Custom module structure - Composer dependencies

[jsakars]

Having custom vendor module e.g. Acme_Demo located in app/code/Acme/Demo it's not clear how it's composer.json should be utilized.
Based on Create your component file structure - composer.json: Specifies component dependencies. For more information, see Composer integration.

Let's say Acme_Demo has a dependency on cocur/slugify - so naturally You would specify such dependency in app/code/Acme/Demo/composer.json.

Given such scenario(which is basically for all custom modules You would buy/get from custom vendors unless they put it for free on Packagist):

• custom module dependencies must be defined in it's own composer.json(how Composer is intended to be used)
• to actually get it working You would need to define the same dependencies in Your root composer.json

So the questions:

• How should custom modules composer.json be utilized?
• What is the M2 idea of Composer integration with custom modules and resolving their dependencies?

[vrann]

@werdlv that's a good question.

You are right, composer.json in the app/code/Acme/Demo is not used for the dependencies management (I'll later show explain it's needed). However when you complete the development of the module, you may decide to publish it as a composer package, let's say on Magento Marketplace or just in your local composer repository. At this point of time, composer.json will define your module as a composer package and all dependencies listed there will be used to manage dependencies of the project which uses your package.

Now, why composer.json is required before you are publishing package:

• module will not be visible in Component Manager
• ultimately every module should become a composer package, when it get re-used in different project

[jsakars]

@vrann thanks for clarification! ;)