mirror of https://github.com/Wilfred/difftastic/
109 lines
3.4 KiB
Markdown
109 lines
3.4 KiB
Markdown
# Difftastic
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A language-aware word-level diff.
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```
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$ cargo run before.js after.js
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```
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## Other Diff Techniques
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There are a bunch of other ways of diffing text files. I summarise
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them here, along with example invocations.
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### Myers' diff algorithm
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This is the default diff algorithm in GNU diff and git diff. It finds
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the longest common subsequence (LCS) and is used on a line-by-line basis.
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There's a
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[great introduction
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here](https://blog.jcoglan.com/2017/02/12/the-myers-diff-algorithm-part-1/)
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and the original paper is [An O(ND) Difference Algorithm and Its
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Variations, Myers
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1986](http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.4.6927).
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```
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# Modern diff supports colour, but see also
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# https://www.colordiff.org/
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$ diff --color=always -u sample_files/css_before.css sample_files/css_after.css
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```
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Note that GNU diff [originally used the Hunt-McIlroy
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algorithm](http://fabiensanglard.net/git_code_review/diff.php)).
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### Patience Diff
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Myer's diff has a problem with sliders:
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```diff
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if (!$smtp_server) {
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+ $smtp_server = $repo->config('sendemail.smtpserver');
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+}
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+if (!$smtp_server) {
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foreach (qw( /usr/sbin/sendmail /usr/lib/sendmail )) {
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if (-x $_) {
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$smtp_server = $_;
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```
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Instead of:
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```diff
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+if (!$smtp_server) {
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+ $smtp_server = $repo->config('sendemail.smtpserver');
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+}
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if (!$smtp_server) {
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foreach (qw( /usr/sbin/sendmail /usr/lib/sendmail )) {
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if (-x $_) {
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```
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Git has a `--indent-heuristic` that [was added to reduce the
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likelihood of making a bad
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choice](https://github.com/git/git/commit/433860f3d0beb0c6f205290bd16cda413148f098). There's
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a [corpus of test files](https://github.com/mhagger/diff-slider-tools)
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where the ideal diff has been chosen by a human, to test different
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heuristics.
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The [patience diff
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algorithm](https://bramcohen.livejournal.com/73318.html) is an LCS
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algorithm that aims to do a better job with sliders. It produces great
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results by [doing more
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work](https://stackoverflow.com/questions/40133534/is-gits-implementation-of-the-patience-diff-algorithm-correct/40159510#40159510).
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```
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# Original behaviour
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$ git diff --no-indent-heuristic --no-index sample_files/css_before.css sample_files/css_after.css
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# As of git 2.11, this heuristic is enabled by default.
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$ git diff --indent-heuristic --no-index sample_files/css_before.css sample_files/css_after.css
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# Patience algorithm does a better a job in this example.
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$ git diff --patience --no-index sample_files/css_before.css sample_files/css_after.css
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```
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### Histogram Diff
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Git 1.7.7+ also has a [histogram
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algorithm](https://stackoverflow.com/a/32367597/509706), which aims to
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produce better results than Myers' algorithm but without [the slowdown
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of the patience algorithm](https://github.com/git/git/commit/85551232b56e763ecfcc7222e0858bac4e962c80).
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```
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# Inferior to patience on this example file.
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$ git diff --histogram --no-index sample_files/css_before.css sample_files/css_after.css
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```
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### Side-by-side Diff
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```
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$ diff -y --color=always sample_files/css_before.css sample_files/css_after.css
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```
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### Tree Diff
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Jane Street's [patdiff](https://github.com/janestreet/patdiff)
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implements a tree diff, using [an A* algorithm](https://thume.ca/2017/06/17/tree-diffing/).
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### prettydiff
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[prettydiff](https://github.com/romankoblov/prettydiff) does really
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well out of the box with the sample files here. It implements LCS on words.
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