I always like to be able to write property tests for my code. When that code is Template Haskell, I'm mostly interested in the behavior of the generated code. Intuitively, I'd like to be able to write things like
import Test.QuickCheck
checkLift :: (Eq a, Lift a, Show a) => a -> Property
checkLift a = $$(liftTyped a) === a
prop_myLiftWorks :: MyType -> Property
prop_myLiftWorks = checkLift
Unfortunately, the Template Haskell stage restriction makes this exact approach totally impossible. The generated splices have to be compiled separately to run. Is there some easy way to spin up a GHC instance in the test suite (or do something with the ghc package or haskell-language-server?) and throw splices at it?
Ideally, I'd want to be able to work with declaration splices as well as expression splices. For example, to write property tests for deriving-compat, I'd want to generate arbitrary datatype declarations of various sorts and then compare Template Haskell-derived instances to GHC-derived ones.
