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//! Boa's lexer cursor that manages the input byte stream.
use crate::source::{ReadChar, UTF8Input};
use boa_ast::{LinearPosition, Position, PositionGroup, SourceText};
use std::io::{self, Error, ErrorKind};
/// Cursor over the source code.
#[derive(Debug)]
pub(super) struct Cursor<R> {
iter: R,
pos: Position,
module: bool,
strict: bool,
peeked: [Option<u32>; 4],
source_collector: SourceText,
}
impl<R> Cursor<R> {
/// Gets the current position of the cursor in the source code.
#[inline]
pub(super) fn pos_group(&self) -> PositionGroup {
PositionGroup::new(self.pos, self.linear_pos())
}
/// Gets the current position of the cursor in the source code.
#[inline]
pub(super) const fn pos(&self) -> Position {
self.pos
}
/// Gets the current linear position of the cursor in the source code.
#[inline]
pub(super) fn linear_pos(&self) -> LinearPosition {
self.source_collector.cur_linear_position()
}
pub(super) fn take_source(&mut self) -> SourceText {
let replace_with = SourceText::with_capacity(0);
std::mem::replace(&mut self.source_collector, replace_with)
}
/// Advances the position to the next column.
fn next_column(&mut self) {
let current_line = self.pos.line_number();
let next_column = self.pos.column_number() + 1;
self.pos = Position::new(current_line, next_column);
}
/// Advances the position to the next line.
fn next_line(&mut self) {
let next_line = self.pos.line_number() + 1;
self.pos = Position::new(next_line, 1);
}
/// Returns if strict mode is currently active.
pub(super) const fn strict(&self) -> bool {
self.strict
}
/// Sets the current strict mode.
pub(super) fn set_strict(&mut self, strict: bool) {
self.strict = strict;
}
/// Returns if the module mode is currently active.
pub(super) const fn module(&self) -> bool {
self.module
}
/// Sets the current goal symbol to module.
pub(super) fn set_module(&mut self, module: bool) {
self.module = module;
self.strict = module;
}
}
impl<R: ReadChar> Cursor<R> {
/// Creates a new Lexer cursor.
pub(super) fn new(inner: R) -> Self {
Self {
iter: inner,
pos: Position::new(1, 1),
strict: false,
module: false,
peeked: [None; 4],
source_collector: SourceText::default(),
}
}
/// Peeks the next n bytes, the maximum number of peeked bytes is 4 (n <= 4).
pub(super) fn peek_n(&mut self, n: u8) -> Result<&[Option<u32>; 4], Error> {
let peeked = self.peeked.iter().filter(|c| c.is_some()).count();
let needs_peek = n as usize - peeked;
for i in 0..needs_peek {
let next = self.iter.next_char()?;
self.peeked[i + peeked] = next;
}
Ok(&self.peeked)
}
/// Peeks the next UTF-8 character in u32 code point.
pub(super) fn peek_char(&mut self) -> Result<Option<u32>, Error> {
if let Some(c) = self.peeked[0] {
return Ok(Some(c));
}
let next = self.iter.next_char()?;
self.peeked[0] = next;
Ok(next)
}
pub(super) fn next_if(&mut self, c: u32) -> io::Result<bool> {
if self.peek_char()? == Some(c) {
self.next_char()?;
Ok(true)
} else {
Ok(false)
}
}
/// Applies the predicate to the next character and returns the result.
/// Returns false if the next character is not a valid ascii or there is no next character.
/// Otherwise returns the result from the predicate on the ascii in char
///
/// The buffer is not incremented.
pub(super) fn next_is_ascii_pred<F>(&mut self, pred: &F) -> io::Result<bool>
where
F: Fn(char) -> bool,
{
Ok(match self.peek_char()? {
Some(byte) if (0..=0x7F).contains(&byte) =>
{
#[allow(clippy::cast_possible_truncation)]
pred(char::from(byte as u8))
}
Some(_) | None => false,
})
}
/// Fills the buffer with all bytes until the stop byte is found.
/// Returns error when reaching the end of the buffer.
///
/// Note that all bytes up until the stop byte are added to the buffer, including the byte right before.
pub(super) fn take_until(&mut self, stop: u32, buf: &mut Vec<u32>) -> io::Result<()> {
loop {
if self.next_if(stop)? {
return Ok(());
} else if let Some(c) = self.next_char()? {
buf.push(c);
} else {
return Err(Error::new(
ErrorKind::UnexpectedEof,
format!("Unexpected end of file when looking for character {stop}"),
));
}
}
}
/// Fills a mutable slice up to the ends while characters are alphabetic. Returns
/// the number of characters read, or `N+1` if the buffer was filled but there were
/// still characters after.
pub(super) fn take_array_alphabetic<const N: usize>(
&mut self,
arr: &mut [u32; N],
) -> io::Result<usize> {
for (i, out) in arr.iter_mut().enumerate() {
match self.peek_char()? {
// A..Z | a..z
Some(0x41..=0x5A | 0x61..=0x7A) => {
*out = self.next_char()?.expect("Already checked.");
}
_ => return Ok(i),
}
}
// Check the next character and return N+1 if it's alphabetic.
match self.peek_char() {
// A..Z | a..z
Ok(Some(0x41..=0x5A | 0x61..=0x7A)) => Ok(N + 1),
_ => Ok(N),
}
}
/// Retrieves the next UTF-8 character.
pub(crate) fn next_char(&mut self) -> Result<Option<u32>, Error> {
let ch = if let Some(c) = self.peeked[0] {
self.peeked[0] = None;
self.peeked.rotate_left(1);
Some(c)
} else {
self.iter.next_char()?
};
if let Some(ch) = ch {
self.source_collector.collect_code_point(ch);
}
match ch {
Some(0xD) => {
// Try to take a newline if it's next, for windows "\r\n" newlines
// Otherwise, treat as a Mac OS9 bare '\r' newline
if self.peek_char()? == Some(0xA) {
self.peeked[0] = None;
self.peeked.rotate_left(1);
self.source_collector.collect_code_point(0xA);
}
self.next_line();
}
// '\n' | '\u{2028}' | '\u{2029}'
Some(0xA | 0x2028 | 0x2029) => self.next_line(),
Some(_) => self.next_column(),
_ => {}
}
Ok(ch)
}
}
impl<'a> From<&'a [u8]> for Cursor<UTF8Input<&'a [u8]>> {
fn from(input: &'a [u8]) -> Self {
Self::new(UTF8Input::new(input))
}
}