@@ -1,6 +1,14 @@
1−{- |
1+#if __GLASGOW_HASKELL__ >= 806
2+{-# OPTIONS_GHC -Wno-star-is-type #-}
3+#endif
4+#if __GLASGOW_HASKELL__ >= 800
5+{-# OPTIONS_GHC -Wno-unticked-promoted-constructors #-}
6+#endif
27
3−Generic implementation of the 'arbitrary' method. Example usage:
8+{-|
9+
10+This module is a generic implementation of the 'arbitrary' method. Example
11+usage:
412
513@
614data Foo = Foo
@@ -25,54 +33,203 @@ data Foo = Foo
2533
2634The generated 'arbitrary' method is equivalent to
2735
28−@Foo <$> arbitrary <*> arbitrary@.
36+@
37+Foo '<$>' arbitrary '<*>' arbitrary
38+@.
39+
40+It can also handle a recursive types problem. Assuming a type
41+
42+@
43+data R = R R
44+ deriving Generic
45+@
46+
47+there is no instance
48+
49+@
50+instance Arbitrary R where
51+ arbitrary = genericArbitrary
52+ shrink = genericShrink
53+@
54+
55+If you try to compile this you will get a type level error
56+
57+> • R refers to itself in all constructors
58+
59+Which means that there is no finite term for @R@ because it is recursive. But,
60+if you correct the definition of @R@ like this.
61+
62+@
63+data R = R R | F
64+ deriving Generic
65+@
66+
67+Then it will compile. And the @arbitrary@ generated will not hang forever, because
68+it respects the @size@ parameter.
69+
70+There is a limitation of recursion detection:
71+
72+@
73+data R1 = R1 R2
74+ deriving (Eq, Ord, Show, Generic)
75+ deriving anyclass NFData
76+ deriving Arbitrary via (GenericArbitrary R1)
77+
78+data R2 = R2 R1
79+ deriving (Eq, Ord, Show, Generic)
80+ deriving anyclass NFData
81+ deriving Arbitrary via (GenericArbitrary R2)
82+@
83+
84+This code will compile and the @arbitrary@ generated will always hang. Yes,
85+there is a problem with mutually recursive types.
86+
87+Now lets see an example of datatype with parameters
88+
89+@
90+data A a = A a
91+ deriving (Eq, Ord, Show)
92+ deriving anyclass NFData
93+ deriving (Generic)
94+
95+instance (Arbitrary a) => Arbitrary (A a) where
96+ arbitrary = genericArbitrary
97+ shrink = genericShrink
98+@
99+
100+It should work from first glance, but when compile it will throw an error:
101+
102+@
103+ • Could not deduce (Test.QuickCheck.Arbitrary.Generic.GArbitrary
104+ (A a)
105+ (GHC.Generics.D1
106+ ('GHC.Generics.MetaData "A" "ParametersTest" "main" 'False)
107+ (GHC.Generics.C1
108+ ('GHC.Generics.MetaCons "A" 'GHC.Generics.PrefixI 'False)
109+ (GHC.Generics.S1
110+ ('GHC.Generics.MetaSel
111+ 'Nothing
112+ 'GHC.Generics.NoSourceUnpackedness
113+ 'GHC.Generics.NoSourceStrictness
114+ 'GHC.Generics.DecidedLazy)
115+ (GHC.Generics.Rec0 a))))
116+ (TypesDiffer (A a) a))
117+ arising from a use of ‘genericArbitrary’
118+@
119+
120+Here the @TypesDiffer@ is a type familty dealing with recursive types and
121+helping us to eliminate inproper instances. To convince the compiller, that the
122+@a@ parameter is not an @A a@ we must fix the instance with additional constraint
123+
124+@
125+instance (Arg (A a) a, Arbitrary a) => Arbitrary (A a) where
126+ arbitrary = genericArbitrary
127+ shrink = genericShrink
128+@
129+
130+Now everything compiles and works as expected.
29131
30132-}
31133
32134module Test.QuickCheck.Arbitrary.Generic
33− ( GenericArbitrary(..)
135+ ( -- * Main
136+ genericArbitrary
137+#if MIN_VERSION_QuickCheck(2, 14, 0)
138+ , GenericArbitrary(..)
