Assertion failed after changing the version: field in the middle of a cabal build

[andreasabel]

Maybe cabal should cache the contents of build configuration files (.cabal files, cabal.project etc) during a build so that changes to these files don't get cabal into inconsistent states.

The scenario:

1. clone https://github.com/agda/agda, checkout tag v2.7.0.1, and start cabal build
2. once GHC starts compiling the 400+ modules of the Agda library, while the build is still running (takes quite a while), change the version in Agda.cabal to e.g. 2.7.0.
3. then after the build is finished, restart cabal build
4. observe the Assertion failed; cabal is in an inconsistent state

Here is a run (with version 2.8.0.1 -> 2.8.0)

$ cabal build
...
[437 of 437] Compiling Agda.Main        ( src/full/Agda/Main.hs, /Users/abela/agda/dist-newstyle/build/aarch64-osx/ghc-9.10.1/Agda-2.8.0.1/build/Agda/Main.o, /Users/abela/agda/dist-newstyle/build/aarch64-osx/ghc-9.10.1/Agda-2.8.0.1/build/Agda/Main.dyn_o )
...
./Agda.cabal has been changed. Re-configuring with most recently used options.
If this fails, please run configure manually.
Configuring library for Agda-2.8.0...
Configuring executable 'agda' for Agda-2.8.0...
Preprocessing executable 'agda' for Agda-2.8.0...
Building executable 'agda' for Agda-2.8.0...
[1 of 1] Compiling Main             ( src/main/Main.hs, /Users/abela/agda/dist-newstyle/build/aarch64-osx/ghc-9.10.1/Agda-2.8.0.1/x/agda/build/agda/agda-tmp/Main.o )
[2 of 2] Linking /Users/abela/agda/dist-newstyle/build/aarch64-osx/ghc-9.10.1/Agda-2.8.0.1/x/agda/build/agda/agda
...
$  cabal build                                                                                      ✔ │ 5m 19s │ 18:05:41 
Resolving dependencies...
Build profile: -w ghc-9.10.1 -O1
In order, the following will be built (use -v for more details):
 - Agda-2.8.0.1 (lib) (configuration changed)
 - Agda-2.8.0.1 (exe:agda-mode) (configuration changed)
 - Agda-2.8.0.1 (exe:agda) (configuration changed)
Configuring executable 'agda-mode' for Agda-2.8.0.1...
Configuring library for Agda-2.8.0.1...
Preprocessing executable 'agda-mode' for Agda-2.8.0.1...
Building executable 'agda-mode' for Agda-2.8.0.1...
Preprocessing library for Agda-2.8.0.1...
Building library for Agda-2.8.0.1...
...
[8 of 8] Linking /Users/abela/agda/dist-newstyle/build/aarch64-osx/ghc-9.10.1/Agda-2.8.0.1/x/agda-mode/build/agda-mode/agda-mode [Objects changed]
...
[152 of 437] Compiling Agda.Setup       ( src/setup/Agda/Setup.hs, /Users/abela/agda/dist-newstyle/build/aarch64-osx/ghc-9.10.1/Agda-2.8.0.1/build/Agda/Setup.o, /Users/abela/agda/dist-newstyle/build/aarch64-osx/ghc-9.10.1/Agda-2.8.0.1/build/Agda/Setup.dyn_o ) [src/data/latex/agda.sty changed]
...
Configuring executable 'agda' for Agda-2.8.0.1...
Assertion failed
CallStack (from HasCallStack):
  assert, called at src/Distribution/Simple/PackageIndex.hs:210:30 in Cabal-3.12.1.0-inplace:Distribution.Simple.PackageIndex
  mkPackageIndex, called at src/Distribution/Simple/PackageIndex.hs:225:17 in Cabal-3.12.1.0-inplace:Distribution.Simple.PackageIndex
Error: [Cabal-7125]
Failed to build exe:agda from Agda-2.8.0.1. The failure occurred during the configure step.