Alto Code Diff

A modern PHP library to generate, render and apply diffs, featuring advanced algorithms, versatile rendering, and full patching support.

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Features

Advanced Diff Algorithms

• Myers Diff Algorithm (default): Fast and accurate line-by-line and word-by-word diffing (O(ND)).
• LCS Diff Algorithm: Opt-in Longest Common Subsequence engine (O(MN) time and memory) for deterministic academic use cases.
• Binary Detection: Automatic detection and rejection of binary content.

Versatile Rendering

Visualize and format diffs for any output medium:

HTML Output

ANSI Side-by-Side

Full Patching Support

• Unified Diff Parsing: Parse standard unified diff patches into objects.
• Patch Application: Apply patches to files with "fuzz" factor support.
• Multi-file Bundles: Handle complex patches affecting multiple files.

Requirements

• PHP 8.3 or higher

Installation

composer require alto/code-diff

Quick Start

Basic Diff

use Alto\Code\Diff\Diff;
use Alto\Code\Diff\Renderer\UnifiedRenderer;

$old = "line1\nline2\nline3\n";
$new = "line1\nline2 modified\nline3\n";

$result = Diff::build()->compare($old, $new);

$renderer = new UnifiedRenderer('old.txt', 'new.txt');
echo $renderer->render($result);

Output:

--- old.txt
+++ new.txt
@@ -1,3 +1,3 @@
 line1
-line2
+line2 modified
 line3

Word-Level Diff

$result = Diff::build()
    ->withWordDiff()
    ->compare($old, $new);

HTML Output

use Alto\Code\Diff\Renderer\HtmlRenderer;

$renderer = new HtmlRenderer(
    showLineNumbers: true,
    wrapLines: false,
    classPrefix: 'diff-'
);

echo $renderer->render($result);

JSON Output

use Alto\Code\Diff\Renderer\JsonRenderer;

$renderer = new JsonRenderer(prettyPrint: true);
echo $renderer->render($result);

ANSI Side-by-Side Output

use Alto\Code\Diff\Renderer\AnsiSideBySideRenderer;

$renderer = new AnsiSideBySideRenderer(
    showLineNumbers: true,
    width: 120
);

echo $renderer->render($result);

Configuration Options

Context Lines

Control how many unchanged lines to show around changes:

$result = Diff::build()
    ->contextLines(5)  // Default is 3
    ->compare($old, $new);

Ignore Whitespace

Ignore whitespace differences:

$result = Diff::build()
    ->ignoreWhitespace()
    ->compare($old, $new);

Size Limits

Set maximum input size (default 5MB):

$result = Diff::build()
    ->maxBytes(10_000_000)  // 10MB
    ->compare($old, $new);

Parsing and Applying Patches

Parse a Unified Diff

use Alto\Code\Diff\Patch\UnifiedParser;

$patch = <<<'PATCH'
--- old.txt
+++ new.txt
@@ -1,3 +1,3 @@
 line1
-line2
+line2 modified
 line3
PATCH;

$parser = new UnifiedParser();
$bundle = $parser->parse($patch);

foreach ($bundle->files() as $file) {
    echo "File: {$file->oldPath} -> {$file->newPath}\n";
    echo "Hunks: " . count($file->result->hunks()) . "\n";
}

Apply a Patch

use Alto\Code\Diff\Patch\PatchApplier;

$original = "line1\nline2\nline3\n";

$applier = new PatchApplier();
$patched = $applier->apply($original, $patch);

echo $patched;
// Output: line1\nline2 modified\nline3\n

Note: PatchApplier::apply() accepts a single-file patch. For multi-file diffs, parse the patch and call applyBundle() instead.

Apply Patch with Fuzz Factor

$applier = new PatchApplier(fuzz: 2);
$patched = $applier->apply($original, $patch);

Apply Patch to Multiple Files

use Alto\Code\Diff\Model\DiffBundle;

$files = [
    'file1.txt' => "content1\n",
    'file2.txt' => "content2\n",
];

$applier = new PatchApplier();
$patchedFiles = $applier->applyBundle($files, $bundle);

Emitting Unified Diffs

From DiffResult

use Alto\Code\Diff\Patch\UnifiedEmitter;

$result = Diff::build()->compare($old, $new);

$emitter = new UnifiedEmitter();
$patch = $emitter->emit($result);

From DiffBundle

use Alto\Code\Diff\Model\DiffBundle;
use Alto\Code\Diff\Model\DiffFile;

$files = [
    new DiffFile('file1.txt', 'file1.txt', $result1),
    new DiffFile('file2.txt', 'file2.txt', $result2),
];

$bundle = new DiffBundle($files);
$emitter = new UnifiedEmitter();
$patch = $emitter->emit($bundle);

Renderer Options

UnifiedRenderer

new UnifiedRenderer(
    oldLabel: 'a/file.txt',  // Label for old version
    newLabel: 'b/file.txt'   // Label for new version
);

HtmlRenderer

new HtmlRenderer(
    showLineNumbers: true,      // Show line numbers
    wrapLines: false,           // Wrap long lines
    classPrefix: 'diff-'        // CSS class prefix
);

JsonRenderer

new JsonRenderer(
    prettyPrint: true  // Format with indentation
);

AnsiSideBySideRenderer

new AnsiSideBySideRenderer(
    showLineNumbers: true,  // Show line numbers
    width: 120              // Terminal width
);

Advanced Usage

Custom Diff Engine

You can choose between the built-in engines or implement your own.

MyersDiffEngine (Default): Uses the O(ND) Myers algorithm. Best for most use cases, especially when differences are small.

LcsDiffEngine: Uses the standard O(MN) LCS algorithm. Enable it explicitly with ->withEngine(new LcsDiffEngine()) only for small inputs, because its quadratic memory footprint is intended for controlled, academic scenarios.

use Alto\Code\Diff\Engine\LcsDiffEngine;

$result = Diff::build()
    ->withEngine(new LcsDiffEngine())
    ->compare($old, $new);

Implementing a Custom Engine

use Alto\Code\Diff\Engine\DiffEngineInterface;

class MyCustomEngine implements DiffEngineInterface
{
    public function diff(string $old, string $new, Options $opts): DiffResult
    {
        // Custom implementation
    }
}

$result = Diff::build()
    ->withEngine(new MyCustomEngine())
    ->compare($old, $new);

Working with Git Patches

The library supports parsing git-style unified diffs with headers:

$patch = <<<'PATCH'
diff --git a/file.txt b/file.txt
index abcdef..123456 100644
--- a/file.txt
+++ b/file.txt
@@ -1,3 +1,3 @@
 line1
-line2
+line2 modified
 line3
PATCH;

$parser = new UnifiedParser();
$bundle = $parser->parse($patch);

// Access headers
$file = $bundle->files()[0];
$file->headers['diff'];   // 'diff --git a/file.txt b/file.txt'
$file->headers['index'];  // 'index abcdef..123456 100644'

Documentation

For more detailed information, please refer to the documentation in the docs/ directory:

• API Reference
• Architecture
• Basic Text Comparison
• File Comparison
• Git Integration
• Patch Operations
• Rendering Options
• Advanced Scenarios
• Examples

Testing

Run the test suite:

vendor/bin/phpunit

Run tests with coverage:

vendor/bin/phpunit --coverage-text

License

This project is licensed under the MIT License.