Test for empty type indices (Trac #2888)

testsuite/tests/ghc-regress/indexed-types/should_fail/T2888.hs

+{-# LANGUAGE TypeFamilies #-}
+-- Test for no type indices
+
+module T2888 where
+
+class C w where 
+  data D:: * -> *

testsuite/tests/ghc-regress/indexed-types/should_fail/T2888.stderr

+
+T2888.hs:7:2:
+    Type family constructor `D' must have at least one type index parameter
+    In the class declaration for `C'

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

@@ -47,3 +47,4 @@ test('T2157', normal, compile_fail, [''])
 test('T2203a', normal, compile_fail, [''])
 test('T2627b', normal, compile_fail, [''])
 test('T2693', normal, compile_fail, [''])
+test('T2888', normal, compile_fail, [''])