Extract sylius/admin-api-bundle out of Sylius Core (but keep it installed by default in existing minor releases)

[pamil]

Why?

• Two packages required by sylius/admin-api-bundle are blocking Sylius from upgrading to PHP 8.
• We're rolling out v2 of the API, for both storefront and admin usage, which are getting more and more mature.
• This bundle will be extracted as for Sylius v1.8 (so that we can still include bugfixes) and removed from the default installation in Sylius v1.10. However, it will be relatively simple to add it back to v1.10 if you're still using it - composer require and that's it.
• Admin API is not as widely used as Shop API anyway.

Reference: #12298

[pamil]

It almost works, but it requires adding COMPOSER_ROOT_VERSION=dev-master with composer update for any other branch that master (so 1.8 and 1.9 as well).

If not added, resolving dependencies fails with the following message:

  Problem 1
    - sylius/admin-api-bundle[v1.8.0, ..., v1.9.1] require sylius/core-bundle ^1.6 -> found sylius/core-bundle[v1.6.0, ..., v1.9.1] but these were not loaded, likely because it conflicts with another require.
    - Root composer.json requires sylius/admin-api-bundle ^1.8 -> satisfiable by sylius/admin-api-bundle[v1.8.0, ..., v1.9.1].

I'm looking for ideas to make it work by default without having to add this env variable; it hurts DX a lot.

[pamil]

Changing branch names helps, renaming 1.8 to 1.8.x fixes the problem, but I'm not sure how it would work out for new branches based on those. 1.8.x-anything still does not work.

[pamil]

Two more potential fixes:

• explicitly specifying version in composer.json (prone to human error while tagging)
• replacing packages for the whole minor version, like 1.8.*, instead of self.version (but then eg. sylius/sylius v1.8.15 could be installed even if sylius/core-bundle v1.8.20 is required and some dependency prevents from installing more recent version of sylius/sylius)

[pamil]

I guess I'll go with explicitly setting version in composer.json, we already do that in Kernel for Sylius version - it seems like the best possible solution.

[pamil]

When upmerging, make sure all AdminApiBundle files are removed and the required version is bumped to ~1.9.0 for Sylius 1.9 and ^1.10 for Sylius 1.10 (dev-master).

The most important thing - make sure versions in composer.json are updated properly and are the same as the ones specified in the Kernel class from CoreBundle. Double-check before tagging any release.

Things have changed A LOT since that review

[lchrusciel]

Where is it used?