typeable/generic-arbitrary

Generic method implementations for Arbitrary

generic-arbitrary's Issues

Arbitrary getting stuck

I tried the following:

data Expr
    = Lit Int
    | Add Expr Expr
    | Mul Expr Expr
    deriving (Eq, Show, Generic)

instance Arbitrary Expr where
    arbitrary = genericArbitrary
    shrink = genericShrink

> generate arbitrary :: IO Expr

This usually never finishes, generating an infinitely large expression.

It did take a while to figure out that the arbitrary instance generates an infinite value rather than my other code getting stuck in an infinite loop.

I then tried using quickcheck-arbitrary-adt instead and my problem was solved. I'm not sure what the differences between the packages are.

Cheers! Yair

Please add github-repo URL to Hacakge

It's missing from https://hackage.haskell.org/package/generic-arbitrary

error `Test.QuickCheck.resize: negative size` since 0.2.1

GHCup uses generic-arbitrary: https://gitlab.haskell.org/haskell/ghcup-hs/-/blob/master/test/GHCup/ArbitraryTypes.hs

Since 0.2.1 the tests fail with:

Test suite ghcup-test: RUNNING...
FF
Failures:

  src/Test/Aeson/Internal/RoundtripSpecs.hs:59:5:
  1) GHCup.Types.JSON, JSON encoding of GHCupInfo, allows to encode values with aeson and read them back
       uncaught exception: ErrorCall
       Test.QuickCheck.resize: negative size
       CallStack (from HasCallStack):
         error, called at src/Test/QuickCheck/Gen.hs:135:22 in QuickCheck-2.14.2-a4039abb5c2bf61956f8dce1084c880ba597c6b14935be0ae502da628dbe9111:Test.QuickCheck.Gen
       (after 1 test)
         Exception thrown while showing test case:
           Test.QuickCheck.resize: negative size
           CallStack (from HasCallStack):
             error, called at src/Test/QuickCheck/Gen.hs:135:22 in QuickCheck-2.14.2-a4039abb5c2bf61956f8dce1084c880ba597c6b14935be0ae502da628dbe9111:Test.QuickCheck.Gen


  To rerun use: --match "/GHCup.Types.JSON/JSON encoding of GHCupInfo/allows to encode values with aeson and read them back/"

  src/Test/QuickCheck/Gen.hs:135:22:
  2) GHCup.Types.JSON, JSON encoding of GHCupInfo, produces the same JSON as is found in test/golden/GHCupInfo.json
       uncaught exception: ErrorCall
       Test.QuickCheck.resize: negative size
       CallStack (from HasCallStack):
         error, called at src/Test/QuickCheck/Gen.hs:135:22 in QuickCheck-2.14.2-a4039abb5c2bf61956f8dce1084c880ba597c6b14935be0ae502da628dbe9111:Test.QuickCheck.Gen

  To rerun use: --match "/GHCup.Types.JSON/JSON encoding of GHCupInfo/produces the same JSON as is found in test/golden/GHCupInfo.json/"

Randomized with seed 25004185

Finished in 0.2310 seconds
2 examples, 2 failures

I'm suspecting it may be 0e2e124

Fails to build with GHC 9.2.1

Hi,
the package failing to build with GHC 9.2.1

this package is part of dependency in ghcup test suite and it causes it to fail when building/testing with GHC 9.2.1

The Logs :-

Failed to build generic-arbitrary-0.2.0.
Build log (
/home/username/.cabal/logs/ghc-9.2.1/generic-arbitrary-0.2.0-b7ba577fe184c21dde1df651e1a01fd625359d2e2adc1e72a43a5dae766cbcf6.log
):
Warning: generic-arbitrary.cabal:18:28: Packages with 'cabal-version: 1.12' or
later should specify a specific version of the Cabal spec of the form
'cabal-version: x.y'. Use 'cabal-version: 1.22'.
Configuring library for generic-arbitrary-0.2.0..
Preprocessing library for generic-arbitrary-0.2.0..
Building library for generic-arbitrary-0.2.0..
[1 of 1] Compiling Test.QuickCheck.Arbitrary.Generic ( src/Test/QuickCheck/Arbitrary/Generic.hs, dist/build/Test/QuickCheck/Arbitrary/Generic.o, dist/build/Test/QuickCheck/Arbitrary/Generic.dyn_o )

src/Test/QuickCheck/Arbitrary/Generic.hs:53:3: error:
    • Non type-variable argument in the constraint: GArbitrary (Rep a)
      (Use FlexibleContexts to permit this)
    • In the instance declaration for ‘Arbitrary (GenericArbitrary a)’
   |
53 |   ( Generic a,
   |   ^^^^^^^^^^^^...

src/Test/QuickCheck/Arbitrary/Generic.hs:82:10: error:
    • Non type-variable argument in the constraint: KnownNat (SumLen a)
      (Use FlexibleContexts to permit this)
    • In the instance declaration for ‘GArbitrary (a :+: b)’
   |
82 | instance (GArbitrary a, GArbitrary b, KnownNat (SumLen a), KnownNat (SumLen b)
   |          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^...
cabal: Failed to build generic-arbitrary-0.2.0 (which is required by
test:ghcup-test from ghcup-0.1.17.4). See the build log above for details.

Ambiguous type compilation errors with sum types on GHC 9.4.1 and latest Hackage

With a plain sum type, on GHC 9.4.1, we get ambiguous type variable errors when trying to write instance Arbitrary X where arbitrary = genericArbitrary

Apologies for the bad issue, I'll work up a reproduction soon