Contributing to PHP: How to Fix Bugs in the PHP Core

This guide explains how to contribute to PHP's core by fixing bugs. We'll focus on the workflow, assuming a basic understanding of C and PHP's versioning. New feature submissions are outside the scope of this article.

Key Concepts:

• PHP's Version Lifecycle: Minor PHP versions are released yearly, with 3 years of support (2 years of active support, 1 year of security-only support). Understanding this is crucial for targeting bug fixes.
• Bug Fixing Workflow: Fixes should target the oldest supported affected version. PHP core developers will then merge the fix upwards to newer versions.
• The Bug Fixing Process: This involves: validating the bug, local reproduction, creating a test, debugging, coding the fix, committing changes, and submitting a pull request (PR).

Resolving a Bug: A Step-by-Step Example

Let's fix bug #71635 (a segfault in DatePeriod::getEndDate() when no end date is set).

1. Validation: Quickly check if the bug is reproducible using 3v4l (a tool testing code across multiple PHP versions). This helps identify affected versions.

2. Local Reproduction: Fork php/php-src, clone it, and update to the latest releases. Checkout the lowest affected, actively supported branch (e.g., php-5.6 in this case).

<code class="language-bash">git checkout -b fix-dateperiod-segfault upstream/php-5.6</code>

3. Build and Reproduce: Build PHP and run a script (e.g., segfault.php) reproducing the segfault:

<code class="language-php"><?php
$period = new DatePeriod(new DateTimeImmutable("now"), new DateInterval("P2Y4DT6H8M"), 2);
var_dump($period->getEndDate());
?></code>

<code class="language-bash">sapi/cli/php -n segfault.php</code>

4. Create a Test: Create a bug71635.phpt test file (in ext/date/tests/) to automate bug verification:

<code class="language-php">--TEST--
Bug #71635 (segfault in DatePeriod::getEndDate() when no end date has been set)
--FILE--
<?php date_default_timezone_set('UTC');
$period = new DatePeriod(new DateTimeImmutable("now"), new DateInterval("P2Y4DT6H8M"), 2);
var_dump($period->getEndDate());
?>
--EXPECT--
NULL</code>

Run the test: make test TESTS=ext/date/tests/bug71635.phpt

5. Debugging: Use a debugger (LLDB or GDB) to identify the root cause. The backtrace will pinpoint the problematic code.

6. Code the Fix: Modify the code to handle the null pointer. For example, add a check before dereferencing dpobj->end.

7. Test and Commit: Re-run the test (make test). Once successful, commit the changes.

8. Submit a PR: Submit a pull request against the appropriate branch of php/php-src.

Conclusion:

Fixing PHP core bugs is a valuable contribution requiring only basic C knowledge. It provides practical programming experience and helps improve PHP. With thousands of open bug reports, there are ample opportunities to get involved.

Frequently Asked Questions (FAQs): (These are summarized for brevity)

• Getting Started: Set up a PHP development environment, clone the source code, compile, test, and learn PHP internals.
• Reporting Bugs: Use the PHP bug tracking system, providing detailed descriptions and test cases.
• Debugging: Use Xdebug or other debugging tools.
• Common Bugs: Syntax, logic, and runtime errors; prevent them through clean code and thorough testing.
• Non-Coding Contributions: Report bugs, write/translate documentation, help with the website, participate in the community.
• Testing: Use PHPUnit for unit testing and write testable code.
• PHP Internals Mailing List: Subscribe and participate in discussions.
• Staying Updated: Use the PHP website, social media, newsletters, and communities.
• Best Practices: Meaningful names, comments, consistent style, avoid globals, error handling, input sanitization.
• Improving Skills: Practice, projects, challenges, open source contributions, books, courses, conferences.

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