Test separate compilation with indexed types

testsuite/tests/ghc-regress/indexed-types/Ind2_help.hs

+{-# OPTIONS -findexed-types #-}
+
+module Ind2_help where
+
+class C a where
+  data T a :: *
+  unT :: T a -> a
+  mkT :: a -> T a
+
+instance (C a, C b) => C (a,b) where
+  data T (a,b) = TProd (T a) (T b)
+  unT (TProd x y) = (unT x, unT y)
+  mkT (x,y)       = TProd (mkT x) (mkT y)
+

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

-test('ind1', normal, compile, [''])
+test('ind1', normal, compile, [''])
+test('ind2', normal, multimod_compile, ['ind2', '-v0'])
+clean(['Ind2_help.hi', 'Ind2_help.o'])

testsuite/tests/ghc-regress/indexed-types/ind2.hs

+{-# OPTIONS -findexed-types #-}
+
+module ShouldCompile where
+
+import Ind2_help(C(..))
+
+zipT :: (C a, C b) => T a -> T b -> T (a,b)
+zipT x y = mkT (unT x, unT y)
+