"version of Cabal has changed"

[snoyberg]

I know I've reported this issue before on issues that have been closed. There may currently be an open issue on this as well, I'm not certain. This issue has not been resolved, however, and seems to be easy to trigger:

1. Install a version of cabal-install with a different Cabal-library major version than what ships with GHC
2. Run cabal install -j to do a parallel build
3. Run cabal build

This results in the error message:

cabal: You need to re-run the 'configure' command. The version of Cabal being used has changed (was Cabal-1.18.1.5, now Cabal-1.22.2.0).

>ghc --version
The Glorious Glasgow Haskell Compilation System, version 7.8.4
>ghc-pkg list Cabal
WARNING: cache is out of date: C:/Users/Michael/AppData/Local/Programs/minghc-7.8.4-i386/ghc-7.8.4\lib\package.conf.d\package.cache
Use 'ghc-pkg recache' to fix.
C:/Users/Michael/AppData/Local/Programs/minghc-7.8.4-i386/ghc-7.8.4\lib\package.conf.d:
    Cabal-1.18.1.5

C:\Users\Michael\AppData\Roaming\ghc\i386-mingw32-7.8.4\package.conf.d:
    (no packages)
>cabal --version
cabal-install version 1.22.2.0
using version 1.22.2.0 of the Cabal library

I performed this test on Windows, but it's occurred to me on Linux many times too.

[23Skidoo]

This is sort of expected behaviour (see #2438, #1938), but since it keeps causing problems, we should add a workaround. I suggest that setupWrapper should pick the external setup method even for build-type: Simple when the package is already configured and the appropriate version of Cabal is installed.

[23Skidoo]

Alternatively, we can re-run configure automatically instead of printing an error message. I believe @ttuegel was looking into making that happen.

[ttuegel]

Yes, I have a branch which automatically reconfigures whenever necessary. I just need to do some testing with newer cabal-install vs. older Cabal to be sure they integrate correctly, then I'll make a PR.

[bitemyapp]

@ttuegel it would be really lovely to see that go live, thank you! 🐻

[dcoutts]

Another fix is here #2633.

[23Skidoo]

Since #2633 has been merged, this can now be closed.