Ecosystem Upgrade: Composer Plugin Readiness for 2.0

[Seldaek]

Update September: See the list of plugins still lacking support below if you want to help

As we are getting Composer 2.0 closer and closer to a stable release,
and would like to get more people involved with testing it, it is
quite important to get the most common plugins to support our 2.0
branch. Otherwise many users will not be able to try the latest
Composer snapshots when we switch them to 2.0.

If you maintain a Composer plugin and would like to help, here is how:

• Get a composer 2.0 build by running composer self-update --snapshot

• Set up a trial project requiring your plugin from a local path repo
  so you can easily work on it and iterate, e.g.

    "repositories": [
        {"type":"path", "url": "../../my-plugin"}
    ],

• Change your plugin's composer.json to require "composer-plugin-api": "^1.0 || ^2.0" (to begin with, adjust to ^2.0 only if you can't make this work)

• Update your main plugin entry point class to implement the new
  PluginInterface methods, see e.g.
  composer/installers@d2a9832#diff-e236c450b11f27e4bb81a5069bc619bc

• Check out the UPGRADE guide for any other changes which might be relevant to you.

• Run php composer.phar update in that trial project to play with
  your plugin using Composer 2, and fix any issues you run into. If you require other plugins which are not compatible yet, you can bypass that using --ignore-platform-reqs as it will ignore the invalid composer-plugin-api requirements.

• If at all possible, releasing a version which supports both
  composer-plugin-api ^1.0 and ^2.0 is the best option really as that
  will allow people to use whichever composer version within a project,
  and makes the transition smoother. I am sure the more involved plugins
  will not be able to do this but I think for most it should be
  possible.

• Finally, report issues to us at
  https://github.com/composer/composer/issues if anything is broken or
  unclear, we'll try to help out ASAP.

Thanks for your attention and help getting the Composer v2 ecosystem up to speed!

[jrfnl]

@Seldaek Suggestion: make this a "pinned" issue ;-)

[Seldaek]

Published an UPGRADE guide now which might help. I think it covers most relevant changes, but we did change more than that for sure in internal classes.

[greg-1-anderson]

drupal/core-composer-scaffold and drupal/core-vendor-hardening only need Composer 1 for testing. We can't go up to Composer here until we also bump composer/semver in Drupal core. These plugins work with Composer 2, though, so this should not be an issue.

drupal-composer/drupal-scaffold is deprecated; everyone should switch to drupal/core-composer-scaffold. Note that it is possible to use drupal/core-composer-scaffold from Drupal ^8.9 to install really old versions of Drupal 8, back to Drupal 8.1.0 should work, although technically only 8.7.0+ is supported.

I've got one more plugin from that list that I can update to Composer 2 shortly.

[mcaskill]

Hi,

I think UPGRADE-2.0.md should explain how locking/updating/installing has changed in Composer 2.
I've noticed across a few plugins that developers not fully aware of the rather drastic change in how Composer operates. Roughly speaking:

• Composer v1: Composer resolves dependencies (dispatching *_DEPENDENCIES_SOLVING), iterates packages (while dispatching PRE_PACKAGE_* before PRE_FILE_DOWNLOAD), then finally writes the lock file.
• Composer v2: Composer resolves dependencies (dispatching PRE_POOL_CREATE), writes the lock file, dispatches PRE_OPERATIONS_EXEC, downloads the packages (while dispatching PRE_FILE_DOWNLOAD), then iterates packages (while dispatching PRE_PACKAGE_*).

In particular, people are assuming that PRE_OPERATIONS_EXEC is a replacement for PRE_DEPENDENCIES_SOLVING since they are dispatched in a similar-looking routine. The closest event to the latter would actually be PRE_POOL_CREATE.

Thanks,

---

[2020-09-28] I've updated my breakdown to include the new events in v2.

[Seldaek]

@mcaskill good point thanks, I added detailed notes and a debug mode for events in 3c25d18

[Seldaek]

Closing here as Composer 2.0 is out, not that the migration work is over but it probably never will be :)