Difftastic is an experimental structured diff tool that compares files based on their syntax.
Difftastic supports the following languages:
If a file has an unrecognised extension, difftastic uses a line-oriented diff.
(1) Parsing.
Difftastic uses tree-sitter for parsing. The concrete syntax tree is then converted to a sequence of atoms or (possibly nested) lists.
The command line flags --dump-ts and --dump-syntax will display
the syntax trees for a given file. Difftastic also has a simple regex-based
parser which can be enabled with the environment DFT_RX=1.
(2) Diffing.
Difftastic treats diff calculations as a graph search problem. It finds the minimal diff using Dijkstra's algorithm.
This is based on the excellent Autochrome project.
(3) Printing.
Difftastic prints a side-by-side diff that fits the current terminal. It will try to align unchanged nodes (see screenshot above).
An experimental inline diff mode is available by setting the
environment variable INLINE=1.
Robustness. Difftastic is young and each release has fixed several crashes.
Comprehensible display. Minimal diffs can be confusing: replacing one function with another may have a small amount of common punctuation even though they're completely unrelated. Alignment of slightly modified lines is a major challenge too.
Changes to long lines. Difftastic uses a side-by-side display by default, which is unhelpful if the only changes are near the end of a line.
Performance. Difftastic scales relatively poorly on files with a large number of changes, and can use a lot of memory. This might be solved by A* search.
Patch files. If you want to create a patch that you can later apply,
use diff. Difftastic ignores whitespace, so its output is
lossy. (AST patching is also a hard problem.)
You can install the latest tag of difftastic with Cargo:
$ cargo install difftastic
Difftastic is still under heavy development, so there's usually major bugfixes since the latest release. I currently recommend you check out the repository and compile directly:
$ cargo build --release
This will give you a binary at ./target/release/difftastic that you
can put in a directory on your $PATH.
Add the tree-sitter-FOO git repository as a subtree.
$ git subtree add --prefix=vendor/tree-sitter-elisp git@github.com:Wilfred/tree-sitter-elisp.git main
Add a symlink to the C source directory (Cargo will not include the
parent directory when packaging, because the parent has a Cargo.toml).
$ cd vendor
$ ln -s tree-sitter-elisp/src tree-sitter-elisp-src
Update build.rs and tree_sitter_parser.rs to include the
definitions for the new parser.
Once you've compiled difftastic and it's on $PATH, you can use it
with git commands. To see the changes to the current git repo in
difftastic, add the following to your .gitconfig and run
git difftool.
``` [diff] tool = difftastic
[difftool] prompt = false
[difftool "difftastic"] cmd = difftastic "$LOCAL" "$REMOTE" ```
Alternatively, to run difftastic as the default diff engine for a git command:
$ GIT_EXTERNAL_DIFF=difftastic git diff
$ GIT_EXTERNAL_DIFF=difftastic git log -p --ext-diff
GIT_EXTERNAL_DIFF also supports paths to binaries, so you can use
debug builds too. For example, using git show on a specific commit.
$ GIT_EXTERNAL_DIFF=/path/to/difftastic/target/debug/difftastic git show abcdef123456
Difftastic is open source under the MIT license, see LICENSE for more details.
Files in sample_files/ are also under the MIT license unless stated
otherwise in their header.
The wiki includes a thorough overview of alternative diffing techniques and tools.