78 lines
3.8 KiB
Markdown
78 lines
3.8 KiB
Markdown
<!--
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tagline: Making your package depend on specific Composer versions
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-->
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# Composer platform dependencies
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## What are platform dependencies
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Composer makes information about the environment Composer runs in available as virtual packages. This allows other
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packages to define dependencies ([require](../04-schema.md#require), [conflict](../04-schema.md#conflict),
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[provide](../04-schema.md#provide), [replace](../04-schema.md#replace)) on different aspects of the platform, like PHP,
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extensions or system libraries, including version constraints.
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When you require one of the platform packages no code is installed. The version numbers of platform packages are
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derived from the environment Composer is executed in and they cannot be updated or removed. They can however be
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overwritten for the purposes of dependency resolution with a [platform configuration](../06-config.md#platform).
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**For example:** If you are executing `composer update` with a PHP interpreter in version
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`7.4.42`, then Composer automatically adds a package to the pool of available packages
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called `php` and assigns version `7.4.42` to it.
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That's how packages can add a dependency on the used PHP version:
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```json
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{
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"require": {
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"php": ">=7.4"
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}
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}
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```
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Composer will check this requirement against the currently used PHP version when running the composer command.
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### Different types of platform packages
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The following types of platform packages exist and can be depended on:
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1. PHP (`php` and the subtypes: `php-64bit`, `php-ipv6`, `php-zts` `php-debug`)
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2. PHP Extensions (`ext-*`, e.g. `ext-mbstring`)
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3. PHP Libraries (`lib-*`, e.g. `lib-curl`)
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4. Composer (`composer`, `composer-plugin-api`, `composer-runtime-api`)
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To see the complete list of platform packages available in your environment
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you can run `php composer.phar show --platform` (or `show -p` for short).
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The differences between the various Composer platform packages are explained further in this document.
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## Plugin package `composer-plugin-api`
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You can modify Composer's behavior with [plugin](plugins.md) packages. Composer provides a set of versioned APIs for
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plugins. Because internal Composer changes may **not** change the plugin APIs, the API version may not increase every
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time the Composer version increases. E.g. In Composer version `2.3.12`, the `composer-plugin-api` version could still
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be `2.2.0`.
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## Runtime package `composer-runtime-api`
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When applications which were installed with Composer are run (either on CLI or through a web request), they require the
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`vendor/autoload.php` file, typically as one of the first lines of executed code. Invocations of the Composer
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autoloader are considered the application "runtime".
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Starting with version 2.0, Composer makes [additional features](../07-runtime.md) (besides registering the class autoloader) available to the application runtime environment.
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Similar to `composer-plugin-api`, not every Composer release adds new runtime features,
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thus the version of `composer-runtime-api` is also increased independently from Composer's version.
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## Composer package `composer`
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Starting with Composer 2.2.0, a new platform package called `composer` is available, which represents the exact
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Composer version that is executed. Packages depending on this platform package can therefore depend on (or conflict
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with) individual Composer versions to cover edge cases where neither the `composer-runtime-api` version nor the
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`composer-plugin-api` was changed.
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Because this option was introduced with Composer 2.2.0, it is recommended to add a `composer-plugin-api` dependency on
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at least `>=2.2.0` to provide a more meaningful error message for users running older Composer versions.
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In general, depending on `composer-plugin-api` or `composer-runtime-api` is always recommended
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over depending on concrete Composer versions with the `composer` platform package.
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