Fill in associated type defaults with DeriveAnyClass

Summary:
Unlike `-XDefaultSignatures`, `-XDeriveAnyClass` would not fill in
associated type family defaults when deriving a class which contained
them.

In order to fix this properly, `tcATDefault` needed to be used from
`TcGenDeriv`. To avoid a module import cycle, `tcATDefault` was moved
from `TcInstDcls` to `TcClsDcl`.

Fixes #10361.

Test Plan: ./validate

Reviewers: kosmikus, dreixel, bgamari, austin, simonpj

Subscribers: thomie

Differential Revision: https://phabricator.haskell.org/D1283

GHC Trac Issues: #10361

3 files changed, 92 insertions, 0 deletions

diff --git a/testsuite/tests/generics/T10361a.hs b/testsuite/tests/generics/T10361a.hs
new file mode 100644
index 0000000000..cc5fbb9dca
--- /dev/null
+++ b/testsuite/tests/generics/T10361a.hs
@@ -0,0 +1,32 @@
+{-# LANGUAGE DeriveAnyClass #-}
+{-# LANGUAGE StandaloneDeriving #-}
+{-# LANGUAGE TypeFamilies #-}
+module T10361a where
+
+class C1 a where
+  type T1 a
+  type instance T1 a = Char
+
+class C2 a where -- equivalent to C1
+  type T2 a
+  type instance T2 a = Char
+
+class C3 a where -- equivalent to C1, C2
+  type T3 a
+  type instance T3 a = Char
+
+data A = B
+  deriving C1
+
+deriving instance C2 A
+
+instance C3 A
+
+test1 :: T1 A
+test1 = 'x'
+
+test2 :: T2 A
+test2 = 'x'
+
+test3 :: T3 A
+test3 = 'x'
diff --git a/testsuite/tests/generics/T10361b.hs b/testsuite/tests/generics/T10361b.hs
new file mode 100644
index 0000000000..6ecd99e644
--- /dev/null
+++ b/testsuite/tests/generics/T10361b.hs
@@ -0,0 +1,58 @@
+{-# LANGUAGE DefaultSignatures #-}
+{-# LANGUAGE DeriveAnyClass #-}
+{-# LANGUAGE DeriveGeneric #-}
+{-# LANGUAGE FlexibleContexts #-}
+{-# LANGUAGE TypeFamilies #-}
+{-# LANGUAGE TypeOperators #-}
+{-# LANGUAGE UndecidableInstances #-}
+
+module T10361b where
+
+import GHC.Generics
+
+---------------------------------------------------------------------
+class Convert a where
+    type Result a
+    type instance Result a = GResult (Rep a)
+
+    convert :: a -> Result a
+    default convert :: (Generic a, GConvert (Rep a)) => a -> GResult (Rep a)
+    convert x = gconvert (from x)
+
+instance Convert Float where
+    type Result Float = Float
+    convert = id
+
+instance Convert Int where
+    type Result Int = Int
+    convert = id
+
+---------------------------------------------------------------------
+class GConvert f where
+    type GResult f
+    gconvert :: f p -> GResult f
+
+instance (Convert c) => GConvert (K1 i c) where
+    type GResult (K1 i c) = Result c
+    gconvert (K1 x) = convert x
+
+instance (GConvert f) => GConvert (M1 i t f) where
+    type GResult (M1 i t f) = GResult f
+    gconvert (M1 x) = gconvert x
+
+instance (GConvert f, GConvert g) => GConvert (f :*: g) where
+    type GResult (f :*: g) = (GResult f, GResult g)
+    gconvert (x :*: y) = (gconvert x, gconvert y)
+
+---------------------------------------------------------------------
+
+data Data1 = Data1 Int Float
+    deriving (Generic)
+
+instance Convert Data1
+
+val :: (Int, Float)
+val = convert $ Data1 0 0.0
+
+data Data2 = Data2 Int Float
+    deriving (Generic, Convert)
diff --git a/testsuite/tests/generics/all.T b/testsuite/tests/generics/all.T
index 31a6809c82..cbf70cf8bf 100644
--- a/testsuite/tests/generics/all.T
+++ b/testsuite/tests/generics/all.T
@@ -40,3 +40,5 @@ test('T8468', normal, compile_fail, [''])
 test('T8479', normal, compile, [''])
 test('T9563', normal, compile, [''])
 test('T10030', normal, compile_and_run, [''])
+test('T10361a', normal, compile, [''])
+test('T10361b', normal, compile, [''])