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Use line-based and word-based diff when reloading and formatting buffers (#25129)

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Closes https://github.com/zed-industries/zed/issues/10122
Closes https://github.com/zed-industries/zed/issues/25034

When formatting buffers or reloading them after they change on disk, we
performed a diff between the buffer's current contents and the new
content. We need this diff in order preserve the positions of cursors
and other decorations when updating the buffer's text.

In order to handle changes within lines, we would previously compute a
*character-wise* diff. This was extremely expensive for large files.

This PR gets rid of the character-wise diff, and instead performs a
normal line-wise diff. Then, for certain replace hunks, we compute a
secondary word-based diff. Also, I've switched to the
[`imara-diff`](https://github.com/pascalkuthe/imara-diff) crate, instead
of `similar`.

Release Notes:

- Fixed a hang that could occur when large files were changed on disk or
formatted.
This commit is contained in:
Max Brunsfeld 2025-02-19 16:56:01 -08:00 • committed by GitHub
parent 1087e05da4
commit 0fdad0c0d6
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19 changed files with 429 additions and 343 deletions
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58
crates/language/src/buffer.rs
View file

@ -12,6 +12,7 @@ use crate::{
SyntaxMapMatches, SyntaxSnapshot, ToTreeSitterPoint,
},
task_context::RunnableRange,
text_diff::text_diff,
LanguageScope, Outline, OutlineConfig, RunnableCapture, RunnableTag, TextObject,
TreeSitterOptions,
};
@ -32,7 +33,6 @@ use schemars::JsonSchema;
use serde::{Deserialize, Serialize};
use serde_json::Value;
use settings::WorktreeId;
use similar::{ChangeTag, TextDiff};
use smallvec::SmallVec;
use smol::future::yield_now;
use std::{
@ -1792,61 +1792,7 @@ impl Buffer {
let old_text = old_text.to_string();
let line_ending = LineEnding::detect(&new_text);
LineEnding::normalize(&mut new_text);
let diff = TextDiff::from_chars(old_text.as_str(), new_text.as_str());
let empty: Arc<str> = Arc::default();
let mut edits = Vec::new();
let mut old_offset = 0;
let mut new_offset = 0;
let mut last_edit: Option<(Range<usize>, Range<usize>)> = None;
for change in diff.iter_all_changes().map(Some).chain([None]) {
if let Some(change) = &change {
let len = change.value().len();
match change.tag() {
ChangeTag::Equal => {
old_offset += len;
new_offset += len;
}
ChangeTag::Delete => {
let old_end_offset = old_offset + len;
if let Some((last_old_range, _)) = &mut last_edit {
last_old_range.end = old_end_offset;
} else {
last_edit =
Some((old_offset..old_end_offset, new_offset..new_offset));
}
old_offset = old_end_offset;
}
ChangeTag::Insert => {
let new_end_offset = new_offset + len;
if let Some((_, last_new_range)) = &mut last_edit {
last_new_range.end = new_end_offset;
} else {
last_edit =
Some((old_offset..old_offset, new_offset..new_end_offset));
}
new_offset = new_end_offset;
}
}
}
if let Some((old_range, new_range)) = &last_edit {
if old_offset > old_range.end
|| new_offset > new_range.end
|| change.is_none()
{
let text = if new_range.is_empty() {
empty.clone()
} else {
new_text[new_range.clone()].into()
};
edits.push((old_range.clone(), text));
last_edit.take();
}
}
}
let edits = text_diff(&old_text, &new_text);
Diff {
base_version,
line_ending,