Support ghc 9.0 (and newer)

[blackgnezdo]

Describe the bug

There doesn't seem to be a viable plan for building the current HEAD (69dbf54) with ghc-9.0.1.

To Reproduce
Steps to reproduce the behavior:

$ cabal v2-build cabal-install --minimize-conflict-set
cabal: Could not resolve dependencies:
[__0] trying: cabal-install-3.7.0.0 (user goal)
[__1] rejecting: cabal-install:!test (constraint from config file, command
line flag, or user target requires opposite flag selection)
[__1] trying: cabal-install:*test
[__2] next goal: network-uri (dependency of cabal-install)
[__2] rejecting: network-uri-2.6.4.1, network-uri-2.6.4.0 (conflict:
cabal-install *test => network-uri>=2.6.2.0 && <2.6.4.0)
[__2] trying: network-uri-2.6.3.0
[__3] next goal: template-haskell (dependency of network-uri)
[__3] rejecting: template-haskell-2.17.0.0/installed-2.17.0.0 (conflict:
network-uri => base>=3 && <4.15, template-haskell =>
base==4.15.0.0/installed-4.15.0.0)
[__3] rejecting: template-haskell-2.17.0.0, template-haskell-2.16.0.0,
template-haskell-2.15.0.0, template-haskell-2.14.0.0,
template-haskell-2.13.0.0, template-haskell-2.12.0.0,
template-haskell-2.11.1.0, template-haskell-2.11.0.0,
template-haskell-2.10.0.0, template-haskell-2.9.0.0, template-haskell-2.8.0.0,
template-haskell-2.7.0.0, template-haskell-2.6.0.0, template-haskell-2.5.0.0,
template-haskell-2.4.0.1, template-haskell-2.4.0.0, template-haskell-2.3.0.1,
template-haskell-2.3.0.0, template-haskell-2.2.0.0 (constraint from
non-upgradeable package requires installed instance)
[__3] fail (backjumping, conflict set: network-uri, template-haskell)
After searching the rest of the dependency tree exhaustively, these were the
goals I've had most trouble fulfilling: cabal-install, template-haskell,
network-uri, cabal-install:test
$ ghc --version                                                                                                                                      
The Glorious Glasgow Haskell Compilation System, version 9.0.1
% cabal --version
cabal-install version 3.4.0.0
compiled using version 3.4.0.0 of the Cabal library 
% git log -n1   
commit 69dbf5415e341616999fcd1ddb97234ab6793aa9 (HEAD -> master, origin/master, origin/HEAD)
Merge: 69f62284b f07c922b7
Author: mergify[bot] <37929162+mergify[bot]@users.noreply.github.com>
Date:   Tue Oct 12 07:28:09 2021 +0000

    Merge pull request #7743 from peterbecich/type-annotations
    
    Type annotations

Expected behavior
Executable, viable build plan and a functional cabal-install at the end.

System information

• OpenBSD
• cabal 3.4.0.0, ghc 9.0.1

[Mikolaj]

Thank you for the test. It seems the allow-newer entries in cabal.project needs to be updated. Have you filed a ticket to network-uri to update to GHC 9? BTW GHC 9 is not yet ready for consumption and not included in ghcup nor stack.

[Mikolaj]

From what I hear from wise sages, the major work to support 9.0 is in hackage-security (bumps, release, adding GHC-9.0 CI job and handling the fallout, if any; I think I can do this part), then network-uri needs to be looked into and then cabal-install CI set up and any fallout handled there. Volunteers are welcome.

[phadej]

https://hackage.haskell.org/package/network-uri-2.6.4.1 is GHC-9.0 compatible release. cabal-install has strict bounds on network-uri in tests, because it defines orphan instances (in unlikely, but possible case that network-uri would provide Arbitrary instances directly).

[Mikolaj]

Oh, and #7763 is a serious issue, but probably just being fixed. [Edit: but apparently, while the fix works on Windows, there are related issues on Linux.]

[arrowd]

I guess, the blocked: upstream label can be removed now that network-uri was updated? The only problem left is #7763 ?