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//! Source code spans.
//!
//! The [`DefaultEmitter`](crate::DefaultEmitter) is generic over a [`Span`].
//! This library comes with two Span implementations:
//!
//! * one for `()` which acts as the no-op implementation for when you don't want to track spans
//! * one for [`Range<usize>`] for when you do want to track spans
//!
//! To use the latter your reader however has to implement [`GetPos`].
//! You can easily use any existing reader by wrapping it in the [`PosTracker`] struct
//! which implements the [`GetPos`] trait and takes care of tracking the current position.
use std::ops::Range;
use crate::Reader;
/// A trait to be implemented by readers that track their own position.
pub trait GetPos {
/// Returns the byte index of the current position.
fn get_pos(&self) -> usize;
}
/// Wraps a [`Reader`] so that it implements [`GetPos`].
pub struct PosTracker<R> {
/// The wrapped reader.
pub reader: R,
/// The current position.
pub position: usize,
}
impl<R> GetPos for PosTracker<R> {
fn get_pos(&self) -> usize {
self.position
}
}
/// Represents a character range in the source code.
pub trait Span<R>: Default + Clone {
/// Initializes a new span at the current position of the reader.
fn from_reader(reader: &R) -> Self;
/// Initializes a new span at the current position of the reader with the given offset.
fn from_reader_with_offset(reader: &R, offset: usize) -> Self;
/// Extends the span by the length of the given string.
fn push_str(&mut self, str: &str);
}
impl<R> Span<R> for () {
fn from_reader(_reader: &R) -> Self {}
fn from_reader_with_offset(_reader: &R, _offset: usize) -> Self {}
fn push_str(&mut self, _str: &str) {}
}
impl<P: GetPos> Span<P> for Range<usize> {
fn from_reader(reader: &P) -> Self {
reader.get_pos() - 1..reader.get_pos() - 1
}
fn from_reader_with_offset(reader: &P, offset: usize) -> Self {
reader.get_pos() - 1 + offset..reader.get_pos() - 1 + offset
}
fn push_str(&mut self, str: &str) {
self.end += str.len();
}
}
impl<R: Reader> Reader for PosTracker<R> {
type Error = R::Error;
fn read_char(&mut self) -> Result<Option<char>, Self::Error> {
match self.reader.read_char()? {
Some(char) => {
self.position += char.len_utf8();
Ok(Some(char))
}
None => Ok(None),
}
}
fn try_read_string(&mut self, s: &str, case_sensitive: bool) -> Result<bool, Self::Error> {
match self.reader.try_read_string(s, case_sensitive)? {
true => {
self.position += s.len();
Ok(true)
}
false => Ok(false),
}
}
}
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