takes an extension specification equivalent to that of
`php.withExtensions`, `extraConfig` a string of additional `php.ini`
configuration parameters. For example, a PHP package with the opcache
and ImageMagick extensions enabled, and `memory_limit` set to `256M`:

```nix
php.buildEnv {
  extensions =
    { all, ... }:
    with all;
    [
      imagick
      opcache
    ];
  extraConfig = "memory_limit=256M";
}
```

#### Example setup for `phpfpm` {#ssec-php-user-guide-installing-with-extensions-phpfpm}

You can use the previous examples in a `phpfpm` pool called `foo` as
follows:

```nix
let
  myPhp = php.withExtensions (
    { all, ... }:
    with all;
    [
      imagick
      opcache
    ]
  );
in
{
  services.phpfpm.pools."foo".phpPackage = myPhp;
}
```

```nix
let
  myPhp = php.buildEnv {
    extensions =
      { all, ... }:
      with all;
      [
        imagick
        opcache
      ];
    extraConfig = "memory_limit=256M";
  };
in
{
  services.phpfpm.pools."foo".phpPackage = myPhp;
}
```

#### Example usage with `nix-shell` {#ssec-php-user-guide-installing-with-extensions-nix-shell}

This brings up a temporary environment that contains a PHP interpreter
with the extensions `imagick` and `opcache` enabled:

```sh
nix-shell -p 'php.withExtensions ({ all, ... }: with all; [ imagick opcache ])'
```

### Installing PHP packages with extensions {#ssec-php-user-guide-installing-packages-with-extensions}

All interactive tools use the PHP package you get them from, so all
packages at `php.packages.*` use the `php` package with its default
extensions. Sometimes this default set of extensions isn't enough and
you may want to extend it. A common case of this is the `composer`
package: a project may depend on certain extensions and `composer`
won't work with that project unless those extensions are loaded.

Example of building `composer` with additional extensions:

```nix
(php.withExtensions (
  { all, enabled }:
  enabled
  ++ (with all; [
    imagick
    redis
  ])
)).packages.composer
```

### Overriding PHP packages {#ssec-php-user-guide-overriding-packages}

`php-packages.nix` form a scope, allowing us to override the packages defined
within. For example, to apply a patch to a `mysqlnd` extension, you can
pass an overlay-style function to `php`’s `packageOverrides` argument:

```nix
php.override {
  packageOverrides = final: prev: {
    extensions = prev.extensions // {
      mysqlnd = prev.extensions.mysqlnd.overrideAttrs (attrs: {
        patches = attrs.patches or [ ] ++ [
          # ...
        ];
      });
    };
  };
}
```

### Building PHP projects {#ssec-building-php-projects}

With [Composer](https://getcomposer.org/), you can effectively build PHP
projects by streamlining dependency management. As the de-facto standard
dependency manager for PHP, Composer enables you to declare and manage the
libraries your project relies on, ensuring a more organized and efficient
development process.

Composer is not a package manager in the same sense as `Yum` or `Apt` are. Yes,
it deals with "packages" or libraries, but it manages them on a per-project
basis, installing them in a directory (e.g. `vendor`) inside your project. By
default, it does not install anything globally. This idea is not new and
Composer is strongly inspired by node's `npm` and ruby's `bundler`.

Currently, there is no other PHP tool that offers the same functionality as
Composer. Consequently, incorporating a helper in Nix to facilitate building
such applications is a logical choice.

In a Composer project, dependencies are defined in a `composer.json` file,
while their specific versions are locked in a `composer.lock` file. Some
Composer-based projects opt to include this `composer.lock` file in their source
code, while others choose not to.

In Nix, there are multiple approaches to building a Composer-based project.

One such method is the `php.buildComposerProject2` helper function, which serves