Add test case T8018

testsuite/tests/indexed-types/should_compile/T8018.hs

+{-# LANGUAGE TypeFamilies #-}
+
+module T8018 where
+
+data Foo a = Bar (F a)
+
+type family F a where
+  F (Foo a) = Bool
\ No newline at end of file

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

@@ -225,3 +225,5 @@ test('T8011',
      normal,
      run_command,
      ['$MAKE -s --no-print-directory T8011'])
+
+test('T8018', normal, compile, [''])
\ No newline at end of file