In attempting to update between major Drupal core version, for example, 8.8.X to 8.9.X using Composer, I have experienced error shown as below:
Warning from https://repo.packagist.org: Support for Composer 1 is deprecated and some packages will not be available. You should upgrade to Composer 2. See https://blog.packagist.com/deprecating-composer-1-support/ Updating dependencies (including require-dev) Your requirements could not be resolved to an installable set of packages.
To resolve this common composer issues you need to update your existing composer version to latest version as:
composer self-update --2
- Your existing composer version is older to support the latest Drupal packages/dependencies (e.g. You may need to update your composer 1 to composer 2).
- Your existing version of composer is not compatible for Drupal version.
- Your installed module doesn’t have backward compatibility for existing Composer version.