Using Composer in CI Pipelines

Composer belongs in continuous integration to install reproducible project dependencies before checks and tests run.

What It Does

A CI runner installs locked packages then executes tests. Fail the pipeline early on invalid metadata or missing extensions.

Requirements and Compatibility

Use a supported PHP runtime and install any third-party tool or extension explicitly shown in the examples. Commands should be run from the project root unless stated otherwise.

Syntax, Inputs and Results

The examples separate configuration, the smallest working operation and a realistic follow-up task. Adapt file paths and dependency versions to your own project.

Example 1: Basic Use

A CI runner installs locked packages then executes tests.

name: Verify PHP
on: [push, pull_request]
jobs:
  checks:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      - uses: shivammathur/setup-php@v2
        with: {php-version: '8.4'}
      - run: composer install --no-interaction --prefer-dist
      - run: vendor/bin/phpunit

Example 2: Another Case

Fail the pipeline early on invalid metadata or missing extensions.

composer validate --strict
composer install --no-interaction --prefer-dist
composer check-platform-reqs

Practical Example

Audit dependency advisories and generate optimized autoload metadata.

composer audit --locked
composer dump-autoload --optimize

For production, apply the compatibility and edge-case limits described below.

Important Behavior and Edge Cases

Use composer install against the committed lock file, not composer update, and avoid executing untrusted package scripts in privileged jobs.

Comparison with Related Functions and Tools

Subject	Key difference
composer install vs composer update	install follows composer.lock; update resolves new versions and updates the lock file.

Common Beginner Mistakes

Mistake	Correct approach
Treating a version range as a fixed installed version	Commit composer.lock for applications and run composer install in deployment.
Skipping the prerequisite of this specific workflow	Install or configure the named tool and confirm the example can actually run.
Ignoring edge conditions	Use composer install against the committed lock file, not composer update, and avoid executing untrusted package scripts in privileged jobs.

Key Takeaways

Composer belongs in continuous integration to install reproducible project dependencies before checks and tests run.
Use composer install against the committed lock file, not composer update, and avoid executing untrusted package scripts in privileged jobs.
Keep application configuration, source code and validation tests under version control.

Use these examples as a starting point, then validate the result with the actual PHP build, dependencies and inputs used by your application.