Symfony 2.8升级至3.4受阻，Composer更新报错求助

Hey there, let's get this Composer issue sorted out so you can keep moving with your Symfony upgrade. That error you're seeing is actually a heads-up from Composer about how it handles root requirements vs. dependent packages. Here's what's going on and how to fix it:

What's Causing the Error? #

When you run php composer.phar update symfony/symfony --with-dependencies, Composer tries to update symfony/symfony and all the packages it depends on. But packages like symfony/polyfill-apcu and twig/twig are two things at once:

• They're dependencies of symfony/symfony
• They're also root requirements (meaning you've listed them directly in your composer.json file)

Composer won't automatically update these root-level packages unless you explicitly tell it to include them in the update command—hence the "not explicitly whitelisted, ignoring" message.

Quick Fix: Update the Whitelisted Packages #

Just add the packages mentioned in the error to your update command. For the ones you listed, run this:

php composer.phar update symfony/symfony symfony/polyfill-apcu twig/twig --with-dependencies

If you get similar warnings for other packages later, just add those to the command too.

More Robust Approach #

If you want to avoid having to list each package one by one, you can use the --update-with-all-dependencies flag instead (note the "all"). This tells Composer to update all dependencies, including root requirements that are linked to the package you're upgrading:

php composer.phar update symfony/symfony --update-with-all-dependencies

⚠️ A quick heads-up: This will update more packages than the original command, so make sure your composer.json version constraints are set correctly for Symfony 3.4 (e.g., change symfony/symfony to ^3.4 first) to avoid unexpected breaking changes.

Bonus Upgrade Tips #

Since you're moving from 2.8 to 3.4, don't forget these key steps to smooth out the process:

• First, adjust your composer.json to set Symfony's version constraint to ^3.4 before running updates
• Go through Symfony's 3.4 upgrade guidelines to fix any deprecated code in your project (like removed methods or changed configuration)
• Check that any third-party bundles you're using support Symfony 3.4—you might need to upgrade those bundles first if they're stuck on older versions

内容的提问来源于stack exchange，提问作者Tadeusz Hyzy