Guard PackageInfo behind cabal-version: 3.10

[andreabedini]

This is a fix to ffa9f01 which introduced a new Cabal functionality without protecting it behind a new cabal-version, therefore breaking forward compatibility.

I am marking this as a draft because I have just emulated other checks without knowing how it works. That said, the example in #9331 (comment) gets be rejected.

TODOs:

• Add the above example as a test.
• Review Add PackageInfos_ (#3909) #8534 once again. Examples of dubious changes are:
  • https://github.com/haskell/cabal/pull/8534/files#diff-e7de9e3ea39b2b822f7c716a94940ed5934b74d85f30e270abffadcc7c61c4f7R1 this cabal-version is rejected now
  • https://github.com/haskell/cabal/pull/8534/files#diff-160a5ec6d22111593cbcb0b6ba2484d6615e3e0366ad986dffe7206648a24e81R1951-R1953
    cabal-version <2.2 + PackageInfo_module + default-extensions should never trigger.

Note: This adds the constructor CabalSpecV3_10 to CabalSpecVersion and is therefore a breaking change to Cabal-syntax.

Closes: #9331

[andreabedini]

Also to discuss is how to release this. As noted above it's a breaking change to Cabal-syntax. So we cannot really release it as a patch release.

[fgaz]

I think the only way is to disable the new functionality unconditionally in a patch release, then enable it conditionally in the next major release (so on cabal-version >= 3.11, not 3.10)

edit: let's discuss in #9331

[gbaz]

doesn't it make sense to keep the other check too?

[andreabedini]

AFAIK this was resolved in other PRs.