Allow optional instance keyword in associated type family instances

Add the missing branch for parsing the optional 'instance' keyword
in associated type family instance declarations.

Fixes #13747

Reviewers: austin, bgamari

Reviewed By: bgamari

Subscribers: simonpj, RyanGlScott, rwbarton, thomie, mpickering

Differential Revision: https://phabricator.haskell.org/D3673

2 files changed, 25 insertions, 0 deletions

diff --git a/testsuite/tests/parser/should_compile/T13747.hs b/testsuite/tests/parser/should_compile/T13747.hs
new file mode 100644
index 0000000000..749d8d2fc4
--- /dev/null
+++ b/testsuite/tests/parser/should_compile/T13747.hs
@@ -0,0 +1,24 @@
+{-# LANGUAGE TypeFamilies #-}
+{-# LANGUAGE GADTs #-}
+
+module T13747 where
+
+class C a where
+  type family TC a :: *
+
+class D a where
+  data family TD a :: *
+
+instance C Int where
+  type instance TC Int = Int
+
+instance D Double where
+  data instance TD Double = TDDouble
+
+instance D Int where
+  newtype instance TD Int = TDInt Int
+
+instance D Char where
+    data instance TD Char where
+        C1 :: TD Char
+        C2 :: TD Char
diff --git a/testsuite/tests/parser/should_compile/all.T b/testsuite/tests/parser/should_compile/all.T
index 2059979765..a9d6830701 100644
--- a/testsuite/tests/parser/should_compile/all.T
+++ b/testsuite/tests/parser/should_compile/all.T
@@ -107,3 +107,4 @@ test('T10582', expect_broken(10582), compile, [''])
 test('DumpParsedAst',      normal, compile, ['-dsuppress-uniques -ddump-parsed-ast'])
 test('DumpRenamedAst',     normal, compile, ['-dsuppress-uniques -ddump-rn-ast'])
 test('DumpTypecheckedAst', normal, compile, ['-dsuppress-uniques -ddump-tc-ast'])
+test('T13747', normal, compile, [''])