139+#endif
140+ , Arg
141+ -- * Internal
142+ , GArbitrary
143+ , FiniteSum
144+ , FiniteSumElem
145+ , Finite
146+ , AllFieldsFinal
147+ , TypesDiffer
148+ , ArgumentsCount
149+ , SumLen
150+ -- * Reexports
34151 , Arbitrary(..)
35− , genericArbitrary
36152 , genericShrink
37153 ) where
38154
39155import Control.Applicative
40−import Data.Coerce (coerce)
41156import Data.Proxy
42157import Data.Type.Bool
43158import GHC.Generics as G
44159import GHC.TypeLits
160+import Prelude
45161import Test.QuickCheck as QC
162+#if MIN_VERSION_QuickCheck(2, 14, 0)
163+import Data.Coerce (coerce)
46164import Test.QuickCheck.Arbitrary (GSubterms, RecursivelyShrink)
47165
166+
167+
168+-- | Newtype for @DerivingVia@
169+--
170+-- Usage:
171+--
172+-- @
173+-- data Foo = Foo
174+-- { _fooX :: X
175+-- , _fooY :: Y
176+-- } deriving (Generic)
177+-- deriving (Arbitrary) via GenericArbitrary Foo
178+-- @
179+--
180+-- @since 1.0.0
48181newtype GenericArbitrary a = GenericArbitrary { unGenericArbitrary :: a }
49182 deriving (Show, Eq)
50183
51184instance
52185 ( Generic a,
53− GArbitrary a (Rep a) 'True,
186+ GArbitrary a (Rep a) some,
54187 RecursivelyShrink (Rep a),
55188 GSubterms (Rep a) a
56189 ) => Arbitrary (GenericArbitrary a) where
57190 arbitrary = coerce (genericArbitrary :: Gen a)
58191 shrink = coerce (genericShrink :: a -> [a])
192+#endif
193+
194+-- | Constraint helper for types with parameters
195+--
196+-- Usage:
197+--
198+-- @
199+-- data A a = A a
200+-- deriving (Generic)
201+-- instance (Arg (A a) a, Arbitrary a) => Arbitrary (A a) where
202+-- arbitrary = genericArbitrary
203+-- shrink = genericShrink
204+-- @
205+--
206+-- @since 1.0.0
207+
208+type Arg self field = (TypesDiffer self field ~ 'True)
209+
210+type family TypesDiffer a b where
211+ TypesDiffer a a = 'False
212+ TypesDiffer a b = 'True
59213
60214type family AllFieldsFinal self (a :: * -> *) :: Bool where
61215 AllFieldsFinal self U1 = 'True
62216 AllFieldsFinal self (a :*: b) = AllFieldsFinal self a && AllFieldsFinal self b
63− AllFieldsFinal self (M1 S t (K1 R self)) = 'False
64− AllFieldsFinal self (M1 S t (K1 R other)) = 'True
217+ AllFieldsFinal self (M1 S t (K1 R field)) = TypesDiffer self field
65218
66219type family Finite self (a :: * -> *) :: Bool where
67220 Finite self U1 = 'True
68− Finite self (K1 R self) = 'False
69− Finite self (K1 R other) = 'True
221+ Finite self (K1 R field) = TypesDiffer self field
70222 Finite self (a :*: b) = Finite self a && Finite self b
71223 Finite self (M1 D t f) = Finite self f
72224 Finite self (a :+: b) = Finite self a || Finite self b
73225 Finite self (M1 C c f) = AllFieldsFinal self f
74226 Finite self (M1 S s f) = Finite self f
75227
228+type family ArgumentsCount (a :: * -> *) :: Nat where
229+ ArgumentsCount U1 = 1
230+ ArgumentsCount (M1 S s f) = 1
231+ ArgumentsCount (a :*: b) = (ArgumentsCount a) + (ArgumentsCount b)
232+
76233-- | Calculates count of constructors encoded by particular ':+:'.
77234-- Internal use only.
