bjoernager/rust
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Address review comments.

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This commit is contained in:
Nicholas Nethercote 2022-06-02 11:43:14 +10:00
parent 0b81d7cdc6
commit 72de7c4102
3 changed files with 70 additions and 51 deletions
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92
compiler/rustc_span/src/lib.rs
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@ -1225,37 +1225,47 @@ impl DebuggerVisualizerFile {
#[derive(Clone)]
pub enum SourceFileLines {
/// The source file lines, in decoded (random-access) form.
Lines { lines: Vec<BytePos> },
Lines(Vec<BytePos>),
/// The source file lines in difference list form. This matches the form
/// used within metadata, which saves space by exploiting the fact that the
/// lines list is sorted and individual lines are usually not that long.
///
/// We read it directly from metadata and only decode it into `Lines` form
/// when necessary. This is a significant performance win, especially for
/// small crates where very little of `std`'s metadata is used.
Diffs {
/// Position of the first line. Note that this is always encoded as a
/// `BytePos` because it is often much larger than any of the
/// differences.
line_start: BytePos,
/// The source file lines, in undecoded difference list form.
Diffs(SourceFileDiffs),
}
/// Always 1, 2, or 4. Always as small as possible, while being big
/// enough to hold the length of the longest line in the source file.
/// The 1 case is by far the most common.
bytes_per_diff: usize,
impl SourceFileLines {
pub fn is_lines(&self) -> bool {
matches!(self, SourceFileLines::Lines(_))
}
}
/// The number of diffs encoded in `raw_diffs`. Always one less than
/// the number of lines in the source file.
num_diffs: usize,
/// The source file lines in difference list form. This matches the form
/// used within metadata, which saves space by exploiting the fact that the
/// lines list is sorted and individual lines are usually not that long.
///
/// We read it directly from metadata and only decode it into `Lines` form
/// when necessary. This is a significant performance win, especially for
/// small crates where very little of `std`'s metadata is used.
#[derive(Clone)]
pub struct SourceFileDiffs {
/// Position of the first line. Note that this is always encoded as a
/// `BytePos` because it is often much larger than any of the
/// differences.
line_start: BytePos,
/// The diffs in "raw" form. Each segment of `bytes_per_diff` length
/// encodes one little-endian diff. Note that they aren't LEB128
/// encoded. This makes for much faster decoding. Besides, the
/// bytes_per_diff==1 case is by far the most common, and LEB128
/// encoding has no effect on that case.
raw_diffs: Vec<u8>,
},
/// Always 1, 2, or 4. Always as small as possible, while being big
/// enough to hold the length of the longest line in the source file.
/// The 1 case is by far the most common.
bytes_per_diff: usize,
/// The number of diffs encoded in `raw_diffs`. Always one less than
/// the number of lines in the source file.
num_diffs: usize,
/// The diffs in "raw" form. Each segment of `bytes_per_diff` length
/// encodes one little-endian diff. Note that they aren't LEB128
/// encoded. This makes for much faster decoding. Besides, the
/// bytes_per_diff==1 case is by far the most common, and LEB128
/// encoding has no effect on that case.
raw_diffs: Vec<u8>,
}
/// A single source in the [`SourceMap`].
@ -1298,6 +1308,8 @@ impl<S: Encoder> Encodable<S> for SourceFile {
s.emit_struct_field("start_pos", false, |s| self.start_pos.encode(s))?;
s.emit_struct_field("end_pos", false, |s| self.end_pos.encode(s))?;
s.emit_struct_field("lines", false, |s| {
// We are always in `Lines` form by the time we reach here.
assert!(self.lines.borrow().is_lines());
self.lines(|lines| {
// Store the length.
s.emit_u32(lines.len() as u32)?;
@ -1384,9 +1396,14 @@ impl<D: Decoder> Decodable<D> for SourceFile {
// Read the difference list.
let num_diffs = num_lines as usize - 1;
let raw_diffs = d.read_raw_bytes(bytes_per_diff * num_diffs).to_vec();
SourceFileLines::Diffs { line_start, bytes_per_diff, num_diffs, raw_diffs }
SourceFileLines::Diffs(SourceFileDiffs {
line_start,
bytes_per_diff,
num_diffs,
raw_diffs,
})
} else {
SourceFileLines::Lines { lines: vec![] }
SourceFileLines::Lines(vec![])
}
};
let multibyte_chars: Vec<MultiByteChar> = Decodable::decode(d);
@ -1448,7 +1465,7 @@ impl SourceFile {
external_src: Lock::new(ExternalSource::Unneeded),
start_pos,
end_pos: Pos::from_usize(end_pos),
lines: Lock::new(SourceFileLines::Lines { lines }),
lines: Lock::new(SourceFileLines::Lines(lines)),
multibyte_chars,
non_narrow_chars,
normalized_pos,
@ -1457,14 +1474,19 @@ impl SourceFile {
}
}
pub fn lines<F, R>(&self, mut f: F) -> R
pub fn lines<F, R>(&self, f: F) -> R
where
F: FnMut(&[BytePos]) -> R,
F: FnOnce(&[BytePos]) -> R,
{
let mut guard = self.lines.borrow_mut();
match &*guard {
SourceFileLines::Lines { lines } => f(lines),
SourceFileLines::Diffs { mut line_start, bytes_per_diff, num_diffs, raw_diffs } => {
SourceFileLines::Lines(lines) => f(lines),
SourceFileLines::Diffs(SourceFileDiffs {
mut line_start,
bytes_per_diff,
num_diffs,
raw_diffs,
}) => {
// Convert from "diffs" form to "lines" form.
let num_lines = num_diffs + 1;
let mut lines = Vec::with_capacity(num_lines);
@ -1504,7 +1526,7 @@ impl SourceFile {
_ => unreachable!(),
}
let res = f(&lines);
*guard = SourceFileLines::Lines { lines };
*guard = SourceFileLines::Lines(lines);
res
}
}