Skip to content

diff: merge hunks separated by up to twice the context size #306

New issue

Have a question about this project? Sign up for a free GitHub account to open an issue and contact its maintainers and the community.

Sign up for GitHub

By clicking “Sign up for GitHub”, you agree to our terms of service and privacy statement. We’ll occasionally send you account related emails.

Already on GitHub? Sign in to your account

Merged
sylvestre merged 1 commit into from
Oct 18, 2026
Merged

diff: merge hunks separated by up to twice the context size #306

Show file tree
Hide file tree
Changes from all commits
Commits
Show all changes
1 commit
Select commit
File filter

Filter by extension

Filter by extension
Conversations
Failed to load comments.
Loading
Jump to
Jump to file
Failed to load files.
Loading
Diff view
Diff view
82 changes: 77 additions & 5 deletions src/context_diff.rs
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -54,7 +54,10 @@ fn make_diff(
let mut line_number_expected = 1;
let mut line_number_actual = 1;
let mut context_queue: VecDeque<&[u8]> = VecDeque::with_capacity(context_size);
let mut lines_since_mismatch = context_size + 1;
// Like GNU diff, keep changes in one hunk while at most twice the context
// size of unchanged lines separates them.
let max_gap = 2 * context_size;
let mut lines_since_mismatch = max_gap + 1;
let mut results = Vec::new();
let mut mismatch = Mismatch::new(0, 0);

Expand All @@ -80,7 +83,7 @@ fn make_diff(
for result in diff::slice(&expected_lines, &actual_lines) {
match result {
diff::Result::Left(str) => {
if lines_since_mismatch > context_size && lines_since_mismatch > 0 {
if lines_since_mismatch > max_gap {
results.push(mismatch);
mismatch = Mismatch::new(
line_number_expected - context_queue.len(),
Expand All @@ -102,7 +105,7 @@ fn make_diff(
lines_since_mismatch = 0;
}
diff::Result::Right(str) => {
if lines_since_mismatch > context_size && lines_since_mismatch > 0 {
if lines_since_mismatch > max_gap {
results.push(mismatch);
mismatch = Mismatch::new(
line_number_expected - context_queue.len(),
Expand Down Expand Up @@ -152,7 +155,7 @@ fn make_diff(
}
lines_since_mismatch = 0;
} else if line_number_actual > actual_lines_count {
if lines_since_mismatch >= context_size && lines_since_mismatch > 0 {
if lines_since_mismatch > max_gap {
results.push(mismatch);
mismatch = Mismatch::new(
line_number_expected - context_queue.len(),
Expand All @@ -168,7 +171,7 @@ fn make_diff(
mismatch.actual_missing_nl = true;
lines_since_mismatch = 0;
} else if line_number_expected > expected_lines_count {
if lines_since_mismatch >= context_size && lines_since_mismatch > 0 {
if lines_since_mismatch > max_gap {
results.push(mismatch);
mismatch = Mismatch::new(
line_number_expected - context_queue.len(),
Expand Down Expand Up @@ -800,4 +803,73 @@ mod tests {
);
assert!(nodiff_brief.is_empty());
}

#[test]
fn test_hunk_merging() {
use crate::assert_diff_eq;

let params = Params {
from: "foo".into(),
to: "bar".into(),
context_count: 1,
..Default::default()
};

// Changes separated by up to twice the context size share one hunk.
let from = ["a", "b", "c", "d", "e", "f", ""].join("\n");
let to = ["a", "B", "c", "d", "E", "f", ""].join("\n");
let expected = [
"*** foo\tTIMESTAMP",
"--- bar\tTIMESTAMP",
"***************",
"*** 1,6 ****",
" a",
"! b",
" c",
" d",
"! e",
" f",
"--- 1,6 ----",
" a",
"! B",
" c",
" d",
"! E",
" f",
"",
]
.join("\n");
let output = diff(from.as_bytes(), to.as_bytes(), &params);
assert_diff_eq!(output, expected);

