cabal test slow because of lack of caching

[oberblastmeister]

Describe the bug
cabal test is slower than running cabal run tests when nothing has changed. This issue is exacerbated when using the new code generators feature, which makes cabal recompile the test suite on every invocation.

To Reproduce

Clone https://github.com/gbaz/cabal-doctest-demo.

$ cabal v2-test

Running the second time still recompiles the test suite.

$ cabal v2-test

Expected behavior
Cabal should not recompile the entire test suite when nothing has changed.

System information

• NixOS 22.05
• Cabal 3.8.1.0
• GHC 9.2.4

[Mikolaj]

Do you mean "cabal test is slower"?

[oberblastmeister]

Yeah, updated it

[Mikolaj]

cabal test slower than running cabal run tests is a separate issue and there may already be a ticket about that.

Recompilation due to code generators is a new problem, because it's a new feature. I can't repro, though, because compilation fails with

Error: cabal-3.8.1.0: Main.hs doesn't exist

[gbaz]

I suspect what is happening is the demo codegen drivers always emit new code even if it is bit-for-bit identical with old code, and that in turn triggers the rebuild -- i.e. it isn't a cabal issue, but just that the demo code is not very sophisticated. I also consider this somewhat low priority, in that it is not clear to me why someone would want to repeatedly rerun tests that are not recompiled, as they will continue to yield the same results?