I have just answered a question on Stackoverflow: 3rd party dependency conflict in developing Wordpress Plugin
The issue found by the developer is related to a PHP error:
Fatal error: Cannot redeclare GuzzleHttp\uri_template() (previously declared in /nas/content/staging/project/wp-content/plugins/my-plugin/vendor/guzzlehttp/guzzle/src/functions.php:17) in /nas/content/staging/project/wp-content/plugins/other-plugin/includes/lib/aws-sdk/GuzzleHttp/functions.php on line 31
To save the answer for future reference:
By design, PHP and Composer assume that you develop and distribute your code in a controlled environment. However, when you publish plugins on WordPress or modules on Joomla, you distribute the code on systems where you don't have control over what other authors install. This situation can result in name collisions such as Cannot redeclare GuzzleHttp\uri_template()...
To prepare your code for multi-vendor setups, you must prefix the PHP code to avoid name collisions or version collisions (the same library with a different version is loaded first). For instance, Guzzle is a well-known and widely used library, so if you publish a plugin including it, you must prefix it before distribution.
At first glance, you may think that prefixing only the namespaces would get the job done. But other named elements such as global functions and traits must also be prefixed to avoid all possible error types.
To prefix PHP code, there are tools or services to execute the task:
- - humbug/php-scoper. Prefixes all PHP namespaces in a file/directory to isolate the code bundled in PHARs.
- - Interfacelab/namespacer. Namespacer allows you to rename the namespace of any composer packages. It works by adding a namespace prefix to all of the namespaces. Namespacer also prefixes the package names. It then generates a folder called "lib" that you can safely include in your WordPress plugin.
- - coenjacobs/mozart. Developers tool for WordPress plugins: Wraps all your projects dependencies in your own namespace. This prevents conflicts with other plugins that load the same dependencies but in different versions.
- - PHP-Prefixer. It's an automated online service powered by a complex rule-based system to apply prefixes to Composer dependencies. In the composer.json, you just define the prefix to apply without worrying about the nitty-gritty details.
Disclaimer: I'm the lead PHP-Prefixer developer.