How do I handle different PHP versions in different environments with Composer?

To handle different PHP versions across environments using Composer, set the platform config to match your target environment, lock dependencies based on the lowest supported PHP version, specify required extensions explicitly, and use aliases for edge cases. First, configure the desired PHP version in composer.json’s platform setting to ensure dependency resolution aligns with the production environment. Second, generate the composer.lock file using the oldest supported PHP version or the --prefer-lowest flag to maintain compatibility. Third, declare required PHP extensions in require to prevent installation on incompatible systems. Lastly, use repository aliases to test untagged package versions when necessary, ensuring smoother cross-environment consistency.

When you're working with PHP projects across multiple environments—like local development, staging, and production—it's common to run into differences in PHP versions. Composer can help manage dependencies despite these variations, but it requires some careful configuration.

Here’s how to handle different PHP versions effectively using Composer.

Use the platform Config Option

Composer lets you specify a "platform" version in your composer.json. This tells Composer to treat a certain PHP version as the target environment, even if the current system is running something different.

For example, if you're developing locally on PHP 8.2 but deploying to a server that runs PHP 8.1, you can set:

{
  "config": {
    "platform": {
      "php": "8.1.0"
    }
  }
}

This way, when you install or update packages, Composer will resolve dependencies based on PHP 8.1, not your local version. This helps avoid issues where a package might be compatible with your dev setup but not your production environment.

A good time to use this is when running composer install locally for deployment—especially in CI pipelines or Docker builds.

Lock Dependencies Carefully

Composer generates a composer.lock file that locks down exact versions of all dependencies. However, if you're switching PHP versions between environments, you should make sure that the lock file reflects the lowest common denominator—the oldest PHP version you support.

If you generate the lock file on a newer PHP version, some packages might choose versions that aren’t compatible with older PHP releases. To avoid that:

• Always build your lock file using the lowest supported PHP version.
• Or, use the --prefer-lowest flag carefully during testing to simulate installing with minimal versions.

You can also combine this with the platform config mentioned earlier to ensure consistent installs.

Watch Out for Platform Requirements

Some packages require specific PHP extensions or features. If your project uses different PHP versions across environments, those requirements might not always match up.

To prevent errors:

• Explicitly list required PHP extensions in your composer.json under require.
• Use conditional checks in code to gracefully handle missing features or extensions.
• Avoid relying solely on Composer’s warnings—test thoroughly in each environment.

For example:

{
  "require": {
    "php": "^7.4 || ^8.0",
    "ext-json": "*",
    "ext-pdo": "*"
  }
}

This makes sure Composer won't let you install dependencies unless those PHP versions or extensions are available.

Bonus Tip: Use Aliases for Edge Cases

If you need to test a branch or version of a package that isn’t tagged yet for your specific PHP version, consider using an alias in your composer.json.

Example:

{
  "repositories": [
    {
      "type": "vcs",
      "url": "https://github.com/your-vendor/your-package"
    }
  ],
  "require": {
    "your-vendor/your-package": "dev-main as 1.2.3"
  }
}

This can help bridge gaps when waiting for package updates that add PHP version compatibility.

Handling PHP version differences with Composer doesn’t have to be painful. With the right config and awareness of how dependency resolution works, you can keep things smooth across environments. Just remember to lock wisely, test broadly, and configure platform settings appropriately.

That’s basically it.

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