flickzeug

A Rust library for computing diffs, parsing and applying patches, and performing three-way merges.

Note: This is a fork of diffy maintained by prefix.dev.

Highlights

• Fuzzy patch application: Apply patches even when line numbers have drifted or context has slightly changed — essential for real-world patching scenarios
• Battle-tested: Used in production with thousands of real-world patches from conda-forge, the community-driven collection of conda packages

Features

• Diff creation: Compute differences between texts using Myers' diff algorithm, producing minimal edit sequences
• Patch parsing & formatting: Read and write unified diff format (compatible with git diff, diff -u, etc.)
• Fuzzy patch application: Apply patches with configurable fuzzy matching when line numbers don't align exactly, using similarity-based line matching
• Three-way merge: Merge changes from two sources against a common ancestor, with conflict detection and multiple conflict marker styles
• Binary support: All major APIs have *_bytes variants for working with non-UTF-8 content

Usage

Add flickzeug to your Cargo.toml:

[dependencies]
flickzeug = "0.6"

Creating a diff

use flickzeug::create_patch;

let original = "The quick brown fox\njumps over\nthe lazy dog.\n";
let modified = "The quick brown cat\njumps over\nthe sleepy dog.\n";

let patch = create_patch(original, modified);
println!("{}", patch);

Applying a patch

use flickzeug::{apply, Diff};

let original = "The quick brown fox\njumps over\nthe lazy dog.\n";
let patch_text = "\
--- a/fox
+++ b/fox
@@ -1,3 +1,3 @@
 The quick brown fox
 jumps over
-the lazy dog.
+the sleepy dog.
";

let diff = Diff::from_str(patch_text).unwrap();
let (result, stats) = apply(original, &diff).unwrap();
assert_eq!(result, "The quick brown fox\njumps over\nthe sleepy dog.\n");
assert!(stats.has_changes());

To parse a patch that touches multiple files, use patch_from_str / patch_from_bytes, which return a Vec of per-file Diffs.

Three-way merge

use flickzeug::merge;

let base = "line1\nline2\nline3\n";
let ours = "line1\nmodified by us\nline3\n";
let theirs = "line1\nline2\nline3 changed\n";

let merged = merge(base, ours, theirs).unwrap();

Command line tools

The optional cli feature builds a standalone flickzeug binary with diff, apply and merge subcommands built on the library:

cargo install flickzeug --features cli

# Print a unified diff (exit code 1 when the files differ, like GNU diff)
flickzeug diff old.txt new.txt

# Apply a (multi-file) patch with fuzzy matching; already-applied patches
# are detected and skipped
flickzeug apply changes.patch --directory ./src --fuzz 2

# Three-way merge, argument order as in `git merge-file`
flickzeug merge ours.txt base.txt theirs.txt

apply understands file creation (/dev/null), deletion, and git rename metadata, supports --reverse, --dry-run, --lenient (recount hunk headers) and -p/--strip, and exits with GNU-style status codes (0 success, 1 hunks failed, 2 trouble).

Compatibility with the reference tools is tested end-to-end (tests/compat.rs): unified diff output is byte-identical to GNU diff, merge output is byte-identical to git merge-file (merge and diff3 styles), patches cross-apply in both directions with GNU patch and git apply, and exit codes match.

Cargo features

• color (default) — colored patch formatting via nu-ansi-term (PatchFormatter::with_color). Disable with default-features = false if you only need the library.
• cli — builds the flickzeug binary described above.

License

This project is available under the terms of either the Apache 2.0 license or the MIT license.

Acknowledgments

This project is a fork of diffy by Brandon Williams. We thank the original author for their excellent work.