Difftastic is an experimental diff tool that compares files based on their syntax.

For installation instructions, see Installation in the manual.

Basic Example

In this JavaScript example, we can see:

(1) Difftastic understands nesting. It highlights the matching { and }, but understands that foo() hasn't changed despite the leading whitespace.

(2) Difftastic understands which lines should be aligned. It's aligned bar() on the left with bar(1) on the right, despite their changes.

(3) Difftastic understands that line-wrapping isn't meaningful. "eric" is now on a new line, but it hasn't changed.

One Minute Demo

This one minute screencast demonstrates difftastic usage with both standalone files and git.

Languages

Difftastic supports over 20 programming languages, see the manual for the full list.

If a file has an unrecognised extension, difftastic uses a textual diff with word highlighting.

Known Issues

Performance. Difftastic scales relatively poorly on files with a large number of changes, and can use a lot of memory.

Display. Difftastic has a side-by-side display which usually works well, but can be confusing.

Robustness. Difftastic regularly has releases that fix crashes.

Non-goals

Patching. Difftastic output is intended for human consumption, and it does not generate patches that you can apply later. Use diff if you need a patch.

(Patch files are also line-oriented, which is too limited for difftastic. Difftastic might find additions and removals on the same line, and it tracks the relationship between line numbers in the old and new file.)

Merging. AST merging is a hard problem that difftastic does not address.

FAQ

Isn't this basically --word-diff --ignore-all-space?

Word diffing can't do this.

Difftastic parses your code. It understands when whitespace matters, such as inside string literals or languages like Python. It understands that x-1 is three tokens in JS but one token in Lisp.

Can I use difftastic with git?

You can! The difftastic manual includes instructions for git usage. You can also use it with mercurial.

Does difftastic integrate with my favourite tool?

Probably not. Difftastic is young. Consider writing a plugin for your favourite tool, and I will link it in the README!

License

Difftastic is open source under the MIT license, see LICENSE for more details.

This repository also includes tree-sitter parsers by other authors in the vendor/ directory. These are a mix of the MIT license and the Apache license. See vendor/*/LICENSE for more details.

Files in sample_files/ are also under the MIT license unless stated otherwise in their header.