fix(cabal-testsuite, Cabal): build the custom Setup with Cabal 3.18.1.0

[zlonast]

Fix: #12186

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[Mikolaj]

if possible, could this be done where the constructors are visible?

[zlonast]

As I understand it, we can use the new cabal-testsuite on older branches. However, Show and Read haven't been updated in those older branches, which is where the problem arises.

[zlonast]

I've added it; now we have even more CPP macros.

[philderbeast]

Is everything here needed to bump setup-depends in cabal-testsuite?

[philderbeast]

If this is extending #12348, could you add @fendor as co-author?

[zlonast]

Sorry, another force push removed the co-authorship.

[fendor]

I think my only changes are these two lines, so I don't think I deserve a co-authorship for just that 😅

[philderbeast]

This is the recurring calling pattern that #11778 adds utility functions for.

-- | The verbosity from the setup verbosity or 'normal' if the flag is not set.
setupOrNormalVerbosity :: VerbosityHandles -> CommonSetupFlags -> Verbosity
setupOrNormalVerbosity verbHandles =
  mkVerbosity verbHandles . Cabal.fromFlagOrDefault normal . setupVerbosity

I see that setupVerbosity is configVerbosity:

cabal/Cabal/src/Distribution/Simple/Setup/Config.hs

Line 255 in ac7bea9

{ setupVerbosity = configVerbosity

[zlonast]

Added

[zlonast]

Is everything here needed to bump setup-depends in cabal-testsuite?

Unfortunately, yes. cabal-testsuite's Setup.hs is not a plain custom Setup: during configure it generates the module Test.Cabal.ScriptEnv0.hs, embedding pieces of the computed LocalBuildInfo as Haskell source. The Setup itself is compiled against the external setup-depends Cabal (3.18.1.0), while the generated module is compiled against the in-tree lib:Cabal (3.19)

It is also worth noting that cabal-version: latest corresponds to 3.16.1.0, whereas we need 3.18.1.0.

Basically, our cabal-testsuite is sensitive to changes, so if we don't pin it, it will fail next time.