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//! Scanner helpers: split source into lines while tracking byte offsets.
//!
//! Byte offsets (not line/column) are what the parser and tokenizer attach to
//! nodes; a JS editor like CodeMirror/Monaco converts offsets to positions on
//! its own, and offsets are cheaper to carry around.
/// Yield `(byte_offset, line_without_eol)` for each line of `source`.
pub(crate) fn lines_with_offsets(source: &str) -> Vec<(usize, &str)> {
let mut out = Vec::new();
let mut start = 0usize;
for raw in source.split_inclusive('\n') {
let full_len = raw.len();
let content = raw.strip_suffix('\n').unwrap_or(raw);
let content = content.strip_suffix('\r').unwrap_or(content);
out.push((start, content));
start += full_len;
}
out
}
/// Retained text fragments with a piecewise map back to the original buffer. A span across a gap encloses the removed bytes; a span on either side
/// maps to that side. No per-byte table: generated text (verbatim padding or
/// expanded tabs) is one segment pinned to the source bytes it replaces.
#[derive(Clone)]
pub(crate) struct FilteredSource {
pub text: String,
pub removed: Vec<crate::Span>,
segments: Vec<Segment>,
}
/// A run of the transformed text starting at `start` that maps to `original`.
/// Generated text maps every position to `original`; a span ending in it ends
/// after the `width` source bytes it replaces (zero for padding).
#[derive(Clone, Copy)]
struct Segment {
start: usize,
original: usize,
generated: Option<usize>,
}
/// A piece of a [`FilteredSource::remap`] result: a range of the source's
/// text, or generated text standing for the source range `at..at + width`.
pub(crate) enum Piece {
Copy(std::ops::Range<usize>),
Generated {
text: String,
at: usize,
width: usize,
},
}
impl FilteredSource {
pub fn from_fragments<'a>(fragments: impl IntoIterator<Item = (usize, &'a str)>) -> Self {
let mut result = Self {
text: String::new(),
removed: Vec::new(),
segments: Vec::new(),
};
for (offset, text) in fragments {
if !text.is_empty() {
result.segments.push(Segment {
start: result.text.len(),
original: offset,
generated: None,
});
result.text.push_str(text);
}
}
result
}
/// Text a processor generated for a block: every position maps to the
/// block at `at` (`width` source bytes).
pub fn generated(text: &str, at: usize, width: usize) -> Self {
Self {
text: text.to_owned(),
removed: Vec::new(),
segments: vec![Segment {
start: 0,
original: at,
generated: Some(width),
}],
}
}
pub fn restore_inlines(&self, inlines: &mut [crate::Inline]) {
struct Restore<'a>(&'a FilteredSource);
impl crate::visit::VisitorMut for Restore<'_> {
fn visit_span(&mut self, span: &mut crate::Span) {
*span = self.0.original_span(*span);
}
}
crate::visit::walk_inlines_mut(&mut Restore(self), inlines);
}
/// Retain the first line: a slice may begin after a list/admonition prefix.
pub fn without_lines(src: &str, base: usize, remove: impl Fn(&str) -> bool) -> Self {
Self::without_lines_at(src, base, |_, line| remove(line))
}
/// [`FilteredSource::without_lines`] whose predicate also gets the line's
/// offset in `src`.
pub fn without_lines_at(src: &str, base: usize, remove: impl Fn(usize, &str) -> bool) -> Self {
let mut result = Self {
text: String::new(),
removed: Vec::new(),
segments: Vec::new(),
};
let mut off = base;
for (index, raw) in src.split_inclusive('\n').enumerate() {
let line = raw.trim_end_matches(['\n', '\r']);
if index > 0 && remove(off - base, line) {
result.removed.push(crate::Span::new(off, off + line.len()));
} else {
result.segments.push(Segment {
start: result.text.len(),
original: off,
generated: None,
});
result.text.push_str(raw);
}
off += raw.len();
}
// Removing trailing comments must not add a final soft line break.
let len = result.text.trim_end_matches(['\n', '\r']).len();
result.text.truncate(len);
result
}
/// A new text assembled from `pieces` of this one, keeping the map back
/// to the original buffer (generated pieces pin to the bytes they stand for).
pub fn remap(&self, pieces: &[Piece]) -> Self {
let mut result = Self {
text: String::new(),
removed: self.removed.clone(),
segments: Vec::new(),
};
for piece in pieces {
match piece {
Piece::Copy(range) if range.is_empty() => {}
Piece::Copy(range) => {
if self.segments.is_empty() {
result.segments.push(Segment {
start: result.text.len(),
original: range.start,
generated: None,
});
} else {
let first = self
.segments
.partition_point(|s| s.start <= range.start)
.saturating_sub(1);
for segment in self.segments[first..]
.iter()
.take_while(|s| s.start < range.end)
{
let from = range.start.max(segment.start);
result.segments.push(Segment {
start: result.text.len() + from - range.start,
original: match segment.generated {
Some(_) => segment.original,
None => segment.original + from - segment.start,
},
generated: segment.generated,
});
}
}
result.text.push_str(&self.text[range.clone()]);
}
Piece::Generated { text, .. } if text.is_empty() => {}
Piece::Generated { text, at, width } => {
let original = self.original_span(crate::Span::new(*at, at + width));
result.segments.push(Segment {
start: result.text.len(),
original: original.start,
generated: Some(original.end - original.start),
});
result.text.push_str(text);
}
}
}
result
}
pub fn original_span(&self, span: crate::Span) -> crate::Span {
if self.segments.is_empty() {
return span;
}
let start_idx = self
.segments
.partition_point(|s| s.start <= span.start)
.saturating_sub(1);
let s = self.segments[start_idx];
let start = match s.generated {
Some(_) => s.original,
None => s.original + span.start - s.start,
};
if span.start == span.end {
return crate::Span::new(start, start);
}
let end_idx = self
.segments
.partition_point(|s| s.start < span.end)
.saturating_sub(1);
let e = self.segments[end_idx];
let end = match e.generated {
Some(width) => e.original + width,
None => e.original + span.end - e.start,
};
crate::Span::new(start, end.max(start))
}
}