cabal-install: base <4.22 is still non-reinstallable#12055
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GHC-9.14 ships with base-4.22, since that release of GHC, base is "reinstallable". This means that we can install a version of base that is not the one that was shipped with GHC. In #10982, we extended cabal-install to allow reinstalling base when GHC>=9.14 Yet, we should *not* allow solving for very old versions of base. Older versions of base can be picked by the solver, but they are unbuildable and give confusing error messages. To solve this, we simply also add a constraint that base must be >=4.22 if we take it to be reinstallable. So, now the error mentions that versions of base <4.22 are non-reinstallable. This is an unfortunate hack to resolve this error, but it's the best we can do. Alternatively we could try to revise old versions of base so that the solver does not pick them, but then we would still get a somewhat confusing error message (old versions of base require such and such a version of the rts), and it would require that users have a version of the Hackage tarball that is latter than the revisions. Resolves #11356
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I tested it manually using my example from #11983 (comment). Seems good, thanks. |
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(Sorry, I didn't realise that "priority: high" has an effect of bypassing two days delay before merging; I hope it's acceptable) |
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It's fine. :) |
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@mergify backport 3.18 |
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Backport #12055: cabal-install: base <4.22 is still non-reinstallable
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GHC-9.14 ships with base-4.22. Since that release of GHC, base is "reinstallable". This means that we can install a version of base that is not the one that was shipped with GHC.
In #10982, we extended cabal-install to allow reinstalling base when GHC>=9.14
Yet, we should not allow solving for very old versions of base. Older versions of base can be picked by the solver, but they are unbuildable and give confusing error messages.
We need both a version of GHC>=9.14 and a version of base>=4.22, otherwise we are forced to use the version that was shipped with GHC.
To solve this, we simply also add a constraint that base must be >=4.22 if we take it to be reinstallable. So, now the error mentions that versions of base <4.22 are non-reinstallable.
This is an unfortunate hack to resolve this error, but it's the best we can do.
Alternatively we could try to revise old versions of base so that the solver does not pick them, but then we would still get a somewhat confusing error message (old versions of base require such and such a version of the rts), and it would require that users have a version of the Hackage tarball that is latter than the revisions.
Resolves #11356
I have not added a changelog entry as this just modifies the behaviour of an unreleased feature. I think the existing changelog entry is sufficient.
Include the following checklist in your PR:
significance: significantin the changelog file.Manual QA notes
base <4.22base <4.23and rebuild