78235type family SumLen a :: Nat where
@@ -86,37 +243,40 @@ type family SumLen a :: Nat where
86243-- * a: some part of the `Rep self`
87244-- * finite: Is `a` finite? Infinite type has no finite values (like Stream)
88245class (Finite self a ~ finite) => GArbitrary self a (finite :: Bool) where
89− gArbitrary :: QC.Gen (a x)
246+ gArbitrary :: Proxy self -> QC.Gen (a x)
90247
91248instance
92− ( GArbitrary self (C1 c f) 'True
93− ) => GArbitrary self (D1 t (C1 c f)) 'True where
94− gArbitrary = M1 <$> gArbitrary @self
249+ ( GArbitrary self (M1 C c f) 'True
250+ ) => GArbitrary self (M1 D t (M1 C c f)) 'True where
251+ gArbitrary _ = M1 <$> gArbitrary (Proxy :: Proxy self)
95252
96253-- | The constructor meta information
97254instance
98255 ( GArbitrary self f some
256+ , KnownNat (ArgumentsCount f)
99257 , AllFieldsFinal self f ~ some
100− ) => GArbitrary self (C1 c f) some where
101− gArbitrary = M1 <$> scale predNat (gArbitrary @self)
258+ ) => GArbitrary self (M1 C c f) some where
259+ gArbitrary _ = M1 <$> scale predNat (gArbitrary (Proxy :: Proxy self))
102260 where
103− predNat 0 = 0
104− predNat n = pred n
261+ argumentsCount = fromIntegral $ natVal (Proxy :: Proxy (ArgumentsCount f))
262+ predNat n = max 0 $ if argumentsCount > 1
263+ then n `div` argumentsCount
264+ else pred n
105265
106266-- | Unit type instance
107267instance GArbitrary self U1 'True where
108− gArbitrary = pure U1
268+ gArbitrary _ = pure U1
109269
110270-- | Constructor field meta information
111−instance GArbitrary self f some => GArbitrary self (S1 t f) some where
112− gArbitrary = M1 <$> gArbitrary @self
271+instance GArbitrary self f some => GArbitrary self (M1 S t f) some where
272+ gArbitrary _ = M1 <$> gArbitrary (Proxy :: Proxy self)
113273
114274-- | Data of the constructor field
115275instance
116276 ( Arbitrary t
117− , Finite self (Rec0 t) ~ some
118− ) => GArbitrary self (Rec0 t) some where
119− gArbitrary = K1 <$> arbitrary
277+ , Finite self (K1 R t) ~ some
278+ ) => GArbitrary self (K1 R t) some where
279+ gArbitrary _ = K1 <$> arbitrary
120280
121281-- | Product
122282instance
@@ -124,21 +284,26 @@ instance
124284 , GArbitrary self b bf
125285 , (af && bf) ~ some
126286 ) => GArbitrary self (a :*: b) some where
127− gArbitrary = liftA2 (:*:) (gArbitrary @self) (gArbitrary @self)
287+ gArbitrary _ = liftA2 (:*:)
288+ (gArbitrary (Proxy :: Proxy self)) (gArbitrary (Proxy :: Proxy self))
128289
290+#if __GLASGOW_HASKELL__ >= 800
129291instance
130292 ( TypeError (ShowType self :<>: Text " refers to itself in all constructors")
131293 , AllFieldsFinal self f ~ 'False
132− ) => GArbitrary self (D1 t (C1 c f)) 'False where
133− gArbitrary = error "Unreachable"
294+ ) => GArbitrary self (M1 D t (M1 C c f)) 'False where
295+ gArbitrary _ = error "Unreachable"
296+#endif
134297
135298-- | ADT declaration with multiple constructors
136299instance
137300 ( FiniteSum self a b af bf
138301 , GArbitrary self (a :+: b) 'True
139− ) => GArbitrary self (D1 t (a :+: b)) 'True where
140− gArbitrary = sized $ \s -> M1 <$>
141− if s > 1 then gArbitrary @self else oneof (finiteSum @self @a @b)
302+ ) => GArbitrary self (M1 D t (a :+: b)) 'True where
