Composer update fails with "drush/drush 9.6.0 requires symfony/yaml ^3.4 -> satisfiable by symfony/yaml[3.4.x-dev]"

Question

I have a custom installation of Drupal that is managed by Composer. I executed composer outdated

That displayed some outdated packages. (see below)

I picked symfony/yaml and executed composer require symfony/yaml

My question is this: How do I resolve "Problem 1" shown in the screenshot. I assumed "-> satisfiable by...symfony/yaml v4.3.0" and ran composer require symfony/yaml:v4.3.0

Still more errors... very much the same.

Answer 1

The package drush/drush requires a v3.4.x version of symfony/yaml and thefore conflicts with your request to update symfony/yaml to version 4.3.x.

There are simple solutions as drush/drush is a development tool.

1. Remove the require-dev dependency to drush/drush ...

   composer remove 'drush/drush'
   

   ... and install the drush cli globally:

   composer --global require 'drush/drush'
   

2. Even better: Use a tool like composer-bin-plugin to circumvent the dependency conflict in your global requirements:

   composer remove 'drush/drush'
   composer --global require bamarni/composer-bin-plugin
   composer --global bin drush require 'drush/drush'
   

3. Further options to install drush globally without dependency conflicts are tools like cgr or phar.io's phive.

More information about this topic can be found in composer/composer issue #5390.