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sourcemap_builder.rs
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sourcemap_builder.rs
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use oxc_syntax::identifier::{LS, PS};
// Irregular line breaks - '\u{2028}' (LS) and '\u{2029}' (PS)
const LS_OR_PS_FIRST: u8 = 0xE2;
const LS_OR_PS_SECOND: u8 = 0x80;
const LS_THIRD: u8 = 0xA8;
const PS_THIRD: u8 = 0xA9;
/// Line offset table
///
/// Used for tracking lines and columns from byte offsets via binary search.
///
/// Code is adapted from [esbuild](https://github.com/evanw/esbuild/blob/cc74e6042a9f573bf58e1e3f165ebda70af4ad3b/internal/js_printer/js_printer.go#L4806-L4808)
#[derive(Debug)]
pub struct LineOffsetTable {
columns: Option<Vec<usize>>,
byte_offset_to_first: usize,
byte_offset_to_start_of_line: usize,
}
#[allow(clippy::struct_field_names)]
pub struct SourcemapBuilder {
enable_sourcemap: bool,
source_id: u32,
last_generated_update: usize,
last_position: Option<u32>,
last_search_line: usize,
line_offset_tables: Vec<LineOffsetTable>,
sourcemap_builder: sourcemap::SourceMapBuilder,
generated_line: u32,
generated_column: u32,
}
impl Default for SourcemapBuilder {
fn default() -> Self {
Self {
enable_sourcemap: false,
source_id: 0,
last_generated_update: 0,
last_position: None,
last_search_line: 0,
line_offset_tables: vec![],
sourcemap_builder: sourcemap::SourceMapBuilder::new(None),
generated_line: 0,
generated_column: 0,
}
}
}
impl SourcemapBuilder {
pub fn with_name_and_source(&mut self, name: &str, source: &str) {
self.enable_sourcemap = true;
self.line_offset_tables = Self::generate_line_offset_tables(source);
self.source_id = self.sourcemap_builder.add_source(name);
self.sourcemap_builder.set_source_contents(self.source_id, Some(source));
}
pub fn into_sourcemap(self) -> Option<sourcemap::SourceMap> {
self.enable_sourcemap.then(|| self.sourcemap_builder.into_sourcemap())
}
pub fn add_source_mapping(&mut self, output: &[u8], position: u32, name: Option<&str>) {
if self.enable_sourcemap {
if matches!(self.last_position, Some(last_position) if last_position >= position) {
return;
}
let (original_line, original_column) = self.search_original_line_and_column(position);
self.update_generated_line_and_column(output);
let name_id = name.map(|s| self.sourcemap_builder.add_name(s));
self.sourcemap_builder.add_raw(
self.generated_line,
self.generated_column,
original_line,
original_column,
Some(self.source_id),
name_id,
false,
);
self.last_position = Some(position);
}
}
#[allow(clippy::cast_possible_truncation)]
fn search_original_line_and_column(&mut self, position: u32) -> (u32, u32) {
let mut original_line = 0;
for i in self.last_search_line..self.line_offset_tables.len() {
if self.line_offset_tables[i].byte_offset_to_start_of_line > position as usize {
original_line = i - 1;
break;
}
if i == self.line_offset_tables.len() - 1 {
original_line = i;
}
}
self.last_search_line = original_line;
let line = &self.line_offset_tables[original_line];
let mut original_column = (position as usize) - line.byte_offset_to_start_of_line;
if original_column >= line.byte_offset_to_first {
if let Some(cols) = &line.columns {
original_column = cols[original_column - line.byte_offset_to_first];
}
}
(original_line as u32, original_column as u32)
}
#[allow(clippy::cast_possible_truncation)]
fn update_generated_line_and_column(&mut self, output: &[u8]) {
let remaining = &output[self.last_generated_update..];
// Find last line break
let mut line_start_ptr = remaining.as_ptr();
let mut last_line_is_ascii = true;
let mut iter = remaining.iter();
while let Some(&b) = iter.next() {
match b {
b'\n' => {}
b'\r' => {
// Handle Windows-specific "\r\n" newlines
if iter.clone().next() == Some(&b'\n') {
iter.next();
}
}
_ if b.is_ascii() => {
continue;
}
LS_OR_PS_FIRST => {
let next_byte = *iter.next().unwrap();
let next_next_byte = *iter.next().unwrap();
if next_byte != LS_OR_PS_SECOND
|| !matches!(next_next_byte, LS_THIRD | PS_THIRD)
{
last_line_is_ascii = false;
continue;
}
}
_ => {
// Unicode char
last_line_is_ascii = false;
continue;
}
}
// Line break found.