303+ gArbitrary _ = sized $ \s -> M1 <$>
304+ if s > 1
305+ then gArbitrary (Proxy :: Proxy self)
306+ else oneof (finiteSum (Proxy :: Proxy self))
142307
143308-- | Any sum inside of declaration
144309instance
@@ -146,9 +311,9 @@ instance
146311 , KnownNat (SumLen a), KnownNat (SumLen b)
147312 , (af || bf) ~ some
148313 ) => GArbitrary self (a :+: b) some where
149− gArbitrary = frequency
150− [ (lfreq, G.L1 <$> gArbitrary @self)
151− , (rfreq, G.R1 <$> gArbitrary @self) ]
314+ gArbitrary _ = frequency
315+ [ (lfreq, G.L1 <$> gArbitrary (Proxy :: Proxy self))
316+ , (rfreq, G.R1 <$> gArbitrary (Proxy :: Proxy self)) ]
152317 where
153318 lfreq = fromIntegral $ natVal (Proxy :: Proxy (SumLen a))
154319 rfreq = fromIntegral $ natVal (Proxy :: Proxy (SumLen b))
@@ -156,52 +321,55 @@ instance
156321class
157322 ( Finite self a ~ af, Finite self b ~ bf
158323 ) => FiniteSum self (a :: * -> *) (b :: * -> *) af bf where
159− finiteSum :: [Gen ((a :+: b) p)]
324+ finiteSum :: Proxy self -> [Gen ((a :+: b) p)]
160325
161326instance
162327 ( FiniteSumElem self a, FiniteSumElem self b
163328 , Finite self a ~ 'True
164329 , Finite self b ~ 'True
165330 ) => FiniteSum self a b 'True 'True where
166− finiteSum = concat
167− [ fmap L1 <$> finiteElem @self @a
168− , fmap R1 <$> finiteElem @self @b]
331+ finiteSum _ = concat
332+ [ fmap L1 <$> finiteElem (Proxy :: Proxy self)
333+ , fmap R1 <$> finiteElem (Proxy :: Proxy self)]
169334
170335instance
171336 ( FiniteSumElem self a
172337 , Finite self a ~ 'True
173338 , Finite self b ~ 'False
174339 ) => FiniteSum self a b 'True 'False where
175− finiteSum = fmap L1 <$> finiteElem @self @a
340+ finiteSum _ = fmap L1 <$> finiteElem (Proxy :: Proxy self)
176341
177342instance
178343 ( FiniteSumElem self b
179344 , Finite self a ~ 'False
180345 , Finite self b ~ 'True
181346 ) => FiniteSum self a b 'False 'True where
182− finiteSum = fmap R1 <$> finiteElem @self @b
347+ finiteSum _ = fmap R1 <$> finiteElem (Proxy :: Proxy self)
183348
184349class FiniteSumElem self a where
185− finiteElem :: [Gen (a p)]
350+ finiteElem :: Proxy self -> [Gen (a p)]
186351
187352instance
188353 ( FiniteSum self a b af bf
189354 ) => FiniteSumElem self (a :+: b) where
190− finiteElem = finiteSum @self
355+ finiteElem _ = finiteSum (Proxy :: Proxy self)
191356
192357instance
193− ( GArbitrary self (C1 c f) 'True
194− ) => FiniteSumElem self (C1 c f) where
195− finiteElem = [gArbitrary @self]
358+ ( GArbitrary self (M1 C c f) 'True
359+ ) => FiniteSumElem self (M1 C c f) where
360+ finiteElem _ = [gArbitrary (Proxy :: Proxy self)]
361+
196362
363+#if __GLASGOW_HASKELL__ >= 800
197364instance
198365 ( TypeError (ShowType self :<>: Text " refers to itself in all constructors")
199366 , (Finite self a || Finite self b) ~ 'False
200− ) => GArbitrary self (D1 t (a :+: b)) 'False where
201− gArbitrary = error "Unreachable"
367+ ) => GArbitrary self (M1 D t (a :+: b)) 'False where
368+ gArbitrary _ = error "Unreachable"
369+#endif
202370
203371genericArbitrary
204372 :: forall a ga some
205373 . (Generic a, GArbitrary a ga some, ga ~ Rep a)
206374 => Gen a
207−genericArbitrary = G.to <$> gArbitrary @a
375+genericArbitrary = G.to <$> gArbitrary (Proxy :: Proxy a)