = ArgParser::new(&a);
assert_eq!(p.flag_value_opt("-n"), Some("10"));
assert_eq!(p.current(), Some("file"));
}
#[test]
fn test_flag_value_any_attached() {
let a = args(&["-ofile.txt"]);
let mut p = ArgParser::new(&a);
assert_eq!(
p.flag_value_any(&["-o", "--output"], "cmd").unwrap(),
Some("file.txt")
);
assert!(p.is_done());
}
#[test]
fn test_flag_value_any_missing() {
let a = args(&["--output"]);
let mut p = ArgParser::new(&a);
assert!(p.flag_value_any(&["-o", "--output"], "cmd").is_err());
}
#[test]
fn test_current() {
let a = args(&["hello"]);
let mut p = ArgParser::new(&a);
assert_eq!(p.current(), Some("hello"));
p.advance();
assert_eq!(p.current(), None);
}
#[test]
fn test_positional() {
let a = args(&["file1", "file2"]);
let mut p = ArgParser::new(&a);
assert_eq!(p.positional(), Some("file1"));
assert_eq!(p.positional(), Some("file2"));
assert!(p.is_done());
}
#[test]
fn test_rest() {
let a = args(&["-v", "cmd", "arg1", "arg2"]);
let mut p = ArgParser::new(&a);
p.advance(); // skip -v
p.advance(); // skip cmd
assert_eq!(p.rest().len(), 2);
}
#[test]
fn test_is_flag() {
let a = args(&["-v", "-", "file", "--long"]);
let mut p = ArgParser::new(&a);
assert!(p.is_flag()); // -v
p.advance();
assert!(!p.is_flag()); // - (single dash)
p.advance();
assert!(!p.is_flag()); // file
p.advance();
assert!(p.is_flag()); // --long
}
}