mirror of https://github.com/Wilfred/difftastic/
142 lines
3.3 KiB
Markdown
142 lines
3.3 KiB
Markdown
# It's Difftastic!
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Difftastic is an experimental structured diff tool that compares files
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based on their syntax.
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It currently supports the following languages:
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* Clojure
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* CSS
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* Emacs Lisp
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* Go
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* JavaScript
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* JSON
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* OCaml
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* Rust
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* Scheme
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The parsing logic is based on matched delimiters, so difftastic tends
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to give best results on heavily parenthesised code (e.g. Lisps or
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JSON).
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If a file has an unrecognised extension, difftastic uses a
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line-oriented diff.
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## How It Works
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(1) Parsing.
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Difftastic treats source code as a sequence of atoms or (possibly
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nested) lists.
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Language syntax is defined in `config/syntax.toml`: you provide
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regular expressions for atoms (including comments), open delimiters,
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and close delimiters.
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This is heavily inspired by
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[Comby](https://github.com/comby-tools/comby), which handles a large
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number of languages by using a similar approach.
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(2) Diffing.
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Difftastic treats diff calculations as a graph search problem. It
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finds the minimal diff using Dijkstra's algorithm.
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This is based on the excellent
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[Autochrome](https://fazzone.github.io/autochrome.html) project.
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(3) Printing.
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Difftastic prints a side-by-side diff that fits the current
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terminal. It will try to align unchanged nodes (see screenshot above).
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## Known Problems
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Crashes. The code is underdocumented, undertested, and
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unfinished.
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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. This might be solved
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by A* search.
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Comments. Small changes can show big diffs.
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## Non-goals
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Patch files. If you want to create a patch that you can later apply,
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use `diff`. Difftastic ignores whitespace, so its output is
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lossy. (AST patching is also a hard problem.)
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## Installation
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You can install the latest tag of difftastic with Cargo:
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```
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$ cargo install difftastic
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```
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Difftastic is still under heavy development, so there's usually major
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bugfixes since the latest release. I currently recommend you check out
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the repository and compile directly:
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```
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$ cargo build --release
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```
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This will give you a binary at `./target/release/difftastic` that you
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can put in a directory on your `$PATH`.
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### Adding a parser
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Add the tree-sitter-FOO git repository as a subtree.
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```
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$ git subtree add --prefix=vendor/tree-sitter-elisp git@github.com:Wilfred/tree-sitter-elisp.git main
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```
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Update `build.rs` and `sitter.rs` to include the definitions for the
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new parser.
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## Dogfooding
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Once you've compiled `difftastic` and it's on `$PATH`, you can try
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dogfooding.
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To see the changes to the current git repo in difftastic, you can add
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the following to your `.gitconfig` and run `git difftool`.
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```
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[diff]
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tool = difftastic
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[difftool]
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prompt = false
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[difftool "difftastic"]
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cmd = difftastic "$LOCAL" "$REMOTE"
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```
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Alternatively, to run difftastic as the default diff engine for a git
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command:
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```
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$ CLICOLOR_FORCE=1 GIT_EXTERNAL_DIFF=difftastic git diff
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$ CLICOLOR_FORCE=1 GIT_EXTERNAL_DIFF=difftastic git log -p --ext-diff
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```
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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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Files in `sample_files/` are also under the MIT license unless stated
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otherwise in their header.
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## Further Reading
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The [wiki](https://github.com/Wilfred/difftastic/wiki) includes a
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thorough overview of alternative diffing techniques and tools.
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