// `iter` is now positioned after line break.
line_start_ptr = iter.as_slice().as_ptr();
self.generated_line += 1;
self.generated_column = 0;
last_line_is_ascii = true;
}
// Calculate column
self.generated_column += if last_line_is_ascii {
// `iter` is now exhausted, so `iter.as_slice().as_ptr()` is pointer to end of `output`
(iter.as_slice().as_ptr() as usize - line_start_ptr as usize) as u32
} else {
let line_byte_offset = line_start_ptr as usize - remaining.as_ptr() as usize;
// TODO: It'd be better if could use `from_utf8_unchecked` here, but we'd need to make this
// function unsafe and caller guarantees `output` contains a valid UTF-8 string
let last_line = std::str::from_utf8(&remaining[line_byte_offset..]).unwrap();
// Mozilla's "source-map" library counts columns using UTF-16 code units
last_line.encode_utf16().count() as u32
};
self.last_generated_update = output.len();
}
fn generate_line_offset_tables(content: &str) -> Vec<LineOffsetTable> {
let mut tables = vec![];
// Process content line-by-line.
// For each line, start by assuming line will be entirely ASCII, and read byte-by-byte.
// If line is all ASCII, UTF-8 columns and UTF-16 columns are the same,
// so no need to create a `columns` Vec. This is the fast path for common case.
// If a Unicode character found, read rest of line char-by-char, populating `columns` Vec.
// At end of line, go back to top of outer loop, and again assume ASCII for next line.
let mut line_byte_offset = 0;
'lines: loop {
tables.push(LineOffsetTable {
columns: None,
// `usize::MAX` so `original_column >= line.byte_offset_to_first` check in
// `search_original_line_and_column` fails if line is all ASCII
byte_offset_to_first: usize::MAX,
byte_offset_to_start_of_line: line_byte_offset,
});
let remaining = &content.as_bytes()[line_byte_offset..];
for (mut byte_offset_from_line_start, b) in remaining.iter().enumerate() {
match b {
b'\n' => {
byte_offset_from_line_start += 1;
}
b'\r' => {
byte_offset_from_line_start += 1;
// Handle Windows-specific "\r\n" newlines
if remaining.get(byte_offset_from_line_start) == Some(&b'\n') {
byte_offset_from_line_start += 1;
}
}
_ if b.is_ascii() => {
continue;
}
_ => {
// Unicode char found.
// Create `columns` Vec, and set `byte_offset_to_first`.
let table = tables.iter_mut().last().unwrap();
table.byte_offset_to_first = byte_offset_from_line_start;
table.columns = Some(vec![]);
let columns = table.columns.as_mut().unwrap();
// Loop through rest of line char-by-char.
// `chunk_byte_offset` in this loop is byte offset from start of this 1st
// Unicode char.
let mut column = byte_offset_from_line_start;
line_byte_offset += byte_offset_from_line_start;
let remaining = &content[line_byte_offset..];
for (mut chunk_byte_offset, ch) in remaining.char_indices() {
for _ in 0..ch.len_utf8() {
columns.push(column);
}
match ch {
'\r' => {
// Handle Windows-specific "\r\n" newlines
chunk_byte_offset += 1;
if remaining.as_bytes().get(chunk_byte_offset) == Some(&b'\n') {
chunk_byte_offset += 1;
columns.push(column + 1);
}
}
'\n' => {
chunk_byte_offset += 1;
}
LS | PS => {
chunk_byte_offset += 3;
}
_ => {
// Mozilla's "source-map" library counts columns using UTF-16 code units
column += ch.len_utf16();
continue;
}
}
// Line break found.
// `chunk_byte_offset` is now the offset of *end* of the line break.
line_byte_offset += chunk_byte_offset;
// Revert back to outer loop for next line
continue 'lines;
}
// EOF.
// One last column entry for EOF position.
columns.push(column);
break 'lines;
}
};
// Line break found.
