[FIXED] How to downgrade or install a specific version of Composer?

Issue

I'm getting the following error in a project I'm setting up:

You are using Composer 2, which some of your plugins seem to be incompatible with. Make sure you update your plugins or report a plugin-issue to ask them to support Composer 2.

I've started at a new company this week, just trying to get their projects installed and there doesn't seem to be a way to change my composer version on Windows. I'd rather not update all their packages as I'm not familiar with the projects yet and have no clue what kind of implications go into that.

Solution

Assuming a regular composer installation, to rollback to version 1 of composer, you simply execute:

composer self-update --1

When you want to go back to version 2 (which you should, after updating or removing the incompatible plugins):

composer self-update --2

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The above will take you to the latest on any of the two major versions.

You can also "update" to a specific version just by passing the version number to self-update:

composer self-update 1.10.12
composer self-update 2.0.7

After performing any self-update, you can specify --rollback to go back to the previously installed version.

composer self-update
composer self-update --rollback

Finally, if you are feeling adventurous, you can update to a pre-release version by executing:

composer self-update --preview

Answered By - yivi

Answer Checked By - Gilberto Lyons (PHPFixing Admin)