// One more unchanged line between them splits the hunk.
let from = ["a", "b", "c", "d", "e", "f", "g", ""].join("\n");
let to = ["a", "B", "c", "d", "e", "F", "g", ""].join("\n");
let expected = [
"*** foo\tTIMESTAMP",
"--- bar\tTIMESTAMP",
"***************",
"*** 1,3 ****",
" a",
"! b",
" c",
"--- 1,3 ----",
" a",
"! B",
" c",
"***************",
"*** 5,7 ****",
" e",
"! f",
" g",
"--- 5,7 ----",
" e",
"! F",
" g",
"",
]
.join("\n");
let output = diff(from.as_bytes(), to.as_bytes(), &params);
assert_diff_eq!(output, expected);
}
}
68 changes: 63 additions & 5 deletions src/unified_diff.rs
View file
Open in desktop
Original file line number Diff line number Diff line change
Expand Up @@ -45,7 +45,10 @@ fn make_diff(
let mut line_number_expected = 1;
let mut line_number_actual = 1;
let mut context_queue: VecDeque<&[u8]> = VecDeque::with_capacity(context_size);
let mut lines_since_mismatch = context_size + 1;
// Like GNU diff, keep changes in one hunk while at most twice the context
// size of unchanged lines separates them.
let max_gap = 2 * context_size;
let mut lines_since_mismatch = max_gap + 1;
let mut results = Vec::new();
let mut mismatch = Mismatch::new(0, 0);

Expand All @@ -68,7 +71,7 @@ fn make_diff(
for result in diff::slice(&expected_lines, &actual_lines) {
match result {
diff::Result::Left(str) => {
if lines_since_mismatch >= context_size && lines_since_mismatch > 0 {
if lines_since_mismatch > max_gap {
results.push(mismatch);
mismatch = Mismatch::new(
line_number_expected - context_queue.len() as u32,
Expand Down Expand Up @@ -105,7 +108,7 @@ fn make_diff(
lines_since_mismatch = 0;
}
diff::Result::Right(str) => {
if lines_since_mismatch >= context_size && lines_since_mismatch > 0 {
if lines_since_mismatch > max_gap {
results.push(mismatch);
mismatch = Mismatch::new(
line_number_expected - context_queue.len() as u32,
Expand Down Expand Up @@ -142,7 +145,7 @@ fn make_diff(
}
lines_since_mismatch = 0;
} else if line_number_actual > actual_lines_count {
if lines_since_mismatch >= context_size && lines_since_mismatch > 0 {
if lines_since_mismatch > max_gap {
results.push(mismatch);
mismatch = Mismatch::new(
line_number_expected - context_queue.len() as u32,
Expand All @@ -158,7 +161,7 @@ fn make_diff(
mismatch.lines.push(DiffLine::MissingNL);
lines_since_mismatch = 0;
} else if line_number_expected > expected_lines_count {
if lines_since_mismatch >= context_size && lines_since_mismatch > 0 {
if lines_since_mismatch > max_gap {
results.push(mismatch);
mismatch = Mismatch::new(
line_number_expected - context_queue.len() as u32,
Expand Down Expand Up @@ -951,4 +954,59 @@ mod tests {
);
assert!(nodiff_brief.is_empty());
}

#[test]
fn test_hunk_merging() {
use crate::assert_diff_eq;

let params = Params {
from: "foo".into(),
to: "bar".into(),
context_count: 1,
..Default::default()
};

// Changes separated by up to twice the context size share one hunk.
let from = ["a", "b", "c", "d", "e", "f", ""].join("\n");
let to = ["a", "B", "c", "d", "E", "f", ""].join("\n");
let expected = [
"--- foo\tTIMESTAMP",
"+++ bar\tTIMESTAMP",
"@@ -1,6 +1,6 @@",
" a",
"-b",
"+B",
" c",
" d",
"-e",
"+E",
" f",
"",
]
.join("\n");
let output = diff(from.as_bytes(), to.as_bytes(), &params);
assert_diff_eq!(output, expected);

// One more unchanged line between them splits the hunk.
let from = ["a", "b", "c", "d", "e", "f", "g", ""].join("\n");
let to = ["a", "B", "c", "d", "e", "F", "g", ""].join("\n");
let expected = [
"--- foo\tTIMESTAMP",

@sylvestre sylvestre Oct 18, 2026

Copy link
Copy Markdown
Collaborator

Choose a reason for hiding this comment

The reason will be displayed to describe this comment to others. Learn more.

could you please also add the case from the issue (an insertion, so different line counts on both sides)?
in a different PR

"+++ bar\tTIMESTAMP",
"@@ -1,3 +1,3 @@",
" a",
"-b",
"+B",
" c",
"@@ -5,3 +5,3 @@",
" e",
"-f",
"+F",
" g",
"",
]
.join("\n");
let output = diff(from.as_bytes(), to.as_bytes(), &params);
assert_diff_eq!(output, expected);
}
}
Loading