Composer's why-not and prohibits commands reveal package or platform constraints blocking a dependency version.
What It Does
Inspect dependency constraints before forcing a platform or package upgrade. Find packages preventing a platform upgrade. Preview installation work and inspect the dependency tree. Find packages preventing a platform upgrade.
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
Inspect dependency constraints before forcing a platform or package upgrade. Find packages preventing a platform upgrade.
composer why-not php 8.4
composer prohibits vendor/package 3.0Example 2: Another Case
Preview installation work and inspect the dependency tree. Find packages preventing a platform upgrade.
composer install --dry-run
composer show --tree
composer why-not php 8.4Practical Example
Update a specific dependency before checking installed advisories. Find packages preventing a platform upgrade.
composer update vendor/package --with-dependencies
composer audit
composer why-not php 8.4For production, apply the compatibility and edge-case limits described below.
Important Behavior and Edge Cases
Use the checked-in lock file for reproducible application builds.
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 the checked-in lock file for reproducible application builds. |
Key Takeaways
- Composer's why-not and prohibits commands reveal package or platform constraints blocking a dependency version.
- Use the checked-in lock file for reproducible application builds.
- 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.