Crate diffy

Expand description

Tools for finding and manipulating differences between files

Overview

This library is intended to be a collection of tools used to find and manipulate differences between files inspired by LibXDiff and GNU Diffutils. Version control systems like Git and Mercurial generally communicate differences between two versions of a file using a diff or patch.

The current diff implementation is based on the Myers’ diff algorithm.

UTF-8 and Non-UTF-8

This library has support for working with both utf8 and non-utf8 texts. Most of the API’s have two different variants, one for working with utf8 str texts (e.g. create_patch) and one for working with bytes [u8] which may or may not be utf8 (e.g. create_patch_bytes).

Creating a Patch

A Patch between two texts can be created by doing the following:

use diffy::create_patch;

let original = "The Way of Kings\nWords of Radiance\n";
let modified = "The Way of Kings\nWords of Radiance\nOathbringer\n";

let patch = create_patch(original, modified);

A Patch can the be output in the Unified Format either by using its Display impl or by using a PatchFormatter to output the diff with color.

// Without color
print!("{}", patch);

// With color
let f = PatchFormatter::new().with_color();
print!("{}", f.fmt_patch(&patch));

--- original
+++ modified
@@ -1,2 +1,3 @@
 The Way of Kings
 Words of Radiance
+Oathbringer

Applying a Patch

Once you have a Patch you can apply it to a base image in order to recover the new text. Each hunk will be applied to the base image in sequence. Similarly to GNU patch, this implementation can detect when line numbers specified in the patch are incorrect and will attempt to find the correct place to apply each hunk by iterating forward and backward from the given position until all context lines from a hunk match the base image.

use diffy::{apply, Patch};

let s = "\
--- a/skybreaker-ideals
+++ b/skybreaker-ideals
@@ -10,6 +10,8 @@
 First:
     Life before death,
     strength before weakness,
     journey before destination.
 Second:
-    I will put the law before all else.
+    I swear to seek justice,
+    to let it guide me,
+    until I find a more perfect Ideal.
";

let patch = Patch::from_str(s).unwrap();

let base_image = "\
First:
    Life before death,
    strength before weakness,
    journey before destination.
Second:
    I will put the law before all else.
";

let expected = "\
First:
    Life before death,
    strength before weakness,
    journey before destination.
Second:
    I swear to seek justice,
    to let it guide me,
    until I find a more perfect Ideal.
";

assert_eq!(apply(base_image, &patch).unwrap(), expected);

Performing a Three-way Merge

Two files A and B can be merged together given a common ancestor or original file O to produce a file C similarly to how diff3 performs a three-way merge.

    --- A ---
  /           \
 /             \
O               C
 \             /
  \           /
    --- B ---

If files A and B modified different regions of the original file O (or the same region in the same way) then the files can be merged without conflict.

use diffy::merge;

let original = "the final empire\nThe Well of Ascension\nThe hero of ages\n";
let a = "The Final Empire\nThe Well of Ascension\nThe Hero of Ages\n";
let b = "The Final Empire\nThe Well of Ascension\nThe hero of ages\n";
let expected = "\
The Final Empire
The Well of Ascension
The Hero of Ages
";

assert_eq!(merge(original, a, b).unwrap(), expected);

If both files A and B modified the same region of the original file O (and those modifications are different), it would result in a conflict as it is not clear which modifications should be used in the merged result.

use diffy::merge;

let original = "The Final Empire\nThe Well of Ascension\nThe hero of ages\n";
let a = "The Final Empire\nThe Well of Ascension\nThe Hero of Ages\nSecret History\n";
let b = "The Final Empire\nThe Well of Ascension\nThe hero of ages\nThe Alloy of Law\n";
let expected = "\
The Final Empire
The Well of Ascension
<<<<<<< ours
The Hero of Ages
Secret History
||||||| original
The hero of ages
=======
The hero of ages
The Alloy of Law
>>>>>>> theirs
";

assert_eq!(merge(original, a, b).unwrap_err(), expected);