New tests for #8368.

testsuite/tests/indexed-types/should_fail/T8368.hs

+{-# LANGUAGE TypeFamilies, GADTs #-}
+
+module T8368 where
+
+data Foo = Bar
+
+data family Fam a
+data instance Fam a where
+  MkFam :: Foo
+  
\ No newline at end of file

testsuite/tests/indexed-types/should_fail/T8368.stderr

+
+T8368.hs:9:3:
+    Data constructor ‛MkFam’ returns type ‛Foo’
+      instead of an instance of its parent type ‛Fam’
+    In the definition of data constructor ‛MkFam’
+    In the data instance declaration for ‛Fam’

testsuite/tests/indexed-types/should_fail/T8368a.hs

+{-# LANGUAGE TypeFamilies, GADTs #-}
+
+module T8368a where
+
+data family Fam a b
+data instance Fam Int b where
+  MkFam :: Fam Bool b
+  
\ No newline at end of file

testsuite/tests/indexed-types/should_fail/T8368a.stderr

+
+T8368a.hs:7:3:
+    Data constructor ‛MkFam’ returns type ‛Fam Bool b’
+      instead of an instance of its parent type ‛Fam Int b’
+    In the definition of data constructor ‛MkFam’
+    In the data instance declaration for ‛Fam’

testsuite/tests/indexed-types/should_fail/all.T

@@ -116,3 +116,5 @@ test('T8129',
      run_command,
      ['$MAKE -s --no-print-directory T8129'])
 
+test('T8368', normal, compile_fail, [''])
+test('T8368a', normal, compile_fail, [''])
\ No newline at end of file