// `byte_offset_from_line_start` is now the length of line *including* line break.
line_byte_offset += byte_offset_from_line_start;
continue 'lines;
}
// EOF
break;
}
tables
}
}
#[cfg(test)]
mod test {
use super::*;
#[test]
fn builder_ascii() {
assert_mapping("", &[(0, 0, 0)]);
assert_mapping("a", &[(0, 0, 0), (1, 0, 1)]);
assert_mapping("\n", &[(0, 0, 0), (1, 1, 0)]);
assert_mapping("a\n", &[(0, 0, 0), (1, 0, 1), (2, 1, 0)]);
assert_mapping("\na", &[(0, 0, 0), (1, 1, 0), (2, 1, 1)]);
assert_mapping(
"ab\ncd\n\nef",
&[
(0, 0, 0),
(1, 0, 1),
(2, 0, 2),
(3, 1, 0),
(4, 1, 1),
(5, 1, 2),
(6, 2, 0),
(7, 3, 0),
(8, 3, 1),
(9, 3, 2),
],
);
assert_mapping("\r", &[(0, 0, 0), (1, 1, 0)]);
assert_mapping("\r\r", &[(0, 0, 0), (1, 1, 0), (2, 2, 0)]);
assert_mapping("a\ra", &[(0, 0, 0), (1, 0, 1), (2, 1, 0), (3, 1, 1)]);
assert_mapping("\r\n", &[(0, 0, 0), (1, 0, 1), (2, 1, 0)]);
assert_mapping("\r\n\r\n", &[(0, 0, 0), (1, 0, 1), (2, 1, 0), (3, 1, 1), (4, 2, 0)]);
assert_mapping("a\r\na", &[(0, 0, 0), (1, 0, 1), (2, 0, 2), (3, 1, 0), (4, 1, 1)]);
}
#[test]
fn builder_unicode() {
assert_mapping("Ö", &[(0, 0, 0), (2, 0, 1)]);
assert_mapping("ÖÖ", &[(0, 0, 0), (2, 0, 1), (4, 0, 2)]);
assert_mapping("Ö\n", &[(0, 0, 0), (2, 0, 1), (3, 1, 0)]);
assert_mapping("ÖÖ\n", &[(0, 0, 0), (2, 0, 1), (4, 0, 2), (5, 1, 0)]);
assert_mapping("\nÖ", &[(0, 0, 0), (1, 1, 0), (3, 1, 1)]);
assert_mapping("\nÖÖ", &[(0, 0, 0), (1, 1, 0), (3, 1, 1), (5, 1, 2)]);
assert_mapping("Ö\nÖ", &[(0, 0, 0), (2, 0, 1), (3, 1, 0), (5, 1, 1)]);
assert_mapping("\nÖÖ\n", &[(0, 0, 0), (1, 1, 0), (3, 1, 1), (5, 1, 2), (6, 2, 0)]);
assert_mapping("Ö\ra", &[(0, 0, 0), (2, 0, 1), (3, 1, 0), (4, 1, 1)]);
assert_mapping("Ö\r\na", &[(0, 0, 0), (2, 0, 1), (3, 0, 2), (4, 1, 0), (5, 1, 1)]);
}
fn assert_mapping(source: &str, mappings: &[(u32, u32, u32)]) {
let mut builder = SourcemapBuilder::default();
builder.with_name_and_source("x.js", source);
for (position, expected_line, expected_col) in mappings.iter().copied() {
let (line, col) = builder.search_original_line_and_column(position);
assert_eq!(
builder.search_original_line_and_column(position),
(expected_line, expected_col),
"Incorrect mapping for '{source}' - position {position} = line {line}, column {col}"
);
}
}
#[test]
fn add_source_mapping() {
fn create_mappings(source: &str, line: u32, column: u32) {
let mut builder = SourcemapBuilder::default();
builder.with_name_and_source("x.js", source);
let output: Vec<u8> = source.as_bytes().into();
for (i, _ch) in source.char_indices() {
#[allow(clippy::cast_possible_truncation)]
builder.add_source_mapping(&output, i as u32, None);
assert!(
builder.generated_line == line && builder.generated_column == column,
"Incorrect generated mapping for '{source}' ({:?}) starting at {i} - line {}, column {}",
source.as_bytes(),
builder.generated_line,
builder.generated_column
);
assert_eq!(builder.last_generated_update, source.len());
}
}
create_mappings("", 0, 0);
create_mappings("abc", 0, 3);
create_mappings("\n", 1, 0);
create_mappings("\n\n\n", 3, 0);
create_mappings("\r", 1, 0);
create_mappings("\r\r\r", 3, 0);
create_mappings("\r\n", 1, 0);
create_mappings("\r\n\r\n\r\n", 3, 0);
create_mappings("\nabc", 1, 3);
create_mappings("abc\n", 1, 0);
create_mappings("\rabc", 1, 3);
create_mappings("abc\r", 1, 0);
create_mappings("\r\nabc", 1, 3);
create_mappings("abc\r\n", 1, 0);
create_mappings("ÖÖ\nÖ\nÖÖÖ", 2, 3);
}
}