Update to version 2 fails due to duplicate replaced polyfill package

[burned42]

The PR for version 2 added some polyfill packages to the replace section of the composer.json: https://github.com/symfony/flex/pull/833/files#diff-d2ab9925cad7eac58e0ff4cc0d251a937ecf49e4b6bf57f8b95aab76648a9d34R29

As per this recommendation in the polyfill repo, I have added some of those packages to the replace section of the composer.json of my project already which now results in the following error when I try to update to symfony/flex version 2:

Your requirements could not be resolved to an installable set of packages.

  Problem 1
    - my/project is present at version dev-master and cannot be modified by Composer
    - symfony/flex[v2.0.0] cannot be installed as that would require removing my/project[dev-master]. They both replace symfony/polyfill-php80 and thus cannot coexist.
    - Root composer.json requires symfony/flex ^2.0 -> satisfiable by symfony/flex[v2.0.0].

One obvious solution would be to remove the duplicate replacement from my project. But if symfony/flex would remove that package from its replace section in future, then I'd still want to keep this package marked as replaced, so I'd have to add it to my project again (and therefore would have to check the replacement section of this package regularly to notice that change).

Overall I'm not 100% sure what the intended/recommended way would be to solve this issue and I'd guess others will face the same problem, so I thought I'd just ask :)

Maybe it wasn't even intentional to add that replace section? The recommendation linked above says that "projects" should add the polyfills to their replace section and I'd consider this more of a library/package instead of a project, but that may just be my interpretation and not the intention of the recommendation.

[stof]

This recommendation is for Flex-based projects, not for packages installed as dependency.

@nicolas-grekas those should not be added in symfony/flex either.

[nicolas-grekas]

Oops, I didn't know about this behavior.
Reverted in cc9241d
I'm going to tag a release later today.

[burned42]

awesome, thanks for the quick response @stof @nicolas-grekas 👍