T2693

testsuite/tests/ghc-regress/indexed-types/should_fail/T2693.hs

+{-# LANGUAGE TypeFamilies #-}
+
+module T2693 where
+
+type family TFn a :: *
+
+f :: Maybe ()
+f = do
+  let Just x = undefined :: Maybe (TFn a)
+  let n = fst x + fst x
+  return ()

testsuite/tests/ghc-regress/indexed-types/should_fail/T2693.stderr

+
+T2693.hs:10:14:
+    Couldn't match expected type `(a1, b)'
+           against inferred type `TFn a'
+    In the first argument of `fst', namely `x'
+    In the first argument of `(+)', namely `fst x'
+    In the expression: fst x + fst x

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

@@ -46,3 +46,4 @@ test('T1900', normal, compile_fail, [''])
 test('T2157', normal, compile_fail, [''])
 test('T2203a', normal, compile_fail, [''])
 test('T2627b', normal, compile_fail, [''])
+test('T2693', normal, compile_fail, [''])