Cabal: Reexport all of Cabal-syntax

[bgamari]

To preserve compatibility for downstream users Cabal will reexport all
of Cabal-syntax for the time being. In the future we may deprecate these
reexports.

This requires that we bump the cabal-version of Cabal.cabal to 1.22 and
drops support for GHC < 7.10.

Closes #7974.

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• Patches conform to the coding conventions.
• Any changes that could be relevant to users have been recorded in the changelog.
• The documentation has been updated, if necessary.

Please also shortly describe how you tested your change. Bonus points for added tests!

[Mikolaj]

Thank you.

[jneira]

Minor? caveat, reexported-modules, like other backpack related features are not well supported by stack repl. That in turn supposes you could not load the package en hls using stack.
I tried to use them in the hlint plugin of hls: haskell/haskell-language-server#166 (comment)
Upstream issue still unresolved (and i guess it wont) in stack: commercialhaskell/stack#5077 (comment)
And had to fall back to PackageImports instead.

Not sure if someone would want use stack repl or load the project in hls using stack, though.

[jneira]

Reviewing other prs in hls about it seems there was a fix in hls itself about: haskell/haskell-language-server#2468 and maybe it would work. I had to test it to confirm. But still stack repl would not work.

[jneira]

We are testing Cabal the lib for several ghcs < 7.10.3 and the tests did pass (https://github.com/haskell/cabal/runs/5687246403?check_suite_focus=true). And afaiu we are using cabal head at runtime for tests 🤔

[jneira]

Ok, at build time cabal build Cabal -w D:\ghcup\ghc\7.8.4\bin\ghc --disable-tests --disable-benchmarks --project-file cabal.project.libonly fails with:

Warning: Cabal.cabal:1:22: Packages with 'cabal-version: 1.12' or later should specify a specific version of the Cabal spec of the form 'cabal-version: x.y'.
Use 'cabal-version: 1.22'.
Configuring library for Cabal-3.7.0.0..
Error: cabal: Your compiler does not support module re-exports. To use this
feature you must use GHC 7.9 or later.

[jneira]

Lgtm, reexportsi s the cleaner way and i hope the stack repl issue will not impact most cabal developer, thanks!
As we are gonna drop support for build Cabal < 8.0 and this only restricts it to < 7.10.3 i think it would be fine.
But the changelog should note it (and it should be noted in the release in a more relevant way if the next version does not drop support for ghc < 8.0, but it would be in another pr)

[Mikolaj]

We did drop the support finally, right? #8079

[jneira]

@Mikolaj thanks for the reminder, yeah, this is not reducing support over master anymore