Dependency Management

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  1. Dependency Management in MediaWiki Extensions

Dependency management is a crucial aspect of developing and maintaining MediaWiki extensions. It ensures that your extension functions correctly by specifying and handling the required software components it relies upon. Without proper dependency management, extensions can break due to updates in MediaWiki itself or other extensions, leading to instability and user frustration. This article provides a comprehensive guide to dependency management in MediaWiki extensions, geared towards beginners.

What are Dependencies?

In the context of MediaWiki extensions, a dependency is any external component that your extension needs to function. These components can include:

  • **MediaWiki Core Versions:** Your extension might require a specific version or range of versions of MediaWiki itself. For instance, an extension using a newly introduced API might require MediaWiki 1.35 or later.
  • **Other Extensions:** Some extensions build upon the functionality provided by others. Your extension might depend on extensions like Semantic MediaWiki, VisualEditor, or REST API.
  • **PHP Libraries:** Extensions often utilize external PHP libraries for tasks like image manipulation, data parsing, or API interactions. Examples include libraries for handling JSON, XML, or complex mathematical operations.
  • **JavaScript Libraries:** For client-side functionality, extensions may rely on JavaScript libraries like jQuery, Bootstrap, or specialized charting libraries.
  • **Specific PHP Extensions:** Your PHP code might require certain PHP extensions to be installed and enabled on the server, such as `gd`, `curl`, or `intl`.

Why is Dependency Management Important?

  • **Compatibility:** Ensuring compatibility between your extension and MediaWiki, other extensions, and PHP versions is paramount. Dependency management helps avoid conflicts and ensures your extension continues to work as intended after updates.
  • **Reproducibility:** Clearly defined dependencies make it easier for others to install and use your extension. A well-defined dependency list allows users to quickly identify and install any missing components.
  • **Security:** Using well-maintained and up-to-date dependencies helps mitigate security risks. Outdated dependencies can contain vulnerabilities that attackers can exploit.
  • **Maintainability:** Proper dependency management simplifies the process of updating your extension and resolving conflicts. It provides a clear understanding of the extension's external requirements.
  • **Avoiding "Works on my machine" Syndrome:** Dependencies ensure that the extension behaves consistently across different environments.

Methods of Declaring Dependencies

MediaWiki uses a specific mechanism for declaring dependencies within an extension's `extension.json` file. This file is the central point for defining extension metadata, including dependencies.

  • **`requires` Key:** The `requires` key in `extension.json` is used to specify dependencies on other extensions. The value is an array of extension names. For example:

```json { 

 "name": "MyExtension",
 "version": "1.0",
 "requires": [
   "Semantic MediaWiki",
   "REST API"
 ]

} ```

This indicates that `MyExtension` requires both Semantic MediaWiki and REST API to be installed and enabled.

  • **`config` Key & `PHP` Key:** These keys within `extension.json` are used to specify PHP extension requirements. The `config` key allows you to set PHP configuration options, while the `PHP` key explicitly lists required PHP extensions.

```json { 

 "name": "MyExtension",
 "version": "1.0",
 "config": {
   "GDRequired": true
 },
 "PHP": {
   "gd": true,
   "curl": true,
   "intl": true
 }

} ```

This example requires the `gd`, `curl`, and `intl` PHP extensions to be enabled. The `GDRequired` setting in the `config` section might be used to check if the GD library is available and display a warning if it's not.

  • **`dependencies` Key (Composer):** For PHP libraries, MediaWiki supports integration with [Composer](https://getcomposer.org/), a dependency manager for PHP. The `dependencies` key in `extension.json` is used to declare Composer dependencies. This is the preferred method for managing PHP libraries.

```json { 

 "name": "MyExtension",
 "version": "1.0",
 "dependencies": {
   "monolog/monolog": "^2.0",
   "guzzlehttp/guzzle": "^7.0"
 }

} ```

This example declares dependencies on the `monolog/monolog` and `guzzlehttp/guzzle` libraries. Composer will automatically download and install these libraries when the extension is installed. See Manual:Extension development for more details on using Composer.

  • **`MediaWiki version` Key:** Specifies the minimum MediaWiki version required for the extension.

