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107 lines
3 KiB
Rust
107 lines
3 KiB
Rust
use ruff_text_size::{TextLen, TextSize};
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use std::str::Chars;
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pub(crate) const EOF_CHAR: char = '\0';
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#[derive(Clone, Debug)]
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pub(super) struct Cursor<'a> {
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chars: Chars<'a>,
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source_length: TextSize,
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#[cfg(debug_assertions)]
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prev_char: char,
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}
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impl<'a> Cursor<'a> {
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pub(crate) fn new(source: &'a str) -> Self {
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Self {
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source_length: source.text_len(),
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chars: source.chars(),
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#[cfg(debug_assertions)]
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prev_char: EOF_CHAR,
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}
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}
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/// Returns the previous token. Useful for debug assertions.
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#[cfg(debug_assertions)]
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pub(super) const fn previous(&self) -> char {
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self.prev_char
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}
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/// Peeks the next character from the input stream without consuming it.
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/// Returns [`EOF_CHAR`] if the file is at the end of the file.
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pub(super) fn first(&self) -> char {
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self.chars.clone().next().unwrap_or(EOF_CHAR)
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}
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/// Peeks the second character from the input stream without consuming it.
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/// Returns [`EOF_CHAR`] if the position is past the end of the file.
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pub(super) fn second(&self) -> char {
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let mut chars = self.chars.clone();
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chars.next();
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chars.next().unwrap_or(EOF_CHAR)
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}
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/// Returns the remaining text to lex.
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pub(super) fn rest(&self) -> &'a str {
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self.chars.as_str()
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}
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// SAFETY: The `source.text_len` call in `new` would panic if the string length is larger than a `u32`.
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#[allow(clippy::cast_possible_truncation)]
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pub(super) fn text_len(&self) -> TextSize {
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TextSize::new(self.chars.as_str().len() as u32)
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}
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pub(super) fn token_len(&self) -> TextSize {
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self.source_length - self.text_len()
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}
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pub(super) fn start_token(&mut self) {
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self.source_length = self.text_len();
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}
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pub(super) fn is_eof(&self) -> bool {
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self.chars.as_str().is_empty()
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}
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/// Consumes the next character
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pub(super) fn bump(&mut self) -> Option<char> {
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let prev = self.chars.next()?;
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#[cfg(debug_assertions)]
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{
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self.prev_char = prev;
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}
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Some(prev)
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}
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pub(super) fn eat_char(&mut self, c: char) -> bool {
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if self.first() == c {
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self.bump();
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true
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} else {
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false
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}
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}
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pub(super) fn eat_if<F>(&mut self, mut predicate: F) -> Option<char>
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where
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F: FnMut(char) -> bool,
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{
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if predicate(self.first()) && !self.is_eof() {
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self.bump()
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} else {
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None
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}
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}
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/// Eats symbols while predicate returns true or until the end of file is reached.
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pub(super) fn eat_while(&mut self, mut predicate: impl FnMut(char) -> bool) {
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// It was tried making optimized version of this for eg. line comments, but
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// LLVM can inline all of this and compile it down to fast iteration over bytes.
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while predicate(self.first()) && !self.is_eof() {
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self.bump();
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}
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}
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}
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