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//! This module defines a lexer to recognize tokens of the shell language.
use self::TokenOrLiteral::*;
use std::iter::{Fuse, Peekable};
use super::token::{Positional, Token};
use super::token::Token::*;
#[derive(PartialEq, Eq, Debug, Clone)]
enum TokenOrLiteral {
Tok(Token),
Escaped(Option<Token>),
Lit(char),
}
/// Converts raw characters into shell tokens.
#[must_use = "`Lexer` is lazy and does nothing unless consumed"]
#[derive(Clone, Debug)]
pub struct Lexer<I: Iterator<Item = char>> {
inner: Peekable<Fuse<I>>,
peeked: Option<TokenOrLiteral>,
}
impl<I: Iterator<Item = char>> Lexer<I> {
/// Creates a new Lexer from any char iterator.
pub fn new(iter: I) -> Lexer<I> {
Lexer {
inner: iter.fuse().peekable(),
peeked: None,
}
}
#[inline]
fn next_is(&mut self, c: char) -> bool {
let is = self.inner.peek() == Some(&c);
if is { self.inner.next(); }
is
}
fn next_internal(&mut self) -> Option<TokenOrLiteral> {
if self.peeked.is_some() {
return self.peeked.take();
}
let cur = match self.inner.next() {
Some(c) => c,
None => return None,
};
let tok = match cur {
'\n' => Newline,
'!' => Bang,
'~' => Tilde,
'#' => Pound,
'*' => Star,
'?' => Question,
'%' => Percent,
'-' => Dash,
'=' => Equals,
'+' => Plus,
':' => Colon,
'@' => At,
'^' => Caret,
'/' => Slash,
',' => Comma,
// Make sure that we treat the next token as a single character,
// preventing multi-char tokens from being recognized. This is
// important because something like `\&&` would mean that the
// first & is a literal while the second retains its properties.
// We will let the parser deal with what actually becomes a literal.
'\\' => return Some(Escaped(self.inner.next().and_then(|c| {
Lexer::new(::std::iter::once(c)).next()
}))),
'\'' => SingleQuote,
'"' => DoubleQuote,
'`' => Backtick,
';' => if self.next_is(';') { DSemi } else { Semi },
'&' => if self.next_is('&') { AndIf } else { Amp },
'|' => if self.next_is('|') { OrIf } else { Pipe },
'(' => ParenOpen,
')' => ParenClose,
'{' => CurlyOpen,
'}' => CurlyClose,
'[' => SquareOpen,
']' => SquareClose,
'$' => {
// Positional parameters are 0-9, so we only
// need to check a single digit ahead.
let positional = match self.inner.peek() {
Some(&'0') => Some(Positional::Zero),
Some(&'1') => Some(Positional::One),
Some(&'2') => Some(Positional::Two),
Some(&'3') => Some(Positional::Three),
Some(&'4') => Some(Positional::Four),
Some(&'5') => Some(Positional::Five),
Some(&'6') => Some(Positional::Six),
Some(&'7') => Some(Positional::Seven),
Some(&'8') => Some(Positional::Eight),
Some(&'9') => Some(Positional::Nine),
_ => None,
};
match positional {
Some(p) => {
self.inner.next(); // Consume the character we just peeked
ParamPositional(p)
},
None => Dollar,
}
},
'<' => if self.next_is('<') {
if self.next_is('-') { DLessDash } else { DLess }
} else if self.next_is('&') {
LessAnd
} else if self.next_is('>') {
LessGreat
} else {
Less
},
'>' => if self.next_is('&') {
GreatAnd
} else if self.next_is('>') {
DGreat
} else if self.next_is('|') {
Clobber
} else {
Great
},
// Newlines are valid whitespace, however, we want to tokenize them separately!
c if c.is_whitespace() => {
let mut buf = String::new();
buf.push(c);
// NB: Can't use filter here because it will advance the iterator too far.
while let Some(&c) = self.inner.peek() {
if c.is_whitespace() && c != '\n' {
self.inner.next();
buf.push(c);
} else {
break
}
}
Whitespace(buf)
},
c => return Some(Lit(c)),
};
Some(Tok(tok))
}
}
impl<I: Iterator<Item = char>> Iterator for Lexer<I> {
type Item = Token;
fn next(&mut self) -> Option<Token> {
fn name_start_char(c: char) -> bool {
c == '_' || c.is_alphabetic()
}
fn is_digit(c: char) -> bool {
c.is_digit(10)
}
fn name_char(c: char) -> bool {
is_digit(c) || name_start_char(c)
}
match self.next_internal() {
None => None,
Some(Tok(t)) => Some(t),
Some(Escaped(t)) => {
debug_assert_eq!(self.peeked, None);
self.peeked = t.map(Tok);
Some(Backslash)
},
Some(Lit(c)) => {
let is_name = name_start_char(c);
let mut word = String::new();
word.push(c);
loop {
match self.next_internal() {
// If we hit a token, delimit the current word w/o losing the token
Some(tok@Tok(_)) |
Some(tok@Escaped(_)) => {
debug_assert_eq!(self.peeked, None);
self.peeked = Some(tok);
break;
},
// Make sure we delimit valid names whenever a non-name char comes along
Some(Lit(c)) if is_name && !name_char(c) => {
debug_assert_eq!(self.peeked, None);
self.peeked = Some(Lit(c));
return Some(Name(word));
},
// Otherwise, keep consuming characters for the literal
Some(Lit(c)) => word.push(c),
None => break,
}
}
if is_name {
Some(Name(word))
} else {
Some(Literal(word))
}
},
}
}
fn size_hint(&self) -> (usize, Option<usize>) {
// The number of actual tokens we yield will never exceed
// the amount of characters we are processing. In practice
// the caller will probably see a lot fewer tokens than
// number of characters processed, however, they can prepare
// themselves for the worst possible case. A high estimate
// is better than no estimate.
let (_, hi) = self.inner.size_hint();
let low = if self.peeked.is_some() { 1 } else { 0 };
(low, hi)
}
}