mirror of https://github.com/Wilfred/difftastic/
188 lines
6.3 KiB
Markdown
188 lines
6.3 KiB
Markdown
<p align="center">
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<a href="#readme"><img src="img/logo.png" alt="it's difftastic!"/></a>
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<br>
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<a href="https://difftastic.wilfred.me.uk/introduction.html"><img src="https://img.shields.io/badge/manual-en-brightgreen?style=flat-square" alt="English manual"></a>
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<a href="https://difftastic.wilfred.me.uk/zh-CN/"><img src="https://img.shields.io/badge/manual-zh--CN-brightgreen?style=flat-square" alt="Chinese manual"></a>
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<a href="https://crates.io/crates/difftastic"><img src="https://img.shields.io/crates/v/difftastic.svg?style=flat-square" alt="crates.io"></a>
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<a href="https://codecov.io/gh/Wilfred/difftastic"><img src="https://img.shields.io/codecov/c/github/Wilfred/difftastic?style=flat-square&token=dZzAZtQT2S" alt="codecov.io"></a>
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</p>
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Difftastic is a structural diff tool that compares files based on
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their syntax.
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**For installation instructions, see
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[Installation](https://difftastic.wilfred.me.uk/installation.html) in
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[the manual](http://difftastic.wilfred.me.uk/).**
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## Basic Example
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In this JavaScript example, we can see:
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(1) Difftastic understands nesting. It highlights the matching `{` and
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`}`, but understands that `foo()` hasn't changed despite the leading
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whitespace.
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(2) Difftastic understands which lines should be aligned. It's aligned
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`bar(1)` on the left with `bar(2)` on the right, even though the
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textual content isn't identical.
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(3) Difftastic understands that line-wrapping isn't
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meaningful. `"eric"` is now on a new line, but it hasn't changed.
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## One Minute Demo
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[](https://asciinema.org/a/480875)
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This one minute screencast demonstrates difftastic usage with both
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standalone files and git.
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## Languages
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Difftastic supports over 30 programming languages, see [the
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manual](https://difftastic.wilfred.me.uk/languages_supported.html) for the full list.
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If a file has an unrecognised extension, difftastic uses a
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textual diff with word highlighting.
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## Known Issues
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Performance. Difftastic scales relatively poorly on files with a large
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number of changes, and can use a lot of memory.
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Display. Difftastic has a side-by-side display which usually works well, but can
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be confusing.
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Robustness. Difftastic regularly has releases that fix crashes.
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## Non-goals
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Patching. Difftastic output is intended for human consumption, and it
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does not generate patches that you can apply later. Use `diff` if you
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need a patch.
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(Patch files are also line-oriented, which is too limited for
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difftastic. Difftastic might find additions and removals on the same
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line, and it tracks the relationship between line numbers in the old
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and new file.)
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Merging. AST merging is a hard problem that difftastic does not
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address.
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## FAQ
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### Isn't this basically `--word-diff --ignore-all-space`?
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Word diffing [can't do
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this](https://twitter.com/_wilfredh/status/1510139929971421191/photo/1).
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Difftastic parses your code. It understands when whitespace matters,
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such as inside string literals or languages like Python. It understands
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that `x-1` is three tokens in JS but one token in Lisp.
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### Can I use difftastic with git?
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You can! The difftastic manual [includes instructions for git
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usage](https://difftastic.wilfred.me.uk/git.html). You can also use it
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[with mercurial](https://difftastic.wilfred.me.uk/mercurial.html).
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If you're a magit user, check out [this blog
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post](https://tsdh.org/posts/2022-08-01-difftastic-diffing-with-magit.html)
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showing one way to use difftastic with magit.
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### Does difftastic integrate with my favourite tool?
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Probably not. Difftastic is young. Consider writing a plugin for your
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favourite tool, and I will link it in the README!
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### Can difftastic help me with merge conflicts?
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Yes! As of version 0.50, difftastic understands merge conflict markers
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(i.e. `<<<<<<<`, `=======` and `>>>>>>>`).
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Pass your file with conflicts as a single argument to
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difftastic. Difftastic will construct the two conflicting files and
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diff those.
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```
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$ difft file_with_conflicts.js
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```
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### Can difftastic do merges?
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No. AST merging is a hard problem that difftastic does not address.
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AST diffing is a lossy process from the perspective of a text
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diff. Difftastic will ignore whitespace that isn't syntactically
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significant, but merging requires tracking whitespace.
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The [mergiraf](https://mergiraf.org/) tool does offer merges based on
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a tree-sitter AST however.
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### Can difftastic ignore reordering?
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No. Difftastic always considers order to be important, so diffing
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e.g. `set(1, 2)` and `set(2, 1)` will show changes.
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If you're diffing JSON, consider sorting the keys before passing them
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to difftastic.
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```
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$ difft <(jq --sort-keys < file_1.json) <(jq --sort-keys < file_2.json)
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```
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See also [Tricky Cases: Unordered Data
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Types](https://difftastic.wilfred.me.uk/tricky_cases.html#unordered-data-types)
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in the manual.
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### Can I use difftastic to check for syntactic changes without diffing?
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Yes. Difftastic can check if the two files have the same AST, without
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calculating a diff. This is much faster than normal diffing, and
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useful for building tools that check for changes.
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For example:
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```
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$ difft --check-only --exit-code before.js after.js
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```
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This will set the exit code to 0 if there are no syntactic changes, or
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1 if there are changes found.
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### Why aren't colours appearing in my terminal?
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Difftastic uses ANSI bright colours by default, but some terminal
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themes show bright colours as grey. Solarized is a popular theme that
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does this.
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If you're a Solarized user, use `export DFT_BACKGROUND=light` to
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disable bright colours, or try a different terminal colour scheme.
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### How does it work?
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Difftastic treats structural diffing as a graph problem, and uses
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Dijkstra's algorithm.
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My [blog
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post](https://www.wilfred.me.uk/blog/2022/09/06/difftastic-the-fantastic-diff/)
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describes the design, and there is also an [internals section in the
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manual](https://difftastic.wilfred.me.uk/diffing.html).
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## Translation
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+ [Chinese](./translation/zh-CN/README-zh-CN.md)
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## License
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Difftastic is open source under the MIT license, see LICENSE for more
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details.
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This repository also includes tree-sitter parsers by other authors in
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the `vendored_parsers/` directory. These are a mix of the MIT license and the
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Apache license. See `vendored_parsers/*/LICENSE` for more details.
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Files in `sample_files/` are also under the MIT license unless stated
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otherwise in their header.
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