README.md

jj-diff

Diff engine behind JayJay, a native GUI for Jujutsu. It turns two versions of a file into display-ready lines: histogram line matching, word-level changes, tree-sitter syntax spans, collapsed context, side-by-side pairing, and soft wrapping. It has no dependency on jj-lib or any UI toolkit.

Usage

use jj_diff::{build_side_by_side_rows, collapse_context_with_mapping, compute_file_diff_full};

let old = "fn main() {\n    println!(\"hello\");\n}\n";
let new = "fn main() {\n    println!(\"hello, world\");\n}\n";

// Every line, with word-level and syntax spans.
let diff = compute_file_diff_full("src/main.rs", old, new, false);
assert_eq!(diff.language, "rust");

// Unchanged runs fold into separator lines; `display_to_full` maps back to the full diff.
let collapsed = collapse_context_with_mapping(&diff);

// Removed and added lines paired for a two-column view.
for row in build_side_by_side_rows(&collapsed.diff.lines) {
    let _ = (&row.old.spans, &row.new.spans, row.old.style, row.new.style);
}

Each DiffLine carries its old and new line numbers, a DiffSpanStyle (added, removed, context, separator, …), and DiffSpans that pair text with a word-diff style and a SyntaxToken. Rendering is left to the caller.

API

Item	Purpose
compute_file_diff(path, old, new, ignore_whitespace)	Diff collapsed to 3 lines of context
compute_file_diff_full / compute_file_diff_full_plain	Every line, with or without syntax highlighting
collapse_context_with_mapping(&diff)	Collapse context and keep a display → full line mapping
ExpandableDiff, ContextExpansionSession	Reveal collapsed context incrementally
build_side_by_side_rows(&lines)	Pair lines into SideBySideRows
wrap_diff_lines, wrap_sbs_rows	Soft-wrap unified or side-by-side lines to a column width
highlight_file, highlight_file_against_base	Syntax spans for a whole file
count_changed_lines(old, new, ignore_whitespace)	Insertion and deletion counts
change_groups, canonical_review_snapshot	Hunk grouping and stable fingerprints for review state
is_git_lfs, is_git_submodule	Placeholder detection for LFS pointers and submodules

Languages

Each grammar sits behind a lang-* feature, and all of them are on by default through all-languages. Paths without an enabled grammar diff as plain text. For a smaller build, turn off the defaults and pick the grammars you need:

jj-diff = { version = "0.1", default-features = false, features = ["lang-rust", "lang-markdown"] }

Feature	Files
lang-bash	.sh, .bash, .zsh
lang-c	.c, .h
lang-cpp	.cpp, .cc, .cxx, .hpp
lang-csharp	.cs
lang-css	.css, .scss
lang-fish	.fish
lang-go	.go
lang-html	.html, .htm
lang-java	.java
lang-javascript	.js, .cjs, .mjs, .jsx
lang-json	.json
lang-kotlin	.kt, .kts
lang-make	Makefile, .mk
lang-markdown	.md, .markdown
lang-nix	.nix
lang-php	.php, .phtml
lang-python	.py
lang-ruby	.rb
lang-rust	.rs
lang-solidity	.sol
lang-sql	.sql
lang-swift	.swift
lang-toml	.toml
lang-typescript	.ts, .tsx
lang-xml	.xml
lang-yaml	.yaml, .yml
lang-zig	.zig

License

Apache-2.0