```json { 

 "name": "MyExtension",
 "version": "1.0",
 "MediaWiki": "1.35.0"

} ``` This means the extension will not work on MediaWiki versions older than 1.35.0.

Handling Dependencies During Installation

The MediaWiki installation process automatically checks for declared dependencies.

  • **Extension Dependencies:** When installing an extension through the Special:Extensions page or via the command line, MediaWiki will verify that all required extensions are installed and enabled. If a required extension is missing, the installation will fail and display an error message.
  • **PHP Extension Dependencies:** MediaWiki will check if the required PHP extensions are enabled. If an extension is missing, the installation will likely fail, or the extension may function incorrectly.
  • **Composer Dependencies:** If the extension uses Composer dependencies, MediaWiki will automatically run `composer install` during the installation process to download and install the required libraries. This assumes that Composer is installed on the server.

Best Practices for Dependency Management

  • **Be Specific:** Whenever possible, specify precise versions or version constraints for your dependencies. Avoid using overly broad version ranges, as this can lead to compatibility issues. Use semantic versioning (SemVer) constraints (e.g., `^2.0`, `~1.2.3`) to allow for compatible updates.
  • **Minimize Dependencies:** Only include dependencies that are absolutely necessary for your extension to function. Each dependency adds complexity and potential for conflicts.
  • **Keep Dependencies Updated:** Regularly update your dependencies to benefit from bug fixes, security patches, and new features. Use Composer to manage PHP library updates.
  • **Test Thoroughly:** After updating dependencies, thoroughly test your extension to ensure that it still works as expected.
  • **Document Dependencies:** Clearly document all dependencies in your extension's documentation. This will help users understand the extension's requirements and troubleshoot any issues.
  • **Use Composer Whenever Possible:** For PHP libraries, Composer is the recommended dependency management tool. It simplifies the process of installing, updating, and managing libraries.
  • **Consider Vendor Locking:** For production environments, consider using `composer lock` to create a `composer.lock` file. This file records the exact versions of all dependencies, ensuring consistent installations across different environments.
  • **Avoid Circular Dependencies:** Ensure your extension dependencies don't create circular relationships (A depends on B, B depends on A). This can lead to installation and runtime errors.
  • **Use a Version Control System:** Always use a version control system (like Git) to track changes to your `extension.json` file and other extension files. This allows you to easily revert to previous versions if necessary.

Advanced Considerations

  • **Conditional Dependencies:** In some cases, you might want to include a dependency only under certain conditions. For example, you might want to require a specific PHP extension only if a particular feature is enabled. This can be achieved using conditional logic in your extension's code.
  • **Dependency Conflicts:** Conflicts can arise when two or more extensions require different versions of the same dependency. MediaWiki's dependency resolution mechanism attempts to resolve these conflicts automatically, but sometimes manual intervention is required. This may involve updating dependencies or modifying your extension's code.
  • **Security Scanning:** Regularly scan your dependencies for known security vulnerabilities. Tools like [OWASP Dependency-Check](https://owasp.org/www-project-dependency-check/) can help identify vulnerable dependencies.
  • **Analyzing Dependencies:** Use tools to analyze your dependencies and identify potential issues, such as outdated libraries or licensing conflicts. [PHPStan](https://phpstan.php) can help with static analysis.

Troubleshooting Dependency Issues

  • **Check Error Logs:** The MediaWiki error logs (typically located in the `errors` directory) often contain valuable information about dependency issues.
  • **Verify PHP Extensions:** Use `php -m` to list the enabled PHP extensions. Ensure that all required extensions are listed.
  • **Run Composer Install:** If you're using Composer, try running `composer install` manually to see if any errors occur.
  • **Clear MediaWiki Cache:** Sometimes, cached data can cause dependency issues. Try clearing the MediaWiki cache.
  • **Consult Documentation:** Refer to the documentation for the dependencies themselves for troubleshooting tips.
  • **Search Online Forums:** Search online forums and communities (such as the MediaWiki forums) for solutions to similar problems.

Resources and Further Reading

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