Libraries

This chapter will tell you how to make your library installable through composer.

Every project is a package

As soon as you have a composer.json in a directory, that directory is a package. When you add a require to a project, you are making a package that depends on other packages. The only difference between your project and libraries is that your project is a package without a name.

In order to make that package installable you need to give it a name. You do this by adding a name to composer.json:

{
    "name": "acme/hello-world",
    "require": {
        "monolog/monolog": "1.0.*"
    }
}

In this case the project name is acme/hello-world, where acme is the vendor name. Supplying a vendor name is mandatory.

Note: If you don't know what to use as a vendor name, your GitHub username is usually a good bet. While package names are case insensitive, the convention is all lowercase and dashes for word separation.

Specifying the version

You need to specify the version some way. Depending on the type of repository you are using, it might be possible to omit it from composer.json, because the repository is able to infer the version from elsewhere.

If you do want to specify it explicitly, you can just add a version field:

{
    "version": "1.0.0"
}

However if you are using git, svn or hg, you don't have to specify it. Composer will detect versions as follows:

Branches

For every branch, a package development version will be created. If the branch name looks like a version, the version will be {branchname}-dev. For example a branch 2.0 will get a version 2.0-dev. If the branch does not look like a version, it will be dev-{branchname}. master results in a dev-master version.

Here are some examples of version branch names:

1.0
1.*
1.1.x
1.1.*

Note: When you install a dev version, it will install it from source. See [Repositories] for more information.

Lock file

For projects it is recommended to commit the composer.lock file into version control. For libraries this is not the case. You do not want your library to be tied to exact versions of the dependencies. It should work with any compatible version, so make sure you specify your version constraints so that they include all compatible versions.

Do not commit your library's composer.lock into version control.

If you are using git, add it to the .gitignore.

Publishing to a VCS

Once you have a vcs repository (version control system, e.g. git) containing a composer.json file, your library is already composer-installable. In this example we will publish the acme/hello-world library on GitHub under github.com/composer/hello-world.

Now, To test installing the acme/hello-world package, we create a new project locally. We will call it acme/blog. This blog will depend on acme /hello-world, which in turn depends on monolog/monolog. We can accomplish this by creating a new blog directory somewhere, containing a composer.json:

{
    "name": "acme/blog",
    "require": {
        "acme/hello-world": "dev-master"
    }
}

The name is not needed in this case, since we don't want to publish the blog as a library. It is added here to clarify which composer.json is being described.

Now we need to tell the blog app where to find the hello-world dependency. We do this by adding a package repository specification to the blog's composer.json:

{
    "name": "acme/blog",
    "repositories": {
        "acme/hello-world": {
            "vcs": { "url": "https://github.com/composer/hello-world" }
        }
    },
    "require": {
        "acme/hello-world": "dev-master"
    }
}

For more details on how package repositories work and what other types are available, see [Repositories].

That's all. You can now install the dependencies by running composer's install command!

Recap: Any git/svn/hg repository containing a composer.json can be added to your project by specifying the package repository and declaring the dependency in the require field.

Publishing to packagist

Alright, so now you can publish packages. But specifying the vcs repository every time is cumbersome. You don't want to force all your users to do that.

The other thing that you may have noticed is that we did not specify a package repository for monolog/monolog. How did that work? The answer is packagist.

Packagist is the main package repository for composer, and it is enabled by default. Anything that is published on packagist is available automatically through composer. Since monolog is on packagist, we can depend on it without having to specify any additional repositories.

Assuming we want to share hello-world with the world, we would want to publish it on packagist as well. And this is really easy.

You simply hit the big "Submit Package" button and sign up. Then you submit the URL to your VCS repository, at which point packagist will start crawling it. Once it is done, your package will be available to anyone.

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