Crate ashlar_diff 

Headless text diffs for ashlar: line diffs with a cost cap, word-level changes, hunks with context and collapsible unchanged ranges, and a unified-patch parser and writer.

No dependencies, no UI; builds for wasm32-unknown-unknown. The view lives in ashlar_ui::diff_view.

use ashlar_diff::{FileDiff, LineKind};

let d = FileDiff::from_texts("a\nb\nc\n", "a\nB\nc\n").with_paths("x.txt", "x.txt");
let hunk = &d.hunks[0];
assert_eq!((hunk.old_start, hunk.old_len, hunk.new_start, hunk.new_len), (1, 3, 1, 3));
assert_eq!(hunk.lines[1].kind, LineKind::Removed);
assert_eq!(d.to_patch(), "--- a/x.txt\n+++ b/x.txt\n@@ -1,3 +1,3 @@\n a\n-b\n+B\n c\n");

Patches from git diff parse into one FileDiff per file and write back byte for byte:

let patch = "diff --git a/f b/f\nindex 1..2 100644\n--- a/f\n+++ b/f\n@@ -1 +1 @@\n-x\n+y\n";
let files = ashlar_diff::parse_patch(patch).unwrap();
assert_eq!(files[0].new_path.as_deref(), Some("f"));
assert_eq!(ashlar_diff::write_patch(&files), patch);

Structs

DiffOptions

Options for FileDiff::from_texts_with.

Edit

An edit script from the old to the new sequence.

FileDiff

The changes to one file.

Gap

An unchanged range between hunks (or before the first, or after the last), which a view shows collapsed.

Hunk

A run of changes with the context around them.

Line

One line of a hunk.

PatchError

A patch that did not parse, and where.

Enums

FileStatus

How a file changed.

LineKind

What a diff line is.

Op

One run of an edit script. Indices are 0-based positions in the old (a) and new (b) inputs.

PatchErrorKind

Why a patch did not parse.

Constants

DEFAULT_MAX_COST

The default cost cap: the largest edit distance one Myers run may reach. Its trace takes about cap² / 2 words, so the default keeps it near 4 MB.

MAX_WORD_DIFF_LINE

Lines longer than this (bytes) get no word-level emphasis.

Functions

diff_ops

Diffs two sequences. max_cost caps one Myers run (see the module docs); it is clamped to 1..=2048.

parse_patch

Parses a unified patch into one FileDiff per file, with word-level emphasis.

word_diff

The byte ranges that changed between old and new, word by word: (in old, in new). Adjacent changed tokens merge into one range. None when either line is too long, the lines are equal, or they share no word (emphasis would then cover everything and say nothing).

write_patch

Writes files as one unified patch (the inverse of parse_patch for git diff output).