Install or upgrade CiviCRM using Composer 2?

Question

Has anyone documented using Composer 2 with an install and/or upgrade of Drupal 8 + CiviCRM?

I'm getting this error:

    - civicrm/composer-downloads-plugin[v2.0.0, ..., v2.1.1] require composer-plugin-api ^1.1 -> found composer-plugin-api[2.0.0] but it does not match the constraint.
    - civicrm/civicrm-core 5.30.1 requires civicrm/composer-downloads-plugin ^2.0 -> satisfiable by civicrm/composer-downloads-plugin[v2.0.0, v2.1.0, v2.1.1].
    - Root composer.json requires civicrm/civicrm-core 5.30.1 -> satisfiable by civicrm/civicrm-core[5.30.1].

Answer 1

It should be possible to do any one of these:

• Use CiviCRM 5.31+. The error message above suggests it is using 5.30.x, which has older metadata. (Compare: 5.31's composer.json vs 5.30's composer.json)

• Stick to composer v1 for as long as you're using an older version of Civi.

  composer self-update --1
  

  In the future, after you switch to a newer version of Civi (eg 5.31+), you can continue to composer v2:

  composer self-update --2
  

• Coerce the versions. Tell composer to install a new version of composer-downloads-plugin (v3.0.0 -- which supports composer v2) and pretend like it's an old version (v2.1.99 -- which is expected in civicrm-core v5.30). Command:

  composer require 'civicrm/composer-downloads-plugin:v3.0.0 as v2.1.99'
  

  In the future, after you switch to a newer version of Civi (eg 5.31+), you should edit composer.json and remove the coerced constraint. Otherwise, you may see weird behavior.

Answer 2

Although as of today (2020-11-20) there's no official word, I can see work being done towards this, e.g.

https://github.com/civicrm/composer-downloads-plugin/releases/tag/